Operating System is the most fundamental program that runs on a computer, which keeps all components of a computer such as keyboard, display screen, memory, hard disk, CPU and application software working together. It also controls peripheral devices such as disk drives and printers. The other key function of the operating system is to provide a software platform on top of which other application programs can run without knowing the details of the hardware.
For large and distributed systems, the operating system also controls different programs and users running simultaneously. The operating system is also responsible for security of computers and networks in various ways.
Operating systems have the following categories:
- Single-user, single task - this type of operating system is designed to manage the computer so that one user can effectively do one thing at a time. The Palm OS is an example of this type of operating system.
- multi-user: Allows two or more users to run programs at the same time. Unix, VMS and mainframe operating systems, such as MVS, are examples of multi-user operating systems.
- Single user, multitasking: Allows more than one program to run concurrently. Microsoft's Windows and Apple's Mac OS platforms are both examples of this type of OS.
- real time: Responds to input instantly. Real-time operating systems are used to control machinery, scientific instruments and industrial systems. General-purpose operating systems, such as DOS and UNIX, are not real-time.
- multiprocessing: Supports running a program on more than one CPU.
- multithreading: Allows different parts of a single program to run concurrently.
User normally interacts with the operating system through GUI such as Windows graphic user interface or a set of commands such as DOS. The application programs must be written to run on top of a particular operating system. The most popular current Operating Systems are:
- Windows: The Microsoft OS installed on 90% of PCs
- UNIX: