SS 2 First Term

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.