SS 2 First Term

Learning Objectives

• Describe the parts of a computer system and the IPO model.
• Explain the role of the processor in a computer.
• Describe the system bus and the fetch-execute cycle.
• Trace the movement of data and instructions in a cycle.

Review of Computer System and IPO Model

A computer system is made up of four essential parts that must work together for the machine to be useful. Hardware refers to all the physical parts, including the CPU, RAM, hard drive, keyboard and monitor. Software refers to the programmes and instructions that tell the hardware what to do, such as the operating system and applications like Microsoft Word. Data consists of raw facts, such as numbers, text, images and sound, that the computer processes into useful information. Users and procedures are the people who operate the computer and the rules they follow. Without any one of these four parts, the computer cannot function properly. Hardware without software is just an inert machine, while software without hardware has nothing to run on.

The IPO model explains how a computer processes data. Input is when data enters the system, for example when barcodes are scanned at a supermarket checkout or when a student types on a keyboard. Process is when the CPU works on that data, such as adding prices together or sorting a list of names. Output is when the result is produced, for example when a receipt is printed or a result appears on screen. Storage is when data or results are saved for later use, such as when the day's sales figures are written to a hard drive. The centre of the process stage is always the CPU, which is the main topic of this week's study.

Hardware is organised by function. Input devices include the keyboard, mouse, scanner and microphone. The processing device is the CPU itself. Output devices include the monitor, printer and speakers. Storage devices include the hard drive, solid-state drive and flash drive. Software is divided into system software, such as the operating system, and application software, such as a word processor or web browser. This review of SS1 topics provides the foundation for understanding how the CPU actually works inside the machine.

Computer Architecture and the CPU

Computer architecture is the design and structure of a computer's internal components and how they are organised to work together. It describes the CPU, memory, buses and the way instructions move between them. The most widely taught model is the Von Neumann architecture, in which the CPU fetches instructions and data from the same memory, processes them, and stores results back. This is the classic model that most modern computers follow.

The CPU consists of three main components. The Arithmetic Logic Unit (ALU) performs arithmetic operations such as addition, subtraction, multiplication and division, and logical operations such as AND, OR, NOT and comparisons like greater than, less than and equal to. When a spreadsheet computes a class average, the ALU performs the addition and division step by step. The Control Unit (CU) does not perform calculations itself. Instead, it directs the flow of work by fetching instructions from memory, decoding them to understand what they mean, and coordinating the ALU, memory and input/output devices to carry them out. It also controls the system clock that synchronises all operations.

Registers are extremely fast storage locations inside the CPU, much faster than main memory but very small in size. The Program Counter (PC) holds the address of the next instruction to be executed. The Memory Address Register (MAR) holds the address of the memory location being read from or written to. The Memory Data Register (MDR) holds the actual data or instruction being transferred. The Accumulator (ACC) stores the result of the most recent arithmetic or logical operation. The Instruction Register (IR) holds the current instruction being executed.

The System Bus and the Fetch-Execute Cycle

A bus is a set of parallel wires that carries information between the CPU, memory and other devices. The data bus carries the actual data being transferred between components. The address bus carries the memory addresses that tell the CPU where data is going or coming from. The control bus carries control signals such as read and write commands that coordinate the operations. The three buses work together so that the CPU can locate data, move it and control the timing of each transfer.

The CPU carries out every instruction using a repeated cycle known as the fetch-execute or machine cycle. In the fetch step, the CPU reads the next instruction from memory, using the PC to supply the address and the MAR and MDR to transfer it. In the decode step, the Control Unit interprets what the instruction means. In the execute step, the ALU or other component carries out the instruction. In the store step, the result is written back to memory or a register. The PC is then updated to point to the next instruction and the entire cycle repeats. This cycle runs millions or billions of times per second, and the clock speed measured in gigahertz (GHz) tells how many cycles the CPU can perform each second.

For example, when the program must add two numbers 5 and 3, the CPU first fetches the instruction to add 5 and 3 from memory. The Control Unit decodes it as an addition operation. The ALU performs the addition and produces 8. The result is stored in the accumulator or written back to memory. All the CPU components work together in this process. The CU fetches and decodes, the ALU calculates, registers hold temporary values, and buses carry addresses, data and control signals. This co-ordinated behaviour of components is what computer architecture means in practice.

Fetch-execute cycle means the repeated steps of fetching, decoding and executing an instruction.

System bus means the set of wires that carries data, addresses and control signals.

Practical Work

1. Draw the input, process and output model and label each stage.
2. List the three buses and state what each carries.
3. Describe the steps of the fetch-execute cycle in order.
4. Name the parts of the processor and one job of each.

Scenario-Based Questions

1. During a practical class, a student is asked to trace what happens inside the CPU when it processes an instruction that adds the numbers 5 and 3. Walk through the fetch, decode, execute and store steps of the fetch-execute cycle, and state which CPU component (ALU, Control Unit, registers or buses) performs each job.
2. A school technician explains that the CPU in Lab A runs at 3.5 GHz while Lab B runs at 2.8 GHz. What does clock speed measure, and would Lab A always finish every task faster? Give a reason.
3. Two students argue about whether the ALU or the Control Unit is more important in the CPU. Compare the roles of the ALU and the Control Unit and explain why both are needed.
4. A technician notes that the data bus and the address bus carry different kinds of information. Explain what the data bus carries, what the address bus carries and how the control bus co-ordinates the transfer between the CPU and memory.
5. During a practical test a student is asked to trace an ADD instruction, using the two numbers 5 and 3, from memory to execution. Describe each step of the fetch-execute cycle and state what the registers PC, MAR, MDR and IR are used for at each stage.
6. A computer science teacher says most personal computers follow the Von Neumann architecture, in which the CPU fetches instructions and data from the same memory. Explain what this design says about where instructions and data are stored and why it is the most widely taught model.
7. A new desktop has a clock speed of 4.0 GHz. Explain what 4.0 GHz means in terms of the fetch-execute cycle and state how many fetch-execute cycles the CPU can carry out in one second.

Learning Objectives

• Distinguish between RAM and ROM.
• Describe cache memory and the memory hierarchy.
• Explain how the processor uses main memory.
• Explain why a computer uses virtual memory.

RAM and ROM

Main memory is the primary working memory inside a computer that the CPU accesses directly. It stores the instructions and data that the CPU is currently working with. Without main memory, the CPU would have no instructions to execute and no data to process. The two main categories of main memory are RAM and ROM, and each serves a different purpose.

RAM (Random Access Memory) is volatile memory, meaning it loses all its contents when the computer is switched off. It temporarily holds the programmes and data that are currently in use. When you open a web browser, a Word document or a game, its contents are loaded from secondary storage into RAM so that the CPU can access them quickly. There are two main types of RAM. DRAM (Dynamic RAM) is the most common type used in personal computers. It stores each bit of data in a tiny capacitor that leaks charge over time, so it must be refreshed thousands of times per second to maintain its data. DRAM is relatively cheap and dense, which is why it is used for the main system memory in laptops and desktops. A typical school computer in Abuja may have 4 GB or 8 GB of DRAM. SRAM (Static RAM) uses flip-flop circuits to store each bit and does not need refreshing. It is much faster than DRAM but also more expensive and takes up more space on the chip. Because of its speed, SRAM is used for cache memory rather than as the main system RAM.

ROM (Read-Only Memory) is non-volatile memory, meaning it retains its contents even when the power is switched off. It stores the permanent instructions the computer needs to start up, such as the BIOS (Basic Input/Output System) or UEFI firmware. ROM is called read-only because under normal operation the CPU can read from it but cannot easily write new data to it. When you press the power button on a school computer, the ROM provides the first set of instructions that tell the CPU how to initialise the hardware, check memory and load the operating system from the hard drive. Some modern forms of ROM, such as EEPROM and flash memory, allow limited writing, which is how firmware updates work.

Virtual memory means space on storage used as extra memory when RAM is full.

Cache Memory and the Memory Hierarchy

Cache memory is very fast, small memory located on or very close to the CPU chip. It stores copies of frequently accessed data and instructions from RAM so that the CPU can retrieve them much faster than going to main memory every time. There are typically three levels of cache. L1 cache is inside each CPU core, very small (32 KB to 256 KB) and the fastest. L2 cache is inside or near each core, larger (256 KB to 1 MB) and very fast. L3 cache is shared among all cores, the largest (2 MB to 64 MB), fast but slower than L1 and L2.

When the CPU needs data, it checks L1 first. If the data is there, this is called a cache hit and the data is retrieved instantly. If it is not there, this is called a cache miss, and the CPU then checks L2, then L3, and finally goes to RAM. The closer the data is to the CPU, the faster it can be used. Memory in a computer is arranged in a hierarchy from the fastest, smallest and most expensive at the top to the slowest, largest and cheapest at the bottom. CPU registers are at the top, followed by L1, L2 and L3 cache, then main memory (RAM) with 4 GB to 32 GB, and secondary storage (hard drives and SSDs) at the bottom with 256 GB to several terabytes. The hierarchy exists because fast memory is expensive. By keeping the most used data close to the CPU in cache and the rest in RAM or on disk, the computer achieves a good balance of speed and capacity.

Addressable memory refers to the total amount of memory that the CPU can uniquely address using memory addresses. The number of bits in the address bus determines how many unique addresses the CPU can create. A 32-bit address bus can address up to 2 to the power of 32 bytes, which is about 4 GB of RAM. A 64-bit address bus can address far more, theoretically up to 16 exabytes. If a school computer has 8 GB of RAM installed but the operating system only supports 32-bit addressing, it may only be able to use 4 GB of that RAM.

Memory hierarchy means the order of memory from the fastest and smallest to the slowest and largest.

How the CPU Uses Main Memory

During the fetch-execute cycle, the CPU uses main memory at several points. During the fetch step, the Program Counter sends the address of the next instruction to the MAR, which places it on the address bus. The instruction is then read from RAM into the MDR and placed in the Instruction Register. During the decode and execute steps, if the instruction requires data, the data address is sent to the MAR and the data is fetched from RAM into the MDR. During the store step, results are written back to RAM by placing the address in the MAR and the data in the MDR, with a write signal sent on the control bus. Cache speeds up this entire cycle by keeping frequently used instructions and data close to the CPU, reducing the need to wait for slower RAM accesses.

Practical Work

1. Draw a table comparing RAM and ROM.
2. Arrange cache, RAM, and storage in order of speed.
3. Explain why cache is placed close to the processor.
4. Describe what happens when RAM is full.

Scenario-Based Questions

1. A student opens a web browser, a Word document and a game at the same time on a computer with 4 GB of RAM. Explain why these programs must be loaded from secondary storage into RAM before the CPU can use them, and what happens to their contents when the computer is switched off.
2. A technician is choosing between DRAM and SRAM for different roles inside a computer. Compare DRAM and SRAM in terms of speed, cost and typical location inside the computer.
3. A school purchases new desktops with 8 GB of RAM. The technician says a 32-bit operating system would not use all of it. Explain why a 32-bit OS can address at most 4 GB and how a 64-bit OS solves this.
4. When a computer starts up, it first loads instructions from ROM. Explain what BIOS or UEFI does during boot and why ROM is used instead of RAM for this purpose.
5. A developer is designing a system and must choose between L1, L2 and L3 cache. Explain the memory hierarchy from L1 to main memory and why faster cache is always smaller.
6. During the fetch-execute cycle, the CPU copies an instruction address from the PC into the MAR. Explain why the MAR and MDR are needed rather than sending data directly between the PC and the CPU.
7. A student says RAM is faster than ROM so ROM should be replaced with RAM. Explain why this would prevent the computer from starting up and why both types of memory are necessary.

Learning Objectives

• Describe magnetic and optical storage devices.
• Describe solid state storage and compare storage devices.
• Explain cloud storage and the choice between capacity and performance.
• Describe the working mechanisms of secondary storage.

Magnetic and Optical Storage

Secondary storage is non-volatile, long-term storage that retains data and programmes even when the computer is switched off. Unlike RAM, which is fast but small and temporary, secondary storage is much larger but slower. It holds the operating system, application programmes, documents, photos, videos and all other user files. Secondary storage devices come in three main technologies, magnetic, optical and solid-state.

A Hard Disk Drive (HDD) stores data on spinning circular platters coated with a magnetic material. A read/write head on a mechanical arm moves across the surface of each platter to read or write binary data by changing the magnetic orientation of tiny areas. The platters spin at high speed, typically 5,400 or 7,200 revolutions per minute (RPM) in a laptop and up to 10,000 or 15,000 RPM in a server. The faster the platters spin, the faster data can be accessed. HDDs offer large capacities at a relatively low cost. A typical desktop HDD in Nigeria today may have 500 GB to 1 TB of storage, enough for thousands of documents, photos and music files. However, HDDs have moving parts, making them vulnerable to shock and drops, and they consume more power than solid-state alternatives.

Optical storage uses a laser to read and sometimes write data encoded as tiny pits and lands on the surface of a reflective disc. The three main types are the CD (Compact Disc) with 700 MB capacity, used for music and small software installers, the DVD (Digital Versatile Disc) with 4.7 GB to 8.5 GB, used for movies and large software packages, and the Blu-ray Disc with 25 GB to 50 GB, used for high-definition video and large data archives. Optical storage is less common in modern computing because flash drives and cloud storage have largely replaced it for everyday use, though DVDs are still used for distributing software in some Nigerian schools and offices.

Solid state drive means a fast storage device with no moving parts.

Solid-State Storage and Device Comparison

A Solid-State Drive (SSD) stores data using flash memory chips, which are electronic circuits that retain data without any moving parts. Because there are no mechanical components, SSDs are much faster than HDDs, more resistant to shock and drops, and produce no noise or vibration. SSDs are now standard in most new laptops and desktops. A typical SSD in a Nigerian school or office computer may have 256 GB to 1 TB of storage. While the cost per gigabyte is higher than an HDD, the performance improvement is significant, especially for starting up the computer, opening programmes and loading files.

USB flash drives, also called thumb drives or pen drives, are small, portable solid-state storage devices that connect to a computer via a USB port. They are widely used in Nigerian schools for transferring files between computers, submitting assignments and carrying data from home to school. Memory cards, such as SD cards and microSD cards, are even smaller solid-state devices used in cameras, phones, tablets and other portable devices. A typical phone in Nigeria may use a 64 GB or 128 GB microSD card to expand its internal storage for photos, music and videos. Both USB flash drives and memory cards use flash memory technology, differing mainly in their connector type and physical form factor.

Cloud Storage and Capacity or Performance

Cloud storage is a service that stores data on remote servers managed by a provider, and users access their files over the internet. Instead of saving a file only on a local hard drive, the file is also uploaded to servers in a data centre. Popular services include Google Drive, Microsoft OneDrive, Dropbox and iCloud, many of which offer free tiers such as 15 GB on Google Drive. Cloud storage has several advantages. Files can be accessed from any device with internet access, files are backed up automatically, and files can be shared with others easily. However, cloud storage requires a reliable internet connection, which may be a challenge in some parts of Nigeria, and there are concerns about privacy and data security.

When choosing a storage device, two key factors are capacity and performance. Capacity is how much data the device can hold, measured in gigabytes or terabytes. Performance is how fast the device can read and write data, measured in megabytes per second or gigabytes per second. A school computer storing only text documents may only need 256 GB of storage. A video editing studio may need 2 TB or more. A user who frequently opens large files benefits more from an SSD's fast access speed than from an HDD's low cost per gigabyte. Understanding both capacity and performance helps schools make informed decisions about storage investments.

Secondary Storage Working Mechanisms

Magnetic and optical storage record binary data in completely different physical ways. Magnetic storage, used by the HDD and the older floppy disk, stores data as tiny magnetised regions on a spinning platter. The read and write head releases a small current to line up the magnetic particles in one direction for a 1 and the opposite direction for a 0, and it reads data by detecting the magnetic orientation of the particles as the platter spins beneath it.

Optical storage, used by CDs, DVDs and Blu-ray discs, records data as microscopic pits and lands pressed or burned into a reflective layer. A laser beam is focused on the disc surface, and the reflected light changes when it meets a pit, producing a binary pattern that the drive decodes. Writing requires a stronger laser that physically alters the disc, while reading uses a weaker laser that only senses the surface.

The two mechanisms explain the strengths of each family. Magnetic hard disks are rewritable millions of times and offer high capacity at low cost, but they are sensitive to shock because the head moves physically close to the spinning platter. Optical discs are cheap to press in bulk and resist magnetic interference, but they are slower, hold less data and can be scratched or damaged.

Magnetic storage: magnetised particles represent 0 and 1, read by a moving head.

Optical storage: pits and lands reflect laser light in binary patterns.

HDDs rewrite data repeatedly but are sensitive to physical shock.

Optical media are slower and hold less data but resist magnetic interference.

Storage Media Characteristics

Every storage medium can be judged by four main characteristics: capacity, speed, portability and durability. Capacity is the total amount of data the device can hold, measured in gigabytes or terabytes. Speed is how quickly the device can read and write data, usually described by access time (how long before data can be retrieved) and transfer rate (how much data moves per second).

Portability describes how easily the device can be carried and connected to different computers. A USB flash drive is highly portable because it fits in a pocket and plugs into any USB port, while an internal HDD is not portable because it must be installed inside a machine. Durability covers how well the device survives physical punishment and time. SSDs and flash drives tolerate drops and knocks because they have no moving parts, while HDDs can fail if dropped while spinning and optical discs can scratch.

Real purchase decisions balance these characteristics. A student carrying projects between home and school values portability, so a flash drive or a small external SSD is a good fit. A school archive keeping years of video files values capacity and cost, so a large HDD or networked storage wins. A server that must respond instantly values speed, so it uses NVMe SSDs even though they cost more per gigabyte.

Capacity: the total data a device can hold, in GB or TB.

Speed: access time and transfer rate.

Portability: how easily the device moves between systems.

Durability: resistance to shock, wear and the passage of time.

SSDs are fast and rugged, HDDs give the most capacity for the least money, and optical discs are cheap to press but easy to scratch.

File Organisation and Access Methods

How data is organised on a storage device determines how quickly it can be found. In sequential access, records are read one after another from the start, like a film reel, so finding the tenth record means passing the first nine. This suits backups and log files where every record is processed in order. In direct (also called random) access, the device can jump straight to any location, which is why disks and flash storage are used for files that are opened in any order, such as documents and programs.

Indexed access keeps a separate index table that records where every record is stored. When a file is needed, the system checks the index first and jumps to the exact location, giving fast lookups while still allowing flexible additions. Modern file systems on HDDs and SSDs combine these ideas: a file allocation table acts as an index, and the disk access itself is direct.

The access method is chosen together with the storage medium and the task. Magnetic tapes and some optical formats favour sequential access for streaming large amounts of data cheaply. Hard disks, SSDs and flash drives excel at direct access, and databases rely on indexes to search millions of records almost instantly, which is exactly how a bank in Nigeria finds a customer account among millions in a fraction of a second.

Sequential access: records are read in order (tapes, backups, logs).

Direct access: the device jumps to any location (HDD, SSD, flash).

Indexed access: an index table points straight to each record (databases).

The choice balances speed, storage cost and the needs of the task.

Practical Work

1. Draw a table comparing a hard disk, a solid state drive and a CD.
2. List three examples of cloud storage and one use of each.
3. Explain why a solid state drive is faster than a hard disk.
4. Describe how data is written to and read from an optical disc.

Scenario-Based Questions

1. A school IT manager must choose between an HDD and an SSD for a computer lab where students boot up simultaneously every morning. Compare the two in terms of speed, durability, cost and capacity, then recommend one.
2. A photographer needs to archive 500 GB of high-resolution images that must last at least 20 years. Evaluate HDD, SSD, optical disc (Blu-ray) and cloud storage as options, giving one strength and one weakness of each.
3. A student copies an assignment from the school server to a USB flash drive. Explain what type of storage a USB flash drive uses and why it is faster and more durable than a portable HDD.
4. A company is considering storing employee records on cloud storage instead of a local server. Compare local storage and cloud storage in terms of accessibility, security concerns and ongoing cost.
5. A music CD holds 700 MB while a DVD holds 4.7 GB. Calculate how many CDs would be needed to hold the same amount of data as one DVD, and explain what type of storage a DVD is (magnetic, optical or solid state) and why optical discs are now less common in everyday computing.
6. A user reports that a five-year-old laptop with an HDD takes two minutes to start up but an SSD in the same laptop reduces it to 20 seconds. Explain why the storage device type affects boot time.
7. A bank must decide where to keep copies of its daily transaction records so that a flood at its building cannot destroy them all at once. Compare storing the copies on a local hard drive with storing them on cloud servers, and recommend the better choice for a bank that cannot afford to lose its records.

Learning Objectives

• State the functions and types of an operating system.
• Explain what a software licence is and why it matters.
• Compare proprietary, open source, freeware and shareware.
• Describe commercial and subscription licence types.

Introduction

An operating system (OS) is the most important system software on a computer, sitting between the user, applications and hardware. Without one, the computer cannot run programs. The OS is a resource manager that shares the CPU, memory and devices fairly; a user interface (a GUI desktop or a command line); and a hardware abstraction layer that hides the technical details of printers and disks from programs.

Types of Operating Systems

Operating systems are designed for different jobs. A batch OS processes groups of jobs with no user interaction, as in overnight results. A time-sharing OS switches the CPU between users and programs so each seems to have the machine alone. A real-time OS must respond within strict time limits, as in car brakes and medical monitors. A distributed OS joins separate computers into one apparent system, as in cloud clusters. An embedded OS runs a single device such as a smart TV. A mobile OS powers smartphones with touch interfaces and app stores. A network OS on a server manages users and resources centrally. A multiprocessor OS divides work across several CPUs or cores.

Multi-user means an operating system that serves several users at once.

Real time means an operating system that responds within a fixed, short time.

Common Operating Systems

Windows, by Microsoft, is the most widely used desktop OS. The family grew from Windows XP through 7, 10 and 11. It uses the NTFS file system, keeps settings in the Windows Registry, and supports the widest range of hardware and software.

macOS is Apple's UNIX-based desktop OS. The Finder manages files, and Gatekeeper blocks unverified software. Its tight integration with iPhone and iPad suits creative professionals.

Linux is an open-source, UNIX-like OS. Linus Torvalds wrote its kernel in 1991 and released it under the GPL, so modified versions must stay open source. Free, stable and secure, it dominates web servers and comes in many distributions.

Ubuntu, by Canonical, is the most popular Linux distribution. Its Long Term Support (LTS) releases get five years of updates, its desktop eases the move from Windows, and its apt package manager installs software from online repositories, all free for budget-limited schools.

Kali Linux, by Offensive Security, is built for penetration testing and cybersecurity. It ships with over 600 security tools and is not for daily school work.

Android, by Google, is a mobile OS on the Linux kernel, open at its core (AOSP) so brands like Tecno, Infinix and Samsung adapt it. Google Play Services adds the Play Store and Google apps. It dominates Nigerian phones at every price.

iOS is Apple's closed-source mobile OS for iPhone and iPad. UNIX-based and sold only through the App Store, it offers smooth performance and strong security, but costs more.

