Operating Systems: Functions, Types and Concepts
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Key points
- The kernel is the core of the OS; the shell is the user interface to it
- CLI needs typed commands; GUI uses icons and a mouse
- RTOS guarantees a response within a fixed time
- Multiprogramming keeps the CPU busy; multitasking runs several user applications
- Virtual memory uses disk space as an extension of RAM
- Linux is open source, first developed by Linus Torvalds in 1991
- Android runs on the Linux kernel; BOSS Linux is from C-DAC
- Win+L locks the machine; Shift+Delete deletes permanently
On this page
What an operating system does
An operating system is system software that acts as the interface between the user and the hardware. Its main functions are process management, memory management, file management, device management, security and providing a user interface.
Kernel and shell
- Kernel: the core of the OS, which directly controls the hardware.
- Shell: the interface that passes user commands to the kernel.
Key point
The kernel is the core and the shell is only the outer interface. Interchanging the two is one of the most common errors in this topic. BIOS is firmware, not an operating system.
User interfaces
- CLI, Command Line Interface: commands are typed, as in MS-DOS or a Linux terminal.
- GUI, Graphical User Interface: icons, menus and a mouse, as in Windows.
Types of operating system
| Type | Feature |
|---|---|
| Batch | Similar jobs grouped and processed together |
| Time-sharing | CPU time divided among many users |
| Real-time (RTOS) | Guaranteed response within a fixed time, as in air traffic control |
| Distributed | Many computers behave as one system |
| Network | File and printer sharing through a server |
| Mobile | Android and iOS |
Multitasking concepts
- Multiprogramming: several programs in memory so the CPU is never idle.
- Multitasking: one user running several applications at once.
- Multiprocessing: more than one CPU in use.
- Multithreading: several threads inside a single process.
Virtual memory and other terms
Virtual memory uses part of the disk as an extension of RAM. In Windows this is the page file and in Linux it is swap space. Paging divides memory into equal-sized pages, and thrashing is the slowdown caused by excessive paging.
- Spooling: queuing print jobs and sending them one at a time.
- Deadlock: two processes waiting forever for resources held by each other.
- CPU scheduling: FCFS, SJF, Round Robin using a time quantum, and Priority.
Major operating systems
Windows is from Microsoft and is proprietary. macOS is from Apple. Unix came from Bell Labs. Linux is an open-source kernel first developed by Linus Torvalds in 1991, with distributions such as Ubuntu and Fedora. Android is from Google and is built on the Linux kernel. BOSS, Bharat Operating System Solutions, is an Indian Linux distribution developed by C-DAC.
Windows shortcuts
| Shortcut | Action |
|---|---|
| Win+L | Lock the computer |
| Win+D | Show or hide the desktop |
| Win+E | Open File Explorer |
| Win+R | Run dialog |
| Ctrl+Shift+Esc | Open Task Manager directly |
| Ctrl+Alt+Del | Security options screen |
| Shift+Delete | Delete permanently, bypassing the Recycle Bin |
| Alt+Tab | Switch between open windows |
Exam tip
Ctrl+Shift+Esc opens Task Manager directly, while Ctrl+Alt+Del first shows an options screen. This near-pair is asked very often.
Practice questions
Answer all, then check. Explanations appear after checking.
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