Software & Operating Systems
🔒 Log in to trackOperating system functions, types and booting
🔒 Log in to trackThe operating system (OS) is system software. It manages the hardware and gives programs a place to run. It handles processes, memory, files, devices, security and the user screen. The kernel is its core. Booting is the start-up of the OS.
What an operating system is
The operating system (OS) manages all hardware and software. It gives applications a platform to run on. It is the first big program loaded, and it stays in memory until shutdown. Without an OS, the machine is only electronics.
The services an OS provides
| Service | What it does |
|---|---|
| Process management | Decides which waiting program gets the CPU next (scheduling) |
| Memory management | Gives RAM to programs and takes it back. Virtual memory uses the disk as extra RAM |
| File management | Folders, names, saving and finding files through the file system |
| Device management | Talks to hardware through drivers |
| Security | Usernames, passwords and permissions |
| User interface | The screen you work on: GUI (Windows) or command line (DOS) |
The OS also handles errors, networking and resource allocation.
Tip: The six main services spell PMF-SUIE: Process, Memory, File, Security, User interface, Error handling.
Types of operating systems
| Type | Idea | Where you meet it |
|---|---|---|
| Single-user, single-task | One user, one program at a time | Old MS-DOS |
| Single-user, multitasking | One user, many programs at once | Windows on a PC |
| Multi-user | Many users share one machine | UNIX/Linux servers |
| Multiprogramming | Several programs sit in RAM. The CPU switches when one waits for input or output | Server systems |
| Time-sharing | CPU time is cut into small slices shared among users | Mainframes |
| Real-time (RTOS) | Must answer within a fixed deadline | Missiles, robots, medical devices |
| Distributed | Many networked machines act as one | Data centres |
| Embedded | A small OS built into a device | Washing machine, router |
| Mobile | Made for smartphones | Android, iOS |
Rule: In a real-time system, a late answer counts as a failure.
Kernel and shell
- Kernel: the core of the OS. It always stays in memory. It does scheduling, memory work and device work.
- Shell: the outer layer. It takes your commands and passes them to the kernel. It can be a CLI (typed commands) or a GUI (desktop).
Picture the kernel as the engine and the shell as the steering wheel.
Booting
Booting means starting the OS.
- Cold boot: power on from the off state.
- Warm boot: restart without cutting power.
The steps run in a fixed order.
- Power on. The CPU jumps to the BIOS/UEFI firmware.
- POST (Power-On Self-Test) checks the hardware.
- BIOS/UEFI finds the boot device.
- The boot loader loads the kernel into RAM.
- The OS takes charge and the login screen appears.
Watch: POST always comes first. The order is POST, boot loader, kernel, login.
Question types you will see
Each type: how to recognise it, the method step by step, and one question to try.
OS service identification
A job is described (giving RAM, choosing the next CPU task, managing folders, usernames) and the OS function is asked.
Find the object of the job: RAM, CPU, files, devices or users.
Match it to its service in the table.
Pick that service.
Each OS service handles exactly one kind of resource.
Giving RAM to each running program is the function of
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The resource is RAM.
The service that handles RAM is memory management.
Memory management
OS type from the situation
A scenario is given (missile guidance, many users on one server, a washing machine) and the OS type is asked.
Find the key word: deadline, many users, time slices, small device.
Match it to the type table.
Pick the matching type.
Every OS type has one signature situation.
An OS that must respond within a fixed deadline, as in missile guidance, is a
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A fixed deadline is the key word.
Late answers count as failure.
Real-time operating system (RTOS)
Kernel, shell and interface
The core of the OS, the part that takes commands, or CLI versus GUI is asked.
Core that stays in memory means kernel.
Part that takes your commands means shell.
Typed commands mean CLI. Icons and windows mean GUI.
The kernel does the work. The shell only takes commands and passes them on.
The part of the OS that accepts your commands and passes them to the core is the
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The core is the kernel.
The layer that accepts commands is the shell.
Shell
Boot sequence, POST, cold and warm boot
The first check at start-up, the order of boot steps, or restart without power-off is asked.
Recall the order: POST, boot loader, kernel, login.
Cold boot means from off.
Warm boot means restart without a power cut.
The boot order is fixed, so it can be learned as one chain.
Arrange in order: A. Boot loader B. POST C. Kernel loads D. Login screen
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POST runs first.
The boot loader comes next.
It loads the kernel.
The login screen appears last.
B, A, C, D
Multiprogramming, time-sharing and multitasking
The question describes how the CPU is shared and asks for the name.
Check what is shared: RAM slots or CPU time.
CPU switches when one program waits for I/O: multiprogramming.
CPU time cut into slices among users: time-sharing.
The trigger for the switch decides the name.
An OS gives each user a small slice of CPU time in turn. This is called
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Slices of CPU time are the key idea.
That is time-sharing.
Time-sharing
Mobile operating systems
A question asks which OS a phone uses, or which kernel Android is built on.
Recall Android is Linux-kernel based.
Recall iOS belongs to Apple.
Pick the option that fits.
Only two mobile names are usually asked.
Android is based on which kernel?
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Android is a mobile OS.
It is built on Linux.
The Linux kernel
Shortcuts that save time
The OS gives Process, Memory, File, Security, User interface and Error handling. A 'manage the machine' answer is OS work. Computing payroll is application work.
Which OS service gives RAM to programs?
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The question is about RAM.
RAM work belongs to memory management.
Memory management
Cold boot starts from a cold, switched-off machine. Warm boot restarts without a power cut. POST always comes first.
Restarting a running computer is called
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Power stays on.
That is a warm boot.
Warm boot
Mistakes to avoid
Where most students lose marks on this subtopic.
Mixing up multiprogramming and time-sharing.
Multiprogramming keeps many programs in RAM. Time-sharing gives each user a slice of CPU time.
Saying the shell stays in memory as the OS core.
The kernel is the core that stays in memory. The shell is the interface.
Putting the boot loader before POST.
The order is POST, boot loader, kernel, login.
Calling a restart a cold boot.
A cold boot starts from power off. A restart is a warm boot.
Thinking iOS runs on many brands of phone.
iOS is Apple's mobile OS. Android runs on the Linux kernel.
Quick revision
Read this the night before the exam.
Main services: process, memory, file, device, security, user interface.
Virtual memory uses the disk as extra RAM.
Multiprogramming = many programs in RAM. Time-sharing = CPU time slices. RTOS = fixed deadline.
Kernel = core, always in memory. Shell = interface (CLI or GUI).
Boot order: POST, boot loader, kernel, login.
Cold boot = from off. Warm boot = restart without power cut.
Android is based on the Linux kernel.
Practice: 19 questions
Sets of 10, mixed across the question types above. Every answer has a step-by-step explanation.
Topic test · 10 questions
Suggested time 5 min · wrong answers go to your mistake notebook automatically.