Unix, built at Bell Labs in 1969 by Ken Thompson and Dennis Ritchie, is the ancestor of Linux, macOS and Solaris. The POSIX standard keeps Unix-like systems compatible, and Unix still powers mainframes and enterprise servers.

Solaris, from Sun Microsystems and now Oracle, is a UNIX-based server OS on SPARC and x86. Its ZFS file system protects data integrity and DTrace diagnoses live systems for critical servers.

Chrome OS, by Google, is built on Linux around the Chrome browser. It is cloud-first, keeping files in Google Drive, and supports Android apps. Cheap Chromebooks are common in education.

DOS (Disk Operating System), especially MS-DOS for IBM in 1981, was the command-line predecessor of Windows. Users typed commands like DIR and COPY before Windows took over.

Functions of an Operating System

Memory management allocates RAM to programs and reclaims it when they close, using disk-based virtual memory when RAM fills. Process management controls which programs run and how they share the CPU, switching so fast that multitasking seems simultaneous. File management organises files and records names, locations and permissions using file systems such as NTFS (Windows), ext4 (Linux) and APFS (macOS). Device management controls peripherals through drivers, so plugging in a USB drive works at once. Security enforces logins, permissions and encryption so one student cannot read another's files. Networking manages Wi-Fi and printer sharing on a LAN, and the interface (GUI or CLI) gives people command of the machine.

Advanced Operating System Engineering

Inside every operating system lies a structure that connects hardware and software. The kernel is the core program that always stays in memory and controls the processor, memory and devices. Device drivers are small programs that translate the commands of the operating system into the exact instructions of specific hardware, such as a printer or network card. The shell is the outer layer the user sees, either a command-line shell where the user types commands or a graphical shell with windows and icons.

Kernel: the core program that manages the processor, memory and devices.

Device drivers: programs that translate OS commands for specific hardware.

Shell: the command-line or graphical interface between the user and the kernel.

A protected kernel prevents faulty applications from crashing the whole system.

The layers work together: the user clicks icons in the shell, the shell passes the request to the kernel, the kernel asks the device driver to manage the hardware, and the result appears on screen. This is why a new printer will not work until its driver is installed.

Resource Allocation, CPU Scheduling and Interrupt Handling

When a user types, plays music and downloads files at the same time, the operating system must share the processor, memory and devices among all the tasks. Resource allocation decides how much of each resource every program gets. CPU scheduling decides which program uses the processor next by rapidly switching between programs, giving each a short slice of time so all programs seem to run together. Interrupts are signals from devices asking for attention, and the operating system responds to each by priority.

Resource allocation: sharing the processor, memory and devices fairly.

CPU scheduling: deciding which program runs next and for how long.

Time slicing: switching quickly between programs so they run smoothly together.

Interrupts: device signals responded to in order of importance.

These mechanisms keep the computer responsive when it is busy. In a cybercafe where several people share one machine, scheduling makes each person feel their work is running smoothly, and when a printer finishes a page, its interrupt helps the next page print without delay.

Comparing Modern Operating Systems

Modern computers run on a small family of operating systems, each with its own strengths. Windows offers a wide software library and strong support for business use, while macOS is valued for its clean design and creative tools. Linux is free and open-source, secure and stable, and popular for servers and programming. On phones, Android powers most devices in Nigeria, while iOS runs on Apple iPhones and iPads.

Windows: broad software support, strong for offices, schools and desktop work.

macOS: clean design and strong creative tools on Apple devices.

Linux: free, open-source, secure and popular for servers and programming.

Android: the most common mobile system in Nigeria.

iOS: Apple system on iPhones and iPads, known for privacy and smooth performance.

There is no single best operating system. The best one depends on the task, the device and the user, so knowing each system strengths helps users choose wisely for school, home or work.

Introduction

Software is the set of programs and instructions that tell hardware what to do. It divides into system software and application software. System software, which includes the operating system, device drivers and utilities, manages and supports the computer in the background, and users rarely handle it directly. Application software performs the tasks users care about, such as writing, calculating, browsing or designing, and it runs on top of system software. The main categories are word processing (Word, Google Docs), spreadsheets (Excel, Google Sheets), presentations (PowerPoint, Google Slides), databases (Access, MySQL), graphics (GIMP, Photoshop) and web browsers (Chrome, Firefox).

Software Licensing

A software licence is a legal contract between the publisher and the user stating how software may be used, copied, modified and distributed. Violating it brings fines, lawsuits or loss of updates.

A proprietary (closed-source) licence hides the source code. The user receives only the compiled program, obtains usage rights rather than ownership, and may not legally modify or redistribute it. Windows, Office and Photoshop are examples.

Open-source licences make source code freely available. Copyleft licences such as the GPL require modified versions to stay open source. Permissive licences such as MIT, BSD and Apache allow derivatives, even proprietary ones, as long as the copyright notice is kept; Apache also grants patent rights.

Freeware is free to use but keeps its source hidden, as with VLC and Skype. Shareware (trialware) is free for a limited trial then paid, as with WinRAR and Adobe trials. Public domain software carries no copyright, so anyone may use it without restriction.

Commercial licences are paid: a per-seat licence covers one machine, a per-user licence covers one person on several devices, a site licence covers all computers at one location, and a volume licence discounts bulk purchases. Subscription licences charge monthly or yearly fees for ongoing access, as with Microsoft 365 and Adobe Creative Cloud. Educational licences give free or discounted access to qualifying schools and charities, such as Microsoft 365 Education and Google Workspace for Education.

Proprietary software means software whose source code is hidden.

Software Categories

Beyond the operating system, software falls into three categories. System software keeps the machine working: the OS, device drivers and utilities such as antivirus, backup and disk cleaners. Application software carries out user tasks such as word processing, browsing and design. Programming software supports developers with compilers, interpreters and IDEs such as Visual Studio Code that bundle an editor, debugger and build tools.

Practical Application Scenarios

Installing software runs an installer file (.exe or.dmg) that copies program files, creates shortcuts and registers the application with the OS. During installation the user accepts the End User License Agreement (EULA), the licence text stating the rules of use. Smartphones install apps from the Play Store or App Store, which handle updates automatically.

Choosing between open-source and proprietary depends on budget, features and support. LibreOffice gives schools free word processing, spreadsheet and presentation tools that cover most tasks, while businesses needing specific compatibility may pay for proprietary products. Reading the EULA and keeping a software inventory (every program, its licence type and valid installs) protects against licence violations.

Software as a Service (SaaS) delivers applications online: the user pays a subscription, works in a browser and stores files in the cloud, as with Google Workspace and Microsoft 365. Traditional licensing installs owned software on a device. SaaS lowers upfront cost and aids collaboration but needs reliable internet and never grants ownership.

Impact of Choosing the Wrong Licence

Choosing or managing the wrong licence is illegal and costly. Pirated copies carry legal penalties and often hide malware that infects machines and steals records. A business installing a per-seat licence on twice as many computers as purchased fails an audit and pays penalties. Using an educational licence for profit cancels the licence. Authorised software, open-source alternatives and free education programmes remove this risk and set students a responsible example.

Productivity Suites

A productivity suite is a group of related application programs sold together as one package. The most common tools in a productivity suite are the word processor, the spreadsheet and the presentation program. Nigerian schools, offices and businesses rely on these suites every day for writing documents, calculating data and presenting information.

Word processing software creates, edits, formats and prints text documents such as letters, lesson plans and reports. Microsoft Word, Google Docs and LibreOffice Writer are common examples. Features include bold and italic text, bullet lists, page numbers and spell checking.

Spreadsheet software organises data in rows and columns and performs calculations automatically. Microsoft Excel, Google Sheets and LibreOffice Calc record scores, calculate averages, produce report sheets and track budgets. Formulas let the software compute values instantly, such as adding a whole column or finding the highest score in a class.

Presentation software creates visual slideshows for communicating with an audience. Microsoft PowerPoint, Google Slides and LibreOffice Impress are widely used in Nigerian classrooms for projects and science fairs. Concise text, images and diagrams support the speaker during a talk.

The tools in a suite share a familiar interface and work together. A spreadsheet table can be copied into a word processor document, and spreadsheet data can be embedded in a presentation slide, saving time and keeping documents consistent.

Word Processing Formatting

Formatting options in a word processor help organise text and make documents look professional. The most useful features include tables, headers and footers, and page setup.

Tables organise information into rows and columns so data can be compared side by side. A student can create a table of subjects and scores, and a teacher can build a timetable. In Microsoft Word, column widths, borders and cell shading can all be adjusted.

Headers appear at the top of every page and carry the document title or school name, while footers at the bottom carry page numbers and dates. Headers and footers help readers navigate longer reports.

Page setup controls margins, paper size and orientation. Margins are the blank edges around the page, the standard paper size in Nigeria is A4, and orientation can be portrait (vertical) or landscape (horizontal) depending on the content.

Font size, line spacing, indentation and alignment also shape a document. A readable font such as Arial or Times New Roman at size 12 with 1.5 line spacing satisfies standard academic requirements in Nigerian schools.

Desktop Publishing Software and Design Principles

Desktop publishing, or DTP, uses specialised software to create professionally designed documents. DTP software is built for complex layouts combining text, images, graphics and precise formatting.

Popular DTP programs include Adobe InDesign, Canva, CorelDRAW and the free and open-source Scribus. Nigerian print shops and publishers use DTP software for school magazines, newsletters, posters, certificates, brochures and examination papers.

DTP differs from a word processor because it focuses on layout and visual design rather than plain text writing. Users control the exact position of text boxes, images, lines and colour blocks, and master pages apply consistent headers, footers and page numbers across all pages.

Good DTP design follows key principles. Balance spreads visual elements evenly, contrast draws attention to headlines, proximity groups related items together, and consistency keeps fonts, colours and spacing uniform throughout a document.

A school club newsletter shows these principles in action: two or three fonts chosen for headlines and body text, a colour scheme matching school colours, a master page carrying the school logo, and clear headings with whitespace that make the layout easy to read.

Practical Work

1. List five functions of an operating system.
2. Draw a table of four licence types and one example of each.
3. Explain the difference between open source and freeware.
4. Explain why pirated software is not an acceptable option.

Scenario-Based Questions

1. A school with a small budget needs office software for 30 computers. Recommend a licence and justify it.
2. A learner installs software on more computers than the licence allows. Explain the risk.
3. Explain why a driver must be installed before a new printer will work.
4. Explain how an operating system keeps several programs running at once.

Learning Objectives

• Explain place value in the decimal, binary, octal and hexadecimal systems.
• Convert numbers between decimal, binary and hexadecimal.
• Explain how characters, images and sound are represented.
• Use the units that measure file sizes.

Understanding Number Systems

A number system is a way of writing numbers using a fixed set of symbols called digits and a base (the radix). The base tells how many digits the system uses and what each position is worth. The four common systems are binary (base 2), octal (base 8), decimal (base 10) and hexadecimal (base 16). Number systems matter because computer hardware can only recognise two states, on and off; every value it stores must first be turned into patterns of 0s and 1s, so binary is the native language of computing and the other systems are shorthand ways of writing it.

The table below introduces the four systems.

Binary Number System

Binary uses only the digits 0 and 1, and each position is worth a power of 2, working from the right, namely 1, 2, 4, 8, 16, 32, 64, 128. To convert binary to decimal, add the place values that carry a 1, so binary 1101 = 8 + 4 + 1 = 13, binary 10110 = 16 + 4 + 2 = 22, and binary 1100100 = 64 + 32 + 4 = 100.

