SS 1 First Term

Learning Objectives

• State the role of the operating system.
• Describe file management and the types of interface.
• Explain the booting process.
• Name the main types of operating system.

Role of the Operating System

An operating system (OS) is system software that manages all the hardware and software resources of a computer. It acts as an intermediary between the user, the application software, and the physical hardware. Without an OS, every user would need to write instructions directly to each hardware device, which would be extremely difficult and inefficient.

The OS performs four main management functions, namely process management, memory management, file management, and device management. Think of the OS as the headmaster of a school. The headmaster does not teach every class directly, but assigns teachers (programs) to classrooms (memory), ensures the timetable (process scheduling) runs smoothly, manages the school's records (files), and makes sure the equipment (devices) is available when needed.

Process management involves deciding which program gets CPU time and for how long. Modern operating systems support multitasking, which means they can switch between processes so quickly that they appear to run at the same time, even on a single-core CPU.

Memory management involves allocating RAM to each running process and reclaiming it when the process finishes. If too many programs are running and RAM is full, the OS may use virtual memory, temporarily moving some data to the hard drive to free up RAM.

File Management, Interfaces, and Common Operating Systems

The OS organises data on storage devices using a file system. Files are stored in folders (directories) in a hierarchical structure. The OS keeps track of where each file is stored on the hard drive using a file allocation table or similar structure. It allows users to create, open, rename, move, and delete files through a file explorer or finder.

Most modern operating systems provide both a graphical user interface (GUI) for everyday tasks and a command-line interface (CLI) for advanced tasks. A GUI uses visual windows, icons, and menus that you can click. A CLI requires typing text commands. GUIs are easy for beginners, visual and intuitive. CLIs are faster for experienced users and use fewer resources.

Common desktop operating systems include Windows (Microsoft), macOS (Apple), and Linux (open-source). Common mobile operating systems include Android (Google) and iOS (Apple). Windows is used on most school and office computers. macOS is used on Apple Macs. Linux is used on servers, some schools, and by developers. Android is used on Samsung, Tecno, and Infinix phones. iOS is used on iPhones and iPads.

The Booting Process

When a computer is powered on, it follows a fixed sequence to load the operating system. First, electricity flows to the motherboard and components (power on). Second, the BIOS/UEFI firmware performs a Power-On Self-Test (POST) to check that hardware is working correctly. Third, the BIOS/UEFI locates the boot device (HDD or SSD) and loads the bootloader. Fourth, the bootloader loads the operating system kernel into RAM. Fifth, the kernel starts essential services such as the file system, network, and display. Sixth, the OS loads the desktop, login screen, or home screen.

If the POST finds a hardware problem, such as no keyboard or faulty RAM, it displays an error message or beep codes before the OS loads. A cold boot starts from completely off and performs a full POST and OS load. A warm boot restarts the computer and skips some checks for speed.

Booting means the process of starting a computer and loading the operating system.

The Functions of an Operating System

An operating system carries out five essential functions that together let a computer work safely and smoothly. It manages processes, memory, files and devices, and it also enforces security. Each function addresses a different resource, and the OS coordinates all of them at once.

Process management decides which running programme, called a process, gets the CPU's attention and for how long. Memory management allocates RAM to each running process so that every programme gets the space it needs, and reclaims the space when a process ends. File management organises data on storage devices using folders and a file system, so files can be saved, located and retrieved by name.

Device management controls the hardware connected to the computer, such as keyboards, printers and storage drives, by loading the correct drivers and passing data between the device and the running programmes. Security management protects the system from unauthorised access through user accounts, passwords and permissions, and it restricts what each user is allowed to do.

Process management, scheduling which programme uses the CPU and when.

Memory management, allocating and reclaiming RAM for running processes.

File management, organising, storing and retrieving data in folders.

Device management, controlling hardware through device drivers.

Security management, protecting the system with accounts, passwords and permissions.

Together these five functions are the reason the OS is described as a manager. It does not do the user's work directly, but it makes sure every part of the system does its own job at the right time, in the right order and in safety.

Types of Operating Systems

Operating systems are designed for different kinds of devices and different jobs. The main types are desktop operating systems, server operating systems, mobile operating systems and real-time operating systems.

