Software & Operating Systems
🔒 Log in to trackOperating system functions, types and booting
🔒 Log in to trackAn Operating System is the system software that manages hardware and provides the platform for applications.
Functions: process management (CPU scheduling of tasks), memory management (allocating RAM, virtual memory), file management (folders, FAT32/NTFS), device management (via drivers), security (users, passwords, permissions), user interface (GUI/CLI), error handling, networking and resource allocation. The kernel is the core of the OS that always stays in memory.
Types: single-user single-task (old DOS), single-user multi-task (Windows desktop), multi-user (UNIX/Linux servers), multiprogramming (several programs in RAM; CPU switches when one waits for I/O), multitasking, time-sharing (CPU time slices among users), real-time (RTOS) (guaranteed response within deadlines - missiles, robots, medical devices), distributed (many networked machines acting as one), embedded, mobile (Android - Linux kernel based; iOS; Windows).
Booting = starting the OS. Cold boot = power-on from off; Warm boot = restart without cutting power. Sequence: power-on -> POST (Power-On Self-Test) -> BIOS/UEFI finds the boot device -> boot loader loads the kernel -> login screen.
Detailed notes
What an operating system is
The operating system (OS) is the system software that manages all hardware and software and gives applications a platform to run on. It is the first big program loaded and stays in memory till shutdown. Without an OS, the machine is just electronics.
The six services every OS provides
| Service | What it does |
|---|---|
| Process management | Decides which waiting program gets the CPU next (scheduling) |
| Memory management | Allots RAM to programs; extends it with virtual memory (disk used as extra RAM) |
| File management | Folders, naming, saving, retrieving files through the file system |
| Device management | Talks to hardware through drivers |
| Security | Usernames, passwords, permissions |
| User interface | The screen you work on — GUI (Windows) or command line (DOS) |
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 simultaneously | Unix/Linux servers |
| Multiprogramming | Several programs sit in memory; the CPU switches among them | Server systems |
| Time-sharing | CPU time sliced into small quanta shared round-robin among users/tasks | University mainframes |
| Real-time (RTOS) | Responds within a fixed deadline; late answer = failure | Missile control, pacemakers, industrial robots |
| Distributed | Many networked computers appear as one system | Cloud data centres |
| Embedded | Small OS baked into an appliance | Washing machine, router, smart TV |
| Mobile | For smartphones | Android (Google, Linux kernel), iOS (Apple) |
Kernel and shell
- Kernel — the core of the OS, always in main memory; does scheduling, memory and device work.
- Shell — the outer layer that takes your commands and passes them to the kernel; may be a CLI (typing commands, like MS-DOS) or a GUI (Windows desktop). Picture: kernel = the engine, shell = the steering wheel and dashboard.
Booting — how the machine wakes up
- Power on → CPU jumps to the BIOS/UEFI firmware chip.
- POST (Power-On Self-Test) — hardware quick check (beep if fine).
- BIOS finds the boot device and runs the boot loader.
- Boot loader loads the kernel into RAM; OS takes charge; login screen appears.
- Cold boot — starting from a powered-off state.
- Warm boot — restarting without cutting power (Restart option). Order is fixed: POST → boot loader → kernel → login.
Quick revision
- Six services: process, memory, file, device, security, interface.
- Multiprogramming = many programs in memory, one CPU switching. Time-sharing = time slices. RTOS = deadline.
- Kernel in memory (engine); shell is the interface (CLI or GUI).
- Boot order: POST → boot loader → kernel. Cold = from off; warm = restart.
- Android runs on the Linux kernel; iOS is Apple-only.
Types of questions asked
Every way this subtopic shows up in exams — how to recognise it, the formula or logic to use, and a solved example.
Type 1: OS service identificationvery common3 practice Q
A job is described — allotting RAM, choosing the next CPU task, managing folders, drivers for hardware, usernames — and the OS function is asked.
- Match the job: CPU turn → process management; RAM → memory management; folders/files → file management; drivers → device management; passwords → security; screen → user interface.
- 'Which program gets the CPU next' is the single most asked service — process scheduling.
- Virtual memory (disk acting as extra RAM) belongs to memory management.
Example: Allotting RAM to each running program is the function of —
Memory management — the OS tracks every byte of RAM and allots/frees it for each process, using virtual memory when RAM runs short.
Type 2: OS type from the situationvery common4 practice Q
A scenario is given — missile guidance, many students sharing one server, ATM deadlines, a washing machine's controller — and the OS type is asked.
- Deadline = real-time; many users at once = multi-user/time-sharing; many programs resident = multiprogramming; appliance = embedded; network-as-one = distributed; one user many apps = multitasking.
- RTOS keywords: 'immediately', 'within a fixed time', 'missile', 'industrial control'.
- Embedded = inside a machine, single purpose, no user programs.
Example: An operating system that must respond within a fixed deadline (missile guidance, industrial robots) is a —
Real-time operating system (RTOS) — a late response is as bad as a wrong one; ordinary desktop OSes give no such guarantee.
Type 3: Kernel, shell and interface questionscommon2 practice Q
'The core of the OS that always stays in memory is', 'the part that takes user commands is', CLI vs GUI identification.
- Kernel = in-memory core (scheduling, memory, devices). Shell = the interface layer (CLI or GUI) between user and kernel.
- CLI = typed commands (MS-DOS, Linux terminal); GUI = windows, icons, menus, pointer (Windows).
- Trap: calling the desktop/shell the kernel.
Example: The part of the operating system that accepts your commands and passes them to the core is the —
Shell — the interface layer (command line or GUI desktop). The kernel is the in-memory core that actually executes the work.
Type 4: Booting sequence, POST, cold vs warmcommon4 practice Q
'What is the first check when the computer starts?', 'restart without power off is called', 'correct order of boot steps'.
- Order: POST (Power-On Self-Test) → boot loader → kernel loads → login.
- Cold boot = power was off; warm boot = restart without cutting power.
- POST always precedes the boot loader — reversing them is the standard trap.
Example: Put in order: A. Boot loader B. POST C. Kernel loads D. Login screen
B, A, C, D — BIOS runs POST first, then hands to the boot loader, which loads the kernel, and finally the login screen appears.
Shortcut tricks
⚡ PMF-SUIE services
OS gives six services: Process, Memory, File, Security, UI, Error handling. 'Manage + platform' answers are OS; anything computing payroll is application.
Example: Which OS service allocates RAM to programs?
Memory management.
⚡ Boot words
Cold boot = Current was off (switched on from cold); Warm boot = Without power cut (restart). POST always comes first: 'Power On, Self-Test, then load'.
Example: Restarting a running computer is?
Warm booting.
Where students lose marks
Calling the shell/GUI the kernel - the kernel is the in-memory core; the shell is its outer interface.
Saying multiprogramming means several CPUs - it is one CPU juggling several resident programs.
Ordering the boot loader before POST - POST always runs first.
Practice sets — 19 questions
Sets of 10, mixed across the question types above. Each answer comes with a step-by-step explanation.
Topic test · 10 questions
Suggested time 5 min · wrong answers go to your mistake notebook automatically.