Converting Decimal to Binary

To convert decimal to binary, divide the number repeatedly by 2, write down the remainder each time and stop when the quotient becomes 0, then read the remainders from bottom to top. For decimal 25, 25/2 = 12 r 1, 12/2 = 6 r 0, 6/2 = 3 r 0, 3/2 = 1 r 1, 1/2 = 0 r 1, giving binary 11001. For 100 the remainders give 1100100. Check your answer by adding the place values back, for example 16 + 8 + 1 = 25.

Octal Number System

Octal uses the digits 0 to 7, and each position is worth a power of 8, namely 1, 8, 64, 512. To convert octal to decimal, multiply each digit by its place value, for example octal 52 = (5 x 8) + 2 = 42. Because 8 equals 2 to the power of 3, each octal digit represents exactly three binary bits, so binary converts to octal by grouping the bits in threes from the right, so binary 110101 gives 110 and 101, which are 6 and 5, so it is octal 65. To convert decimal to octal, divide by 8 and read the remainders bottom to top, so decimal 63 becomes octal 77.

Hexadecimal Number System

Hexadecimal uses the digits 0 to 9 and the letters A to F, where A = 10, B = 11, C = 12, D = 13, E = 14 and F = 15. Each position is worth a power of 16, namely 1, 16, 256, 4096. To convert to decimal, multiply each symbol by its place value, for example 2A = (2 x 16) + 10 = 42, and FF = (15 x 16) + 15 = 255. Because 16 equals 2 to the power of 4, binary converts to hex by grouping bits in fours from the right, so binary 110101 gives 0011 and 0101, which is hex 35. To convert decimal to hex, divide by 16, so decimal 200 becomes C8, because 200/16 = 12 r 8 and the digit 12 is C.

Hexadecimal is used everywhere because it is compact; one byte, eight bits, is exactly two hex digits, so memory addresses and error codes are far shorter than in binary. Web colour codes such as #FF5733 and debugger memory dumps are also hexadecimal.

ASCII and Character Codes

A computer does not store letters directly; it stores numbers. ASCII, the American Standard Code for Information Interchange, assigns a number to each character. Standard ASCII uses 7 bits and can represent 128 characters, including English letters, digits, punctuation and control codes. Extended ASCII uses 8 bits, one byte, reaching 256 characters. The letter A is decimal 65 (binary 01000001), lowercase a is 97, and the digit 0 is 48. The gap between an uppercase letter and its lowercase form is always 32, which makes case conversion easy.

Unicode

ASCII can only cover English and a few symbols, so Unicode gives a unique number to every character in every writing system, over 140,000 characters today, including Yoruba, Hausa, Igbo, Arabic, Chinese and emoji. Unicode is backwards compatible with ASCII; the first 128 code points are identical. Common forms are UTF-8, which uses 1 to 4 bytes per character, and UTF-16 and UTF-32.

Representing Images

An image is stored as a grid of dots called pixels. Resolution is the number of pixels, written as width x height, so a 1024 x 768 image has 786,432 pixels. Colour depth is the number of bits per pixel; 1 bit gives black and white, 8 bits give 256 colours, and 24 bits give millions. File size = pixels x colour depth, so a 1024 x 768 image at 24 bits is 786,432 x 24 = 18,874,368 bits, about 2,359,296 bytes, roughly 2.4 MB. Higher resolution or colour depth means a sharper but larger image.

Representing Sound

Sound is captured by sampling the wave many times per second. Sampling rate is the number of samples per second (a music CD uses 44,100), bit depth is the bits per sample (16 on a CD), and channels is the number of sound tracks. File size = sampling rate x bit depth x channels x time. One minute of stereo CD audio is 44,100 x 16 x 2 x 60 = 84,672,000 bits, about 10 MB. Higher values give better quality but bigger files.

Representing Video

Video stores a sequence of frames and displays a new one at every frame rate, usually 24 to 30 per second. File size before compression = resolution x colour depth x frame rate x duration. A short video is therefore much larger than a photo because it is hundreds of pictures per second, which is why compression is essential.

Measuring File Sizes

Digital data is measured in bits and bytes. A bit is a single 0 or 1, and a byte is 8 bits, enough for one character. Because computers count in binary, larger units multiply by 1024 (2 to the power of 10), not by 1000, so 1 Kilobyte (KB) = 1024 bytes, 1 Megabyte (MB) = 1024 KB, 1 Gigabyte (GB) = 1024 MB, 1 Terabyte (TB) = 1024 GB and 1 Petabyte (PB) = 1024 TB. Some manufacturers use 1000 when labelling devices, which is why a new drive can show less space than advertised.

Practical Exercises

Test yourself with these problems before the Week 10 assessment.

Convert these binary numbers to decimal, 1010, 11011 and 100000.

Convert these decimal numbers to binary, 18, 37 and 121.

Convert octal 63 and octal 106 to decimal.

Convert decimal 49 and decimal 130 to hexadecimal.

Give the decimal codes for the letters A, a and the digit 0 in ASCII.

State whether each unit equals 1000 or 1024 times the previous unit.

Calculate the size in bytes of an 800 x 600 photo at 24-bit colour.

Estimate the size in megabytes of a 3-minute song with 44,100 samples per second, 16-bit and stereo.

How Computers Represent Data

A computer represents all data using a fixed-length binary pattern. The smallest unit is the bit, which holds a single 0 or 1. Eight bits grouped together form one byte, and a byte is the basic unit used to represent one character such as the letter A. Larger quantities are measured in kilobytes, megabytes, gigabytes and terabytes.

Fixed-length representation means the group of bits set aside for a value keeps a constant size. For example, one byte always holds eight bits, even if the number stored needs only three. This arrangement makes hardware simpler and faster, because the processor always knows where one unit begins and the next ends.

The choice of a fixed pattern also explains why computers use base 2. A transistor has two stable states, on and off, which map naturally to 1 and 0. By grouping many such switches, a computer stores any amount of data, from a single keystroke to a full-length video.

A bit is the smallest unit and holds one 0 or 1.

A byte is eight bits and represents one character.

Storage units grow by multiples of 1024 from the byte upward.

Fixed-length groups keep the processor simple and predictable.

Number Conversions with Worked Examples

Converting between number systems follows two systematic methods. To convert any base to decimal, multiply each digit by its positional value and add the results. To convert from decimal to any base, divide repeatedly by the target base and read the remainders from bottom to top.

Example one: convert binary 11010 to decimal. The place values from the right are powers of 2: 1, 2, 4, 8 and 16. The calculation is (1 times 16) + (1 times 8) + (0 times 4) + (1 times 2) + (0 times 1) = 26 in decimal.

Example two: convert decimal 255 to hexadecimal. Dividing by 16 gives 15 remainder 15, and 15 in hexadecimal is the letter F, so the answer is hex FF. Example three: convert octal 245 to decimal. The place values are 64, 8 and 1, giving (2 times 64) + (4 times 8) + (5 times 1) = 165 in decimal.

Use positional multiplication to convert any base to decimal.

Use repeated division with remainder recording to convert decimal to another base.

Group binary bits in threes for octal and fours for hexadecimal.

Representing Characters, Images, Pixels and Colour Depth

Beyond ASCII and Unicode, computers also encode images as binary data. A digital image is built from a grid of small dots called pixels. Each pixel stores a colour value, and the set of all pixel values together forms the complete picture.

Colour depth is measured in bits per pixel. A 1-bit image shows only black and white. An 8-bit image can display 256 colours. A 24-bit image uses 8 bits for each of the red, green and blue channels, giving over 16 million colours. Web designers meet this idea when they write hex colour codes such as FF0000 for pure red.

Unicode assigns a unique code point to every character across the world writing systems, including Latin, Arabic, Chinese and emoji. Where ASCII supports only 128 characters in 7 bits, Unicode currently maps well over a million code points. A Nigerian user typing in English or Hausa sees the same text reliably on a phone, a computer and a website because all three devices agree on the Unicode standard.

Pixels are the tiny picture elements that make up a digital image.

Colour depth decides how many colours each pixel can show.

24-bit colour supports over 16 million colours for realistic photos.

Unicode covers all world scripts, while ASCII covers English and basic symbols only.

Practical Work

1. Convert the decimal number 45 to binary and to hexadecimal.
2. Write the ASCII code for the letter A in binary.
3. Explain how a colour image is stored using pixels.
4. Arrange bit, byte, kilobyte, megabyte and gigabyte in order.

Scenario-Based Questions

1. A student is asked to convert the binary number 1101 to decimal. Show the conversion step by step and give the answer.
2. A web designer writes a colour as #FF5733 instead of a long run of binary digits. Explain why hexadecimal is more compact than binary for such codes, and calculate the decimal value of the first pair, FF, to show that two hex digits represent one byte (8 bits).
3. A student types the letter A on a keyboard. Explain how the computer stores this character internally using ASCII, giving the decimal code, and explain why ASCII alone cannot represent Yoruba text.
4. A camera captures an image at 1920 x 1080 resolution with 24-bit colour depth. Calculate the uncompressed file size in bytes and convert it to megabytes.
5. A music streaming service records a song at 44,100 samples per second, 16-bit depth and stereo. Explain what each of these three values means and estimate the size of a three-minute recording before compression.
6. A programmer says the hexadecimal value 2A equals decimal 42. Show the conversion to verify this claim, and explain why a computer scientist would prefer to write 2A instead of 00101010.
7. A student confuses kilobytes (KB) with kilobits (Kb). Explain the difference between a bit and a byte, state whether KB equals 1000 or 1024 bytes, and explain why a new hard drive advertised as 1 TB may show less usable space than expected.

Learning Objectives

• Explain what a logic gate is and how it uses bits.
• Draw truth tables for the AND, OR and NOT gates.
• Describe the NAND, NOR, XOR and XNOR gates.
• Explain the use of Boolean algebra and adders.

What is a Logic Gate?

A logic gate is a tiny circuit that takes one or more binary inputs, each a 0 or a 1, and produces a single binary output according to a fixed logical rule. Gates are built from transistors and are the building blocks of every digital device; the ALU, memory and control circuits are all combinations of gates. To describe a gate, engineers use a truth table, a list of every input combination with its output. A two-input gate has 4 rows, a three-input gate 8.

The AND Gate

An AND gate has two or more inputs and its output is 1 only when all inputs are 1; if any input is 0, the output is 0. Its symbol is a flat-sided capital D with inputs on the left and the output on the right. The expression is Output = A AND B, also written as A. B or AB. A strong room that opens only when the correct code is entered AND a guard presses the button is a real-world AND because both must hold. Switches wired in series light a bulb only when both are on.

The OR Gate

An OR gate outputs 1 when at least one input is 1, and 0 only when all inputs are 0. Its symbol is the AND shape with a curved inlet, and the expression is Output = A OR B, written as A + B. An emergency light that comes on when switch A OR switch B is pressed is a real-world OR because one condition is enough. Switches wired in parallel light a bulb when either is closed.

The NOT Gate

A NOT gate has a single input and inverts it; input 0 gives output 1, and input 1 gives output 0. Its symbol is a triangle followed by a small bubble. The expression is Output = NOT A, written with a bar above the A. A fire alarm that stays silent while an override switch is ON sounds only when the override is NOT on.

The NAND and NOR Gates

NAND stands for NOT AND, which is an AND gate followed by an inverter, so its output is 0 only when all inputs are 1 and 1 in every other case; the expression is NOT (A AND B). NOR stands for NOT OR, which is an OR gate followed by an inverter whose output is 1 only when all inputs are 0; the expression is NOT (A OR B). NAND is called a universal gate because every other gate can be built from NAND gates alone; an AND gate is a NAND plus a NOT, and a NOT gate joins a NAND's inputs together.

The XOR and XNOR Gates

XOR stands for exclusive OR. Its output is 1 when the inputs differ and 0 when they are the same, so 0,1 and 1,0 give 1, while 0,0 and 1,1 give 0. Its symbol is the OR shape with an extra curved inlet, and the expression is A XOR B. XOR is essential in electronics; it builds the adders in the ALU, creates parity bits and appears in encryption. XNOR is the opposite; its output is 1 when the inputs are the same and 0 when they differ, meaning NOT (A XOR B); XNOR circuits compare two values for equality.

The table below compares all seven gates.

Boolean Algebra

Boolean algebra is the mathematics of 0 and 1. AND behaves like multiplication (0 x 1 = 0, 1 x 1 = 1), OR behaves like addition except that 1 + 1 = 1, and NOT is the complement. The order of operations is NOT first, then AND, then OR, unless brackets change it; in Output = A AND (B OR NOT C), the NOT C is done first, then the bracket, then the AND.

De Morgan's Laws

De Morgan's laws convert one logical form into another. The first law says NOT (A AND B) = (NOT A) OR (NOT B); the opposite of both being true is that at least one is false. The second law says NOT (A OR B) = (NOT A) AND (NOT B); the opposite of at least one being true is that both are false. The second law is exactly how a NOR gate behaves; the first lets a designer rebuild an AND circuit from OR and NOT gates. Prove either law by comparing both sides in a truth table.

The Half Adder

Combinational logic is a circuit whose output depends only on the present inputs, with no memory. A classic example is the half adder, which adds two bits, producing 0 + 0 = 0, 1 + 0 = 1, and 1 + 1 = 10, meaning 0 with a carry of 1. Its sum comes from an XOR gate and its carry from an AND gate, both fed by the same two inputs; the sum is A XOR B and the carry is A AND B. When both inputs are 1, XOR gives 0 and AND gives 1, which is exactly the 10.

The Full Adder

A half adder cannot handle a carry from a previous column, so real arithmetic uses a full adder with three inputs, namely A, B and a carry-in (Cin). Its sum is A XOR B XOR Cin, and its carry-out is (A AND B) OR (Cin AND (A XOR B)). The table below shows the eight combinations. To add multi-digit numbers, engineers chain one full adder per column, passing each carry-out to the next carry-in, exactly how the ALU adds.

Applications of Logic Gates

Logic gates appear throughout a computer. The ALU uses them for arithmetic, where XOR and AND gates build the adders, while other combinations carry out comparisons. Control circuits in the CPU, memory and keyboard decode signals and synchronise operations. Real-world systems work the same way; an ATM dispenses cash only when the card is valid AND the PIN is correct AND the balance is enough, and a home alarm sounds when the door OR the window sensor is triggered AND the system is armed. For any scenario, write the Boolean expression, build the truth table, and break the rule into AND, OR and NOT steps.

Practical Exercises

Test yourself with these problems before the Week 10 assessment.

State the output of AND, OR and NOT for inputs A = 1, B = 0.

Write the Boolean expression for output 1 only when A is 1 and B is 0.

Write the truth table for a NAND gate.

Draw the symbol for an XOR gate and describe its output rule.

Add 1 + 1 with a half adder and state the sum and carry.

Prove that NOT (A AND B) equals (NOT A) OR (NOT B).

Explain how a full adder is built from the same gates as a half adder.

Suggest a real gadget that uses an AND logic rule and justify your answer.

Digital Logic and Binary Signals

Digital logic is the branch of electronics that processes binary information, signals that are either 0 or 1, low or high. Every modern computer is built from circuits that follow these simple two-valued rules, and the building blocks of those circuits are called logic gates.

Inside the computer, a binary 1 is represented by a small voltage being present and a binary 0 by its absence. As signals travel along the wires of the CPU, gates read the incoming voltages, carry out a logical rule, and produce a single output voltage. Combining thousands of these simple decisions produces the arithmetic, comparison and control operations of a processor.

Because the rules are so few, they can be written precisely and tested. A logic gate is defined by its truth table, a table that lists every possible combination of inputs and the output each one produces. This week's periods build from the three basic gates, AND, OR and NOT, to the derived gates NAND, NOR and XOR, and then to full combinational circuits, exactly the path engineers follow when they design a chip.

Digital circuits work with two states, 0 and 1.

Logic gates read binary inputs and produce one binary output.

Combining gates builds the arithmetic and decision circuits of the CPU.

Truth tables record the behaviour of each gate for every input combination.

This overview connects Week 8's binary number systems with the ALU work from Week 1, showing how the 0s and 1s of data are actually manipulated inside the processor.

Gate Functions and Truth Tables at a Glance

The six gates can be grouped by how they behave. AND outputs 1 only when all inputs are 1. OR outputs 1 when at least one input is 1. NOT inverts a single input. NAND is the opposite of AND, outputting 0 only when all inputs are 1. NOR is the opposite of OR, outputting 1 only when all inputs are 0. XOR outputs 1 only when the two inputs differ.

A truth table is a complete check of a gate or a circuit. For two inputs A and B there are four combinations, 00, 01, 10 and 11, so a two-input truth table has four rows. The AND column reads 0, 0, 0, 1. The OR column reads 0, 1, 1, 1. NAND is the exact opposite of AND, 1, 1, 1, 0, while NOR is the opposite of OR, 1, 0, 0, 0. XOR reads 0, 1, 1, 0 because it is 1 only when the inputs differ.

To construct any truth table, a student lists every combination of inputs, then applies the gate rule row by row. This disciplined row by row method is exactly how combinational circuits are analysed in Period 3, and it is worth practising until it becomes automatic.

AND, output 1 only when every input is 1.

OR, output 1 when at least one input is 1.

NOT, single input inverted, 0 becomes 1 and 1 becomes 0.

NAND, output 0 only when every input is 1.

NOR, output 1 only when every input is 0.

XOR, output 1 when the inputs differ.

Combining Gates to Build Simple Circuits

Few real systems use a single gate. Engineers combine gates so that the output depends on several conditions at once, and a circuit built from connected gates is called a combinational logic circuit, because its output is a pure function of its present inputs.

A simple combined circuit can be designed step by step. Consider a system that rings a bell when a button is pressed at the same time as a key is turned. The button and the key feed an AND gate, and the result joins a second AND gate with a master switch, so the bell rings only when the master switch, the button and the key are all active. Each added gate makes the decision more selective.

Analysing such a circuit means writing the Boolean expression, building the truth table row by row, and checking it against the intended behaviour. Building the truth table for a three-input circuit produces eight rows, and the output column should match, row by row, the real-life rule the circuit is meant to enforce.

Real-World Applications of Logic Circuits

Logic circuits power the decisions of everyday machines. In a school, a door lock opens only if a correct code is entered AND a valid card is presented, an AND rule. An overhead fan in a laboratory turns on if the room is hot OR the air quality check fails, an OR rule. The alarm system from Period 3, Alarm equals D OR W AND A, is a real combination of OR and AND logic.

Inside the computer, the adder circuits of the ALU are built from XOR and AND gates, while comparison circuits decide whether one number is equal to another using XNOR logic. Even the most powerful processor is, at heart, billions of these simple gates wired together into one enormous logic circuit.

Combinational circuits combine gates so that output depends on several conditions.

Boolean expressions and truth tables let engineers verify a circuit before building it.

Alarm systems, door locks and the adder of the CPU are all built from combined gates.

This is the foundation for Week 10, where learners turn logic design into working programmes and simulations of digital circuits.

Practical Work

1. Draw the truth tables for AND, OR and NOT.
2. Write the truth table for the NAND gate.
3. Explain how a half adder adds two bits.
4. Simplify a simple Boolean expression.

Scenario-Based Questions

1. A student builds a circuit with two switches wired so a lamp turns on only when both switches are closed. Identify the logic gate that models this circuit and draw its truth table.
2. An engineer needs a gate that outputs 0 only when both inputs are 1. Identify the gate, write its Boolean expression and explain why NAND gates are called universal gates.
3. A student adds binary 1 + 1 using a half adder. State the sum and carry produced and explain why a full adder is needed when adding multi-bit numbers.
4. Using De Morgan's first law, prove that NOT (A AND B) equals (NOT A) OR (NOT B) by constructing a truth table for both expressions and comparing the output columns.
5. A security system activates an alarm when at least one of three sensors detects motion. Identify the type of logic gate used at each stage, write the Boolean expression for the output and explain why OR rather than AND is appropriate.
6. A computer technician explains that the ALU inside the CPU is built from logic gates. Name two specific operations the ALU performs and identify which gates are used to implement each operation.
7. A student is asked to design a circuit whose output is 1 only when inputs A and B are different. Identify the gate, write the Boolean expression and draw the truth table to verify the design.

Learning Objectives

• Define a network topology and name the main types.
• Compare bus, star, ring, mesh, tree and hybrid topologies.
• Describe the OSI and TCP/IP reference models.
• Classify networks as PAN, LAN, MAN or WAN.

What is a Network Topology?

A network topology is the arrangement of the devices in a network and the connections between them. The physical topology is the actual wiring, while the logical topology is the path data follows, and the two do not always match; the school lab is wired in a star, but the switch decides the logical route the data takes.

Bus Topology

In a bus topology all devices connect to a single central cable called the backbone. Data travels along the bus in both directions, and terminators at each end absorb the signal so it does not bounce back. Because all devices share one wire, only one can transmit at a time, so the whole bus is a single collision domain and two simultaneous transmissions clash. The bus is cheap and simple, but the backbone is a single point of failure; one cut takes the whole network offline.

Star Topology

In a star topology every device connects to a central switch or hub with its own cable, and data passes through the centre first. A switch forwards data only to the intended device, which is why stars are efficient and common in school labs, offices and homes. Its strength is isolation; one damaged cable affects only that device. Its weakness is the centre; if the switch fails, the whole network stops.

Ring Topology

In a ring topology each device connects to two neighbours to form a closed circle, and data travels in one direction, each station checking and then forwarding the signal. Older token ring networks circulated a token and allowed a device to transmit only while it held it, so no collisions occurred and access was fair. The ring is fragile because every device is part of the path; one broken device or cable breaks the loop. The idea survives in the dual fibre rings that protect telephone backbones.

Mesh Topology

In a mesh topology devices are joined by many direct links. A full mesh connects every device to every other, so four nodes need six cables (4 x 3 / 2), while a partial mesh connects only the key devices fully. Because data reroutes automatically when a link fails, the mesh is the most reliable but also the most expensive topology, so it is reserved for internet backbones and core bank networks.

Tree (Hierarchical) Topology

A tree, or hierarchical, topology joins several star networks onto one central backbone, combining bus and star. It branches like a family tree from a root down through switches to the workstations and scales well; a new department can be added as one star. A failure near the root brings down everything beneath it, so large campuses use a tree with one star per building.

Hybrid Topology

A hybrid topology combines two or more topologies in one network, such as stars inside offices joined by a mesh backbone. Real networks, including the internet, are almost always hybrids, because each section can use the layout that suits its cost and reliability needs.

The table below compares them.

Why Network Models Exist

Computers from different manufacturers use different hardware, so networking needed common rules called protocols. A network model organises the protocols into layers; each layer serves the layer above it and uses the layer below, so one layer can be upgraded without rewriting the whole system.

The OSI Reference Model

The Open Systems Interconnection (OSI) model, published by the ISO in 1984, is a seven-layer reference model for networks. A memory aid for the layers, from the bottom, is 'Please Do Not Throw Sausage Pizza Away'. When data is sent, it starts at the top layer and moves down, each layer wrapping it in its own information (encapsulation); the receiver unwraps it on the way back up.

The Seven Layers of the OSI Model

The Physical layer transmits raw bits as electrical signals, light pulses or radio waves. Common devices include hubs, repeaters and cables. The data unit is a bit. The analogy is the road that carries a letter.

The Data link layer groups bits into frames, moves them between neighbouring devices and checks for errors using MAC addresses. Common devices include switches. The data unit is a frame. The analogy is the local postman.

The Network layer routes packets across networks using IP addresses. Common devices include routers. The data unit is a packet. The analogy is the sorting centre that picks the next city.

The Transport layer delivers data end to end; TCP numbers segments so all arrive in order, UDP sends quickly without guarantees, and port numbers identify the receiving application. The data unit is a segment. The analogy is a guaranteed courier.

The Session layer opens, manages and closes a conversation between two applications. Common protocols include NetBIOS and RPC. The analogy is a telephone call.

The Presentation layer translates, compresses and encrypts data into a common format, such as ASCII or JPEG. The analogy is a translator.

The Application layer provides the services users actually use, such as browsing, email and file transfer. Common protocols include HTTP, HTTPS, FTP, SMTP and DNS. The analogy is the person writing the letter.

The table below summarises the layers.

The TCP/IP Model

The TCP/IP model is the practical model used on the internet and has four layers. The application layer merges the top three OSI layers (HTTP, HTTPS, FTP, SMTP, DNS); the transport layer holds TCP and UDP; the internet layer uses IP to address and route packets; and the network access layer covers the media such as Ethernet and Wi-Fi. When you open a website, data is wrapped layer by layer and unwrapped in reverse at the server.

The table below maps them to the OSI model.

VPN means virtual private network, giving secure remote access.

Comparing OSI and TCP/IP

OSI and TCP/IP describe the same journey in different detail. OSI has seven layers and is a reference model for teaching, standardising and troubleshooting, so it is not implemented in pure form. TCP/IP has four layers and is the working model built into routers and operating systems. TCP/IP merges the top three OSI layers into one application layer and the bottom two into one network access layer. Use OSI to name a layer or locate a fault in an exam; use TCP/IP to explain how the internet actually moves data.

The table below compares them.

Client-Server and Peer-to-Peer Models

In the client-server model a central server stores resources and manages data, while client computers request those resources. The web works this way (the browser is the client, the website is the server), and a school file server works the same way. Central control makes permissions, backups and security easy to manage, but the server is a single point of failure.

In the peer-to-peer model every computer can act as both client and server, with no central authority. Two home laptops can share files directly, which is cheap and easy, but control is hard; if no machine holds the master copy, data can be lost, and without central security each machine is a potential malware entry point. Organisations choose client-server; small home groups choose peer-to-peer.

The table below compares them.

Use this glossary while you revise.

Corporate Networks

A corporate network is a private network that connects computers, servers and devices within an organisation or across branches. Its main purposes are sharing resources, providing an intranet and supporting collaboration.

An intranet is a private network accessible only to authorised members of the organisation. It hosts internal websites, staff directories, memos and policy documents that should not be on the public internet.

Shared resources: printers, scanners, internet connections

Intranet: private websites and documents for staff only

Collaboration: shared calendars, email, video conferencing, instant messaging

In Nigeria, banks and telecom companies run large corporate networks connecting offices across many states. These use LAN, MAN and WAN building blocks with added security and central management.

Network Protocols in Business

A network protocol is a set of rules that controls how data is formatted, addressed, transmitted and received across a network. Without protocols, devices from different manufacturers cannot communicate.

TCP/IP: the foundation protocol of the internet; TCP breaks data into packets and guarantees delivery, IP handles addressing and routing

HTTP and HTTPS: used by web browsers to load websites; HTTPS adds encryption for secure transactions

FTP: transfers large files between computers

SMTP, POP3 and IMAP: handle email sending and receiving

DNS: translates domain names such as google.com into IP addresses

A typical school or business network uses all of these protocols simultaneously. Understanding them helps administrators troubleshoot and choose the right tools.

Network Security Measures and Threats

Network security is the set of practices and technologies used to protect data, devices and users from unauthorised access, data theft and malicious attacks.

Malware: viruses, worms and ransomware that damage files or lock systems

Phishing: fake emails or websites that trick users into revealing passwords

Unauthorised Wi-Fi access: connecting to weakly protected networks to steal data

Denial-of-service: overwhelming a server with fake requests so legitimate users cannot access it

Protection measures include firewalls, encryption, strong passwords and multi-factor authentication, and antivirus software. Good habits like not clicking suspicious links and never sharing passwords also help.

Nigerian organisations must comply with the Nigeria Data Protection Regulation (NDPR), which requires protection of citizens personal data.

Meaning and Uses of Networks

A computer network is two or more computers joined so that they can exchange data and share resources. The joining may be by cable or by radio. What is shared includes data, printers, storage space and an internet connection.

Networks are used in schools, banks, hospitals, government offices, shops and homes. A school network lets a teacher send a document to every computer in a laboratory. A bank network lets every branch reach the same account records.

Classes of Network

A personal area network covers a very small area, usually a few metres, such as a phone connected to a headset. A local area network covers one building or a small group of buildings, such as a school, and it is owned by one organisation.

A metropolitan area network covers a town or a city, joining several local area networks, such as the branches of a bank across a city. A wide area network covers a country or the world and is formed by joining many networks together.

The comparison is by area, and the area decides the equipment. The larger the area, the more expensive the equipment and the slower the data, because the signal travels further.

Network Devices

A modem converts a signal from the provider into a signal the computer can use, and back again. A router joins two or more networks and passes data between them, choosing the best route. A switch joins computers within one network and sends data only to the computer it is meant for, which reduces traffic.

A hub is an older device that sends data to every port, so every computer receives it. A switch is the modern replacement. A network interface card allows a computer to join a network, by cable or by radio.

A repeater strengthens a weakened signal. A bridge joins two networks of the same type. A gateway joins two networks of different types. An access point provides a wireless connection for devices within its range.

Topology

Topology is the shape in which the devices are connected. In a bus topology all the devices are connected to one central cable. It is cheap and uses little cable, but if the main cable breaks the whole network stops.

In a star topology every device has its own cable to a central switch. If one cable breaks, only that device is affected, which is why this is the common layout in schools. In a ring topology the devices are joined in a closed loop and the data passes in one direction around it.

In a mesh topology each device is connected to several others, so there is more than one route for the data. It is the most reliable and the most expensive. A hybrid topology combines more than one of these shapes.

Wired and Wireless Connections

A wired connection uses a cable and is fast, stable and not affected by walls. A wireless connection uses radio waves, so no cable is needed, but the signal weakens with distance and with obstacles.

Topology may be physical, showing the actual cables, or logical, showing the path the data takes. The two may differ, which is a point examined in network questions.

Practical Work

1. Draw a star and a mesh topology and label each device.
2. Use a table to compare the strengths and weaknesses of the topologies.
3. List the seven OSI layers in order.
4. Classify five networks by the area each covers.

Scenario-Based Questions

1. A school lab is wired in a star. Explain why a cut cable affects only one computer.
2. A company needs the most reliable network and will pay for it. Recommend a topology.
3. Explain why real networks such as the internet are almost always hybrid.
4. Explain why the OSI model is arranged in layers.

Learning Objectives

• Describe the internet and the services it provides.
• Explain how data travels across the internet.
• Describe online safety, ethics and security.
• Apply rules for safe and responsible online behaviour.

What the Internet Is

The internet is a global network of networks. It began as a research project called the ARPANET, which connected universities in the United States. Other networks joined over the years, and the result is a system with no central control and no single owner.

The internet is not the same as the World Wide Web. The internet is the network that carries data, and the web is one service running on it, made of linked pages. Email, file transfer and voice calls also run on the internet without being part of the web.

The internet and the web are not the same thing. The web is one service on the internet.

The internet has no central owner or control, so no single organisation can switch it off.

How Data Travels

Data is split into small pieces called packets. Each packet carries the addresses of the sender and the receiver and a part of the data. Packets travel along any available route and may take different routes, and they are reassembled in the correct order when they arrive.

The rules that govern this are called protocols. The main set is TCP/IP, which governs how data is addressed and routed. HTTP governs the web, SMTP governs sending mail and FTP governs file transfer.

Data travels through several media. Twisted pair copper cable carries it inside a building. Fibre optic cable carries it as light over long distances at very high speed. Radio waves carry it between buildings and to mobile phones. Satellites carry it between countries.

The amount of data a connection can carry at one time is its bandwidth. A wider bandwidth carries more data in the same period, which is why a fibre connection feels faster than a mobile connection.

Bandwidth is the amount of data that can be carried at one time, not the speed of one file alone.

Broadband means a connection that carries a large amount of data.

Phishing means a method of tricking a user into giving away details.

Services on the Internet

The services are grouped into communication, information and transaction. Communication services include email, chat, forums, social networks and video calls. Information services include the web, search engines, digital libraries and online encyclopaedias.

Transaction services include online banking, shopping, paying bills, registering for examinations and submitting tax returns. Government services in Nigeria, such as the national identification number and the tax filing platform, are reached this way.

Cloud services store files on servers rather than on the computer, so the files can be reached from any device with an internet connection. Collaboration tools allow several people to work on the same file at the same time.

A modem does not create the internet connection. It converts the signal so that the computer can use it.

Cloud storage means storage held on remote servers and reached over the internet.

Access and the Local Situation

Access is provided by an internet service provider, which sells a connection and gives an address to the subscriber. Access may be by cable, by fixed radio, by mobile data or by satellite, and the choice affects the speed, the cost and the reliability.

In Nigeria, schools and homes use a mixture of these. Many schools depend on a single connection shared by all the computers in a laboratory, so one user downloading a large file slows the work of everyone else.

A school network should be planned with the number of users in mind, because a connection adequate for five users is not adequate for thirty.

Web Technologies

The web works through addresses and browsers. An address beginning with https is encrypted, which means the data is scrambled in transit and cannot easily be read by anyone who intercepts it. A browser requests a page, the server sends it and the browser displays it.

A page that is too large takes long to load, which matters in a school where the connection is shared. Keeping pages light is therefore a practical concern as well as a technical one.

Personal Safety Online

Anything posted online can be copied and shared, and a post cannot be fully withdrawn. The rule to follow is to post nothing that would embarrass you if it appeared on a poster in school. This covers photographs, messages and reactions to other people's posts.

Personal details must be kept private. These include a home address, a phone number, a bank account, a password and the name of the school a child attends. A genuine organisation never asks for a password, so a message that does so is almost certainly an attack.

Personal safety also covers contacts. Accepting a request from a stranger gives that person access to your profile and your list of contacts. Meeting someone first met online must never happen without a parent or teacher present.

Cyber safety means the practices that protect a person and a device when online.

Personal information means details that identify a person, such as an address or a password.

Security of the Computer

A virus is a program written to damage a computer or the data on it. A worm spreads across a network by itself. A trojan looks useful but carries a harmful part. Spyware collects information without the user knowing. Ransomware locks files and demands a payment to release them.

Protection is by prevention. An up to date antivirus program checks files and removes anything harmful. A firewall blocks unwanted connections. Strong passwords of at least eight characters with a mixture of letters, numbers and symbols are much harder to guess, and a different password is used for each important account.

Software is updated because updates repair faults that attackers can use. An operating system or a browser that is no longer supported will eventually be attacked successfully, so a device that cannot be updated should be replaced rather than kept.