Desktop operating systems run on personal computers, laptops and many school machines. The most common are Microsoft Windows, Apple macOS and the open-source Linux. Server operating systems run on server computers that serve many users at once, such as Linux distributions and Microsoft Windows Server, and they are built for reliability, security and running for long periods without restarts.

Mobile operating systems run on smartphones and tablets, and two dominate the Nigerian market, Google's Android, used on phones from brands such as Tecno, Infinix, Samsung and Nokia, and Apple's iOS, used on iPhone devices. Real-time operating systems respond to inputs within a fixed time limit, and they are used in machines that must react instantly, such as car braking systems, medical monitors and industrial machines.

Desktop OS, Windows, macOS and Linux for personal computers.

Server OS, Linux distributions and Windows Server for serving many users.

Mobile OS, Android and iOS for smartphones and tablets.

Real-time OS, used where the system must react within a fixed time, as in car brakes and medical monitors.

Choosing the right operating system depends on the job, and many Nigerian homes now hold several types at once, a Windows desktop for school work, an Android phone for browsing and a smart television with its own embedded system.

User Interfaces, CLI and GUI

A user interface is the part of the operating system a person talks to. Two families dominate, the command-line interface, CLI, where the user types text commands, and the graphical user interface, GUI, where the user clicks icons, buttons and menus.

The CLI is powerful, fast for repetitive tasks and uses very little memory, but the user must remember exact commands. The GUI is easier to learn because pictures replace commands, and it is the interface most everyday users prefer. Since Period 2 compared these two interfaces, this section looks at how they fit together in modern systems.

Modern desktop operating systems offer both. Windows provides the Explorer GUI alongside the Command Prompt and PowerShell, while macOS offers the Finder GUI with the Terminal, and most Linux systems rely heavily on the shell. Users move from the GUI to the CLI when they need precise control or automation.

Accessibility in Modern Interfaces

Accessibility means making the interface usable by people with different abilities. Modern operating systems provide features such as screen readers that speak the on-screen text aloud, high-contrast themes for low vision, magnifiers that enlarge parts of the screen, and speech recognition that turns a spoken word into typing.

For users with motor difficulties, the OS can slow the mouse speed, enable sticky keys that let one key be used one at a time, and accept eye or head tracking on some devices. Accessibility settings turn a standard computer into a tool nearly everyone can operate, and schools in Nigeria can enable these features free of charge on the machines they already own.

Screen readers speak on-screen text aloud for users with low vision.

High contrast and magnifier tools enlarge and clarify the display.

Speech recognition turns spoken words into typed text.

Sticky keys and slower mouse speeds help users with motor difficulties.

Accessibility is not a special extra; it is part of good operating system design, and these features benefit every user, such as when a learner reads text aloud or works with a small screen.

Practical Work

1. List five functions of an operating system.
2. Draw a table comparing a command line and a graphical interface.
3. Describe the steps that happen when a computer is switched on.
4. Name three operating systems and one device that uses each.

Scenario-Based Questions

1. A lab manager opens many programs at once until all the RAM is full. Predict what the operating system does to prevent a crash, and why the machine slows down, using memory management and virtual memory.
2. A beginner wants an easy machine, while a network engineer needs speed for repeated commands. Compare the GUI and the CLI and recommend the right interface for each person, justifying with ease of use and resources used.
3. A desktop beeps a pattern after power on and never reaches the desktop. Which boot step is failing, what does the beep code signal, and what should the technician check before the operating system even loads?
4. A parent wonders why a phone with Android behaves so differently from the school desktop running Windows. Compare the mobile and desktop operating systems, and state the four management functions they both perform.
5. Trace exactly what happens from pressing the power button to the desktop appearing, naming all six steps in order and the component involved in the Power-On Self-Test.
6. A single core CPU is asked to run Word, a browser, and a music player at the same time. Using process management and multitasking, explain why all three appear to run simultaneously.
7. A school on a small budget wants a free operating system used on servers and by developers. Recommend which type of operating system from your note to choose, and justify the choice by its developer and licence.