Operating System
The Operating System (OS) is the main system software. It is the interface between the user and the hardware and manages all resources.
Functions
- Process management: decides which program gets the CPU and when.
- Memory management: allots and frees RAM.
- File management: creates, stores, names and protects files.
- Device management: controls input and output devices through drivers.
- Security: passwords, user accounts, permissions.
- User interface: GUI (icons, windows) or CLI (typed commands).
Types of operating systems
| Type | Meaning | Example |
|---|---|---|
| Batch | Jobs collected and run in groups without user contact. | Early payroll systems |
| Multiprogramming | Several programs in memory; CPU switches when one waits for input or output. | |
| Time-sharing | CPU time shared in small slices among many users. | Unix |
| Multitasking | One user runs many tasks together. | Windows |
| Multiprocessing | Two or more CPUs work together. | |
| Real-time (RTOS) | Must respond within a fixed time. Hard (missile, pacemaker) and soft (video streaming). | |
| Distributed | Many computers act as one system. | |
| Network OS | Manages a network. | Windows Server |
| Mobile OS | For phones and tablets. | Android, iOS |
| Embedded | Inside devices. | Washing machine, ATM |
Kernel and shell
- Kernel: the core of the OS, in direct contact with the hardware. Linux is a kernel.
- Shell: the program that takes your commands and passes them to the kernel. Bash is a popular shell.
Booting
Booting is starting the computer and loading the OS into RAM. Steps: power on → POST (Power-On Self Test) → BIOS/UEFI finds the bootloader → OS loads. Cold boot = starting from power off. Warm boot = restart without turning power off (Ctrl + Alt + Delete or Restart).
Keep practising
Notes are only half the work. Test yourself with questions and discuss doubts with other aspirants.
Prepared for exam revision from standard computer textbooks, Microsoft documentation and official sources. Features differ between Excel and Word versions (2016, 2019, 2021, 365) so check which version your exam follows. Found a mistake? Tell us.