Cyber Crime and Cyber Ethics

Cyber crime is any crime committed using a computer or a network. Examples include accessing an account without permission, copying paid software, spreading a virus deliberately, forging a document and carrying out fraud online. Most countries, including Nigeria, have laws that make these offences punishable.

Cyber ethics is the correct use of information and communication technology. It means respecting the rights of others, respecting copyright, respecting privacy and not using technology to harm anyone.

Copyright is the right of the owner to control the use of a work. Copying a textbook, a song or an image without permission breaks copyright. Quoting a short part with the source named is acceptable. Plagiarism is presenting the work of another as one's own, whether or not copyright was involved.

Healthy and Responsible Use

Time spent online must be balanced. A fixed daily limit agreed with a parent or teacher prevents the loss of sleep and the neglect of study that heavy use causes. Sitting at a computer for hours without a break harms the eyes, the back and the wrists.

Content must be chosen with care, because material found online is not checked for accuracy or suitability by anyone. Parents and teachers should know which sites are suitable for the age group, and filtering software helps where a school can install it.

Practical Work

1. List five services of the internet and one use of each.
2. Describe what happens when a web page is requested.
3. Write five rules of safe online behaviour.
4. Explain why a strong password matters.

Scenario-Based Questions

1. A learner receives a message asking for a bank password. Explain what to do.
2. Explain why the same information may be untrustworthy even on a popular site.
3. Describe two ways to keep an account secure.
4. Explain why personal information should not be shared publicly.

Learning Objectives

• Define a database and state why databases are used.
• Describe the parts of a database.
• Distinguish between a table, a record and a field.
• Create, sort and filter a table in a database program.

Meaning and Reason for Databases

A database is an organised collection of related data stored so that it can be searched, sorted and retrieved quickly. A file system stores data in separate files, which leads to duplication and to data that disagrees with itself. A database stores the data once in a controlled structure.

A school keeps a register of pupils. In files, each pupil would have a separate file, and a change of address would have to be made in several places. In a database there is one pupil record, so the change is made once and every report that uses it is correct.

A database is used when there is a large amount of related data that must be searched quickly or reported on in different ways. Schools, banks, hospitals, shops and government offices all use databases.

Parts of a Database

A database system has three parts. The database itself is the collection of stored data. Database software is the application used to enter, search and report on the data. The hardware is the machine and the storage that holds it.

Within the database, data is held in tables. A table holds one kind of record, such as all the pupils or all the staff. A record is one row and holds the fields of one item. A field is one column and holds one kind of information about every record, such as the surname of every pupil.

Each table has a key. The primary key is the field or combination of fields that makes every record unique, and no two records may share the same key. A pupil number makes a good primary key because it is unique and does not change, while a name does not, because two pupils may have the same name.

A table and a record are not the same. A table holds many records, and a record is one row.

A field is not a column label only. The label is the field name, while the field holds the value in each row.

A primary key must be unique, so a name is a poor choice because two people may share it.

Keys, Relationships and Design

A foreign key is a field in one table that refers to the primary key of another table, and the link is called a relationship. A pupil table holds the name and address, an marks table holds the scores, and the pupil number links them.

The design is called normalisation. Splitting the data so that each fact is stored once avoids repetition. The pupil table holds the address once and the marks table holds the scores, and neither repeats the other. This is called first normal form, and the goal is that a fact is entered once and used everywhere.

A relationship may be one to one, where each record in the first table matches exactly one in the second, or one to many, where one record matches many in the second. One pupil has many results, so that is a one to many relationship.

Validation means checking data as it is entered.

Redundancy means the same fact stored more than once.

Using a Database Program

A database program is used to create a table, define the fields and their data types, and then enter the records. The data type is set for each field, such as text, number or date, and it decides what may be entered.

Records are sorted by choosing a field and the sort order, which arranges the records alphabetically or by value. Filtering shows only the records that meet a stated condition, such as all the pupils in a given class, while the rest are hidden but not deleted.

A search finds a particular value. A report is a formatted output produced from the data, such as a list of pupils in a class or a record of attendance. Reports are generated from the stored data, so they are up to date without being typed.

Filtering hides records without deleting them, so a filtered result is not a reduced database.

Advantages and Precautions

The advantages of a database are that data is stored once, searches are fast, several users may work with the same data at once, security can control who sees what, and reports can be produced in any required format.

Precautions are needed because a database holds a great deal in one place. Access is given only to those who need it, a password protects it, a backup copy is kept separately, and the data is validated on entry so that a date of birth cannot be entered as a word.

Practical Work

1. Create a database with one table of pupils holding the fields pupil number, surname, forename, class and date of birth.
2. Set the data type of each field and set the pupil number as the primary key.
3. Enter ten records, then sort the table by surname and confirm the order.
4. Use a filter to show only the pupils in a given class and record the number shown.
5. Create a second table of results holding the pupil number and three scores, and link it to the first table using the pupil number.
6. Produce a report listing the pupils in one class with their scores.

Scenario-Based Questions

1. Explain why storing pupil records in separate files leads to errors that a database avoids.
2. A school wants to use names as the primary key of a pupil table. Give two reasons this is a poor choice.
3. Explain the difference between a field and a record, using a library catalogue as an example.
4. Describe how splitting the address from the marks table reduces redundancy.
5. Explain what a filter does and state what it does not do.
6. A database holds confidential results. Explain two precautions that should be applied.
7. Explain the difference between a one to many relationship and a many to many relationship.

Learning Objectives

• Use mail merge and templates in a word processor.
• Use spreadsheet formulas and functions.
• Apply advanced features in presentations.
• Combine tools to integrate and share work.

Mail Merge and Templates

Mail merge is a word processing feature that allows you to create one main document and automatically generate multiple personalised copies using data from a list or database. It is widely used in schools, offices, banks and businesses. The three components of a mail merge are a main document, a data source and merge fields. The main document is the letter or certificate template containing blank fields. The data source is a list of names, addresses and other details, often stored in a spreadsheet. The merge fields are placeholders in the main document where the data is inserted. To create a mail merge, prepare the data source, open the word processor and create the main document, insert merge fields where personalised data should appear, connect the document to the data source, preview the merged documents, and then print or save them.

A template is a pre-designed document with a fixed layout, fonts, colours and placeholder text. Templates save time and ensure consistency across documents. Common templates include school report cards, certificates, letterheads, invoice forms and newsletters. Most word processors and presentation tools come with built-in templates, and users can also create and save their own custom templates. For example, a school secretary who must send 150 appointment letters to new staff can create one template letter, set up a spreadsheet with the staff names and details, and use mail merge to produce all 150 personalised letters in minutes rather than in days.

Spreadsheet Formulas, Functions and Pivot Tables

A formula in a spreadsheet starts with an equals sign (=) and uses cell references to perform calculations. For example, =A1 + B1 adds the values in cells A1 and B1. Formulas can use the arithmetic operators for addition, subtraction, multiplication and division, and they can reference any cell on the sheet. A function is a built-in formula that performs a specific task. Common functions include SUM, which adds all the numbers in a range, AVERAGE, which finds the arithmetic mean, COUNT, which counts the cells containing numbers, MAX, which returns the largest value, MIN, which returns the smallest value, and IF, which returns one result when a condition is true and another when it is false. Cell references can be relative, so A1 changes when copied to another cell, or absolute, so $A$1 stays fixed when copied. Understanding this distinction is important when copying formulas across rows and columns.

A pivot table is a tool that summarises large amounts of data into a compact report. It can group data, calculate totals and averages, count entries and create cross-tabulations without changing the original data. For example, if a school has 500 rows of test results, a pivot table can quickly show the average score per subject or the number of students per class. To create a pivot table, select the data range, insert a pivot table, drag fields into the rows, columns and values areas, choose the summary function, and then format and filter the table as needed.

Advanced Presentations and Productivity Suites

Modern presentation software offers features beyond simply putting text on slides. A slide master controls the default layout, fonts, colours and logo placement for all slides, ensuring consistency. Transitions are the visual effects that play between slides, such as fade, wipe or push. Animations are effects applied to individual elements on a slide, such as appear, fly in or emphasis. Speaker notes are private notes visible only to the presenter during the slideshow. The golden rule of presentation design is clarity, meaning that every visual element should support the message rather than compete with it.

Google Workspace and Microsoft 365 are the two most widely used productivity suites. Google Workspace includes Google Docs for word processing, Google Sheets for spreadsheets, Google Slides for presentations and Gmail for email, all cloud-based, with free personal accounts and real-time collaboration in a browser. Microsoft 365 includes Word, Excel, PowerPoint and Outlook, and is subscription-based, with full offline access through desktop apps and more advanced features. Both suites are widely used in Nigerian schools and businesses. Google Workspace is popular in education because of its free tier and easy collaboration, while Microsoft 365 is preferred in many offices for its advanced features and offline capability. Productivity tools are used daily for school administration, such as recording learner scores, for business communication, such as writing memos, for marketing, such as creating presentations, for event planning, such as building budgets and printing personalised invitations, for data analysis with pivot tables, and for remote teamwork with real-time co-editing from different locations.

Advanced Spreadsheet Skills

Every value in a spreadsheet lives in a cell, and each cell has a unique address made from its column letter and row number, such as A1 or C5. Formulas begin with an equals sign and perform calculations using these addresses. A formula that adds the values in cells B2 and C2 produces the result automatically, and if the values change, the result updates at once. This automatic recalculation makes spreadsheets far more useful than hand-written tables.

Charts turn spreadsheet data into pictures such as bar charts, line graphs and pie charts. A pie chart shows proportions, a bar chart compares groups, and a line graph shows trends over time. Charts make it much easier for an audience to understand large sets of numbers at a glance. Choosing the right chart for the data is a key spreadsheet skill used in business reports and school projects.

Advanced Word Processing and Presentation Features

A template is a pre-designed file with a fixed layout, fonts and colours that can be reused for many documents with the same style, such as school report cards, invoices or certificates. Using a template keeps documents consistent and saves the time of rebuilding the layout each time.

In presentation software, transitions control how one slide changes into the next, for example a fade or a slide-in effect. Animations control how individual elements on a slide appear, such as text appearing one line at a time or an image flying in. A slide master sets the theme, fonts and layout for the whole presentation at once, so every slide inherits the same professional look. The golden rule is clarity, every effect should support the message rather than distract.

Integration and Collaboration Tools

Modern productivity suites integrate tools so that data flows between word processing, spreadsheets and presentations. A chart made in a spreadsheet can be placed inside a report, and a table in a slide can stay linked to its source data. Integration saves time and keeps information consistent across different documents.

Collaboration tools allow teams to share documents with chosen people, co-author in real time and keep a full history of every change. The owner sets permissions that control who can view, comment or edit a document. Real-time co-authoring shows each person working on the file, and version history lets a team restore an earlier version if a mistake is made. Cloud office suites such as Google Workspace and Microsoft 365 make this possible from any device with an internet connection.

Formulas and References

A formula begins with an equals sign and may contain values, cell addresses, operators and functions. The result is shown in the cell and the formula is shown in the formula bar, so one set of figures can produce many results without retyping.

A relative reference changes when the formula is copied, so the formula in cell D2 written as equals B2 times C2 becomes equals B3 times C3 when it is dragged down one row. An absolute reference does not change and is written with dollar signs, as in $B$2. A mixed reference fixes one part only, as in B$2 or $B2.

An absolute reference is used for a constant that every calculation shares, such as a rate of tax. If the rate changes, changing the one cell updates every calculation, which is far better than editing every formula.

Statistical Functions

SUM adds the values in a range. AVERAGE gives the mean. MAX and MIN give the highest and the lowest value. COUNT counts the cells that hold numbers and COUNTA counts all the cells that are not empty.

