Software types
| Type | Purpose | Examples |
|---|---|---|
| System software | Runs and manages the hardware | Operating systems, device drivers, firmware |
| Utility software | Maintains and protects the system | Antivirus, disk cleanup, defragmenter, file compression (ZIP), backup |
| Application software | Helps the user do a task | MS Word, Excel, Tally, web browsers, banking apps |
| Programming software | Helps write programs | Compilers, interpreters, assemblers, IDEs |
A device driver lets the OS communicate with a specific hardware device, such as a printer or graphics card.
Operating system
The OS is system software that acts as an interface between the user and the hardware and manages all resources. Its core is the kernel, which stays in memory and controls the CPU, memory and devices. The shell is the interface (command line or GUI) through which users talk to the kernel.
Functions of an OS
- Process management (CPU scheduling, creating and ending processes)
- Memory management (allocating RAM, virtual memory, paging)
- File management (creating, naming, organising folders)
- Device (I/O) management through drivers
- Security and user accounts; providing a user interface
Types of operating systems
| Type | Key idea |
|---|---|
| Batch | Similar jobs grouped and run without user interaction |
| Multiprogramming | Several programs kept in memory so the single CPU is never idle |
| Multitasking / time-sharing | CPU time divided into slices so many users or tasks seem to run at once |
| Multiprocessing | Two or more CPUs in one computer work simultaneously |
| Real-time (RTOS) | Guaranteed response within strict time limits – air traffic control, robots, pacemakers |
| Distributed | Many networked computers appear as one system |
| Network OS | Manages shared resources on a network (e.g. Windows Server) |
| Mobile OS | Android (Google, Linux kernel), iOS (Apple) |
Popular operating systems
- MS-DOS – command line, single-user, single-tasking. Commands:
DIR(list files),CD(change directory),MD(make directory),DEL(delete),COPY,CLS(clear screen). - Windows – Microsoft GUI OS; current versions Windows 10 and 11; file system NTFS.
- Linux – open-source kernel released by Linus Torvalds in 1991; distributions such as Ubuntu, Fedora; file system ext4.
- Unix – developed at Bell Labs (Ken Thompson, Dennis Ritchie) around 1969.
- macOS / iOS – Apple; file system APFS.
- Android – Google; based on the Linux kernel.
Key OS concepts
| Term | Meaning |
|---|---|
| Process | A program in execution |
| Thread | Smallest unit of execution within a process |
| Deadlock | Processes wait forever for resources held by each other |
| Starvation | A low-priority process waits indefinitely because others keep getting the resource |
| Paging | Memory divided into fixed-size pages and frames |
| Thrashing | Excessive paging; system spends more time swapping than working |
| Spooling | Simultaneous Peripheral Operations On-Line – queues print jobs on disk |
| Fragmentation | Files stored in scattered pieces; fixed by a defragmenter |
CPU scheduling algorithms
- FCFS – First Come First Served (simple queue).
- SJF – Shortest Job First (lowest average waiting time).
- Round Robin – each process gets a fixed time quantum in turn; used in time-sharing.
- Priority – highest priority first; can cause starvation (solved by ageing).
Software licensing
- Freeware – free to use, source code not given.
- Shareware – free trial; pay to continue.
- Open source – source code available to view, modify and share (Linux, LibreOffice, Firefox).
- Proprietary – owned and licensed by a company (Windows, MS Office).
Windows essentials
- Recycle Bin holds files deleted from the hard disk until it is emptied; Shift+Delete skips it.
- Task Manager (Ctrl+Shift+Esc) shows running processes and performance.
- Control Panel / Settings change system settings; Device Manager manages drivers.
- Common extensions:
.exe(program),.txt(plain text),.jpg/.png(images),.mp3(audio),.mp4(video),.zip(compressed),.pdf(portable document).
Exam tip: "More than one CPU" is multiprocessing; "many programs, one CPU" is multiprogramming; "strict deadline" is real-time.