ROUND rounds a value to a stated number of decimal places. MEDIAN gives the middle value in a sorted list and MODE gives the value that occurs most often. These functions are used when a report needs a figure that is fair to every learner, since one very high mark can distort a mean.

SUMIF adds the values that meet a stated condition and COUNTIF counts the values that meet a condition. Together they answer questions such as how many pupils scored above 50 and what is the total of the marks of those who scored below 40.

Logical, Text and Date Functions

IF tests a condition and gives one value when it is true and another when it is false. The condition is written first, then the value for true, then the value for false. A nested IF tests a second condition when the first fails.

AND and OR test several conditions at once and return true or false. NOT reverses a single condition. These classify pupils, for example as passing when the mark is at least 50.

Text functions work with the words in a cell. LEFT and RIGHT take characters from the ends of a word, LEN counts the characters, UPPER and LOWER change the case, CONCATENATE joins values into one cell and TRIM removes extra spaces.

Date functions work with dates. TODAY gives the current date and NOW gives the date and the time. DATE builds a date from three numbers. Two date arguments can be subtracted to find the number of days between two events.

Lookup Functions

A lookup function searches a table for a value and returns something from the same row. VLOOKUP searches down the first column of a table and returns a value from a chosen column. The arguments are the value to search for, the range of the table, the column to return from, and whether the table is sorted exactly.

HLOOKUP works in the same way but searches across the first row. INDEX returns the value at a given row and column of a range, and MATCH returns the position of a value within a range. MATCH combined with INDEX is more flexible than a single lookup.

A lookup is only correct if the first column of the table is sorted. An unsorted table gives an incorrect answer with no warning, so the sort is checked before the lookup is built.

Building a Summary Worksheet

A summary worksheet collects the results from the other worksheets. The number of pupils is taken from the count function, the mean from the average function, the highest and the lowest from the maximum and minimum functions, and the number passing from a count if function.

The summary refers to the data worksheet by writing its name before the range, as in the sum of Scores from B2 to B41. This is a cell reference applied to a whole worksheet, and it is what allows the summary to be built from the data rather than from retyped figures.

A summary is only worth building if it updates. If the figures are retyped by hand each time the data changes, the summary soon disagrees with the detail worksheets.

Practical Work

1. Create a mail merge letter for five recipients.
2. Write spreadsheet formulas for sum, average and highest value.
3. Add a chart to a slide and format its title.
4. Export a document to a portable format and share it.

Scenario-Based Questions

1. A school must send the same letter to 200 parents. Explain how mail merge helps.
2. A class list of scores must be summarised. Describe the functions you would use.
3. Explain why a chart helps an audience understand data.
4. Explain one benefit of sharing a document online.

Learning Objectives

• Revise all topics of the term.
• Consolidate architecture, storage and operating systems.
• Practise number systems, logic and productivity tools.
• Prepare for the end of term examination.

Review of Architecture, Memory and Storage

A computer follows the input, process and output model. The processor fetches, decodes and executes instructions, and the system bus carries data, addresses and control signals between the parts.

Memory is arranged in a hierarchy. Cache is small and fast, RAM is larger and temporary, and secondary storage is permanent. Magnetic, optical and solid state devices hold data in different ways, and cloud storage keeps data on remote servers.

An operating system manages the processor, the memory, the storage and the devices, and it provides the interface the user works with. Software is used under a licence, and using the wrong licence is illegal.

Review of Number Systems and Logic

A number system is built on a base. Binary is base 2, octal is base 8 and hexadecimal is base 16. The value of a digit depends on its place value.

A logic gate takes one or more bits and gives one bit. The AND, OR and NOT gates are the basic gates, and the NAND, NOR and XOR gates are built from them. Every gate can be shown in a truth table, and gates combine to add and compare numbers.

Review of Networks and the Internet

A network topology is the arrangement of devices and links. The main types are bus, star, ring, mesh, tree and hybrid. Networks are also classified by area as PAN, LAN, MAN and WAN.

The internet is a global network of networks. It carries the web, email, messaging and streaming. Data moves in packets using the protocol family TCP/IP.

Online safety matters. Passwords are kept strong and private, personal information is protected, and messages that ask for details are checked before they are trusted.

Review of Productivity Tools

A word processor uses mail merge and templates to produce many personalised documents from one letter and a list. A spreadsheet uses formulas and functions to calculate, and a pivot table to summarise. A presentation uses advanced features to communicate clearly.

The tools work together. A table can move from a spreadsheet into a word processor, and a chart can move into a slide.

Practical Work

1. Convert 45 to binary and to hexadecimal from memory.
2. Draw the truth tables for AND, OR and NOT.
3. List the seven OSI layers in order.
4. Write one spreadsheet formula and explain what it does.

Scenario-Based Questions

1. Explain how you would revise ten weeks of work in four evenings.
2. Explain why reading notes once is a weak method of revision and give a better method.
3. A learner says RAM and ROM are the same. Explain the difference.
4. A learner mixes up a star and a mesh topology. Explain the difference.
5. Explain why software licensing matters for a school.

Examination and Continuous Assessment Practice

These questions are taken from the First Term examination and Continuous Assessment papers for this class. Answer them in full sentences.

1. A factory needs a system that responds to a sensor within milliseconds, and a school needs one that runs on free software. Name the types of operating system, and compare the common operating systems with their strengths.
2. (a) Define Computer Software and classify it into its main categories, giving two examples of each. (b) Explain the primary functions of an Operating System. (c) A software application installer has a file size of 24 Megabits (Mb). Convert this file size into Megabytes (MB) and further into Kilobytes (KB). Show all steps.
3. (a) Define the Central Processing Unit (CPU) and explain the specific roles of its two main components (ALU and CU). (b) Explain the concepts of Cold Booting and Warm Booting. (c) A system diagnostic log file consumes 5,120 Bytes of storage space. Convert this file size into Kilobytes (KB) and calculate how many bits that file occupies. Show all workings.
4. (a) What is a Spreadsheet Package? Give two popular examples. (b) Explain the importance of the equal sign (=) when entering formulas in a spreadsheet and describe the difference between a row and a column. (c) Perform the following storage scale conversions, showing all intermediate steps: (i) Convert 1.5 Terabytes (TB) into Gigabytes (GB). (ii) Convert 2,048 Megabytes (MB) into Gigabytes (GB). (iii) Arrange the following storage capacities in ascending order: 8,192 Bits, 1 MB, 512 KB, 2 GB.
5. (a) Define Computer Security Threats (Malware) and list three (3) examples of malicious software. (b) Explain the roles of Antivirus software and Firewalls in safeguarding computer systems. (c) If a network data transmission channel transfers data at a speed of 8 Megabits per second (Mbps), calculate how many Megabytes (MB) of data are transferred in 10 seconds. Show your workings.
6. A learner asks what computer architecture means and why one model is taught more than any other. Define computer architecture, describe the Von Neumann architecture, and explain why the model matters.
7. A computer loses an unsaved document when it is switched off, and it starts up correctly every morning. Explain main memory, RAM and ROM, and state the difference between DRAM and SRAM.
8. A computer's CPU is slowed by frequent trips to memory, and its owner notices that only 4 GB of an installed 8 GB is being used. Explain cache memory and the memory hierarchy, and explain the address limit.

Learning Objectives

• Answer every section of the examination paper.
• Complete the practical task accurately within the time allowed.
• Apply the conventions of the topics taught this term.
• Analyse the result and plan the Second Term revision.

Before the Examination

Arrive early and confirm that the practical computers are working. Lay out two pens, a pencil, an eraser, a ruler and the identification card. Read the whole instruction sheet before touching the keyboard and note the required file name, folder and format.

A file saved under the wrong name or in the wrong folder is treated as missing.

During the Written Paper

The paper will include objective questions that test single facts, names and classifications. It will also include short answer questions that test definitions, differences and short explanations.

Answer every question. Begin with the ones you are sure of. In a classification question, write the group before each item. In a list question, number the items so that each can be marked. Show the working for any conversion.

A conversion answer without working may be marked wrong even when the result is correct.

A program that runs is not necessarily correct, because a logic error gives no message.

During the Practical Paper

Work in the order given. Create the file, enter the content, apply the required formatting or function, then save with the exact name in the exact folder. Save at each stage rather than only at the end.

Check the finished file against the task before the time ends: the required sheet, database or program exists, the required functions or statements have been used, and the file name matches the instruction.

After the Examination

The marked script is analysed by counting the marks lost on each question. A question that most learners missed identifies a topic to reteught in the Second Term.

The Second Term begins with revision of the weak topics and then moves to new work, which continues with programming, databases and networks.

Marks are lost on the instruction more often than on the topic, so the instruction is read before the work begins.

Practical Work

1. Read the whole instruction sheet before starting the practical task.
2. Note the required file name, folder, format and language before typing.
3. Save the file at each stage of the task.
4. Test a program with at least three sets of data, including a zero.
5. Check the finished file against every item in the instruction before the time ends.
6. Note the topics that felt weakest for the Second Term revision plan.

Scenario-Based Questions

1. Explain why most marks in a practical examination are lost on the instruction rather than on the skill.
2. Describe how you would check a finished database against the practical instruction.
3. A candidate has eight minutes left and the file has not been saved. Explain the priority order.
4. Explain how the result of the examination is used to plan the Second Term work.
5. Explain why a conversion answer should show the working.
6. Explain the difference between an objective question and an essay question.
7. A program gives a result that is too high on every test case. Explain what this suggests and how you would find it.
8. ODELAMI

First Term Examination Practice Questions

These questions are taken from the First Term examination and Continuous Assessment papers for this class. Answer them in full sentences.

1. (a) What is a Word Processor? Mention three (3) practical uses of word processing software in modern offices. (b) Explain the purpose of text formatting features such as Bold, Italic, and Underline. (c) A plain text document consists of 4,096 characters (where 1 character = 1 Byte). Calculate its exact size in Kilobytes (KB) and determine how many bits are contained in that file. Show workings.
2. (a) Define Computer Security Threats (Malware) and list three (3) examples of malicious software. (b) Explain the roles of Antivirus software and Firewalls in safeguarding computer systems. (c) If a network data transmission channel transfers data at a speed of 8 Megabits per second (Mbps), calculate how many Megabytes (MB) of data are transferred in 10 seconds. Show your workings.
3. (a) Define Computer Software and classify it into its main categories, giving two examples of each. (b) Explain the primary functions of an Operating System. (c) A software application installer has a file size of 24 Megabits (Mb). Convert this file size into Megabytes (MB) and further into Kilobytes (KB). Show all steps.
4. (a) Define the Central Processing Unit (CPU) and explain the specific roles of its two main components (ALU and CU). (b) Explain the concepts of Cold Booting and Warm Booting. (c) A system diagnostic log file consumes 5,120 Bytes of storage space. Convert this file size into Kilobytes (KB) and calculate how many bits that file occupies. Show all workings.
5. (a) What is a Spreadsheet Package? Give two popular examples. (b) Explain the importance of the equal sign (=) when entering formulas in a spreadsheet and describe the difference between a row and a column. (c) Perform the following storage scale conversions, showing all intermediate steps: (i) Convert 1.5 Terabytes (TB) into Gigabytes (GB). (ii) Convert 2,048 Megabytes (MB) into Gigabytes (GB). (iii) Arrange the following storage capacities in ascending order: 8,192 Bits, 1 MB, 512 KB, 2 GB.
6. (a) Define a Computer Network and list three (3) classifications based on geographical coverage (LAN, MAN, WAN). (b) State two (2) reasons why networking computers is essential for resource sharing and communication in schools. (c) State two (2) differences between a Web Browser and a Search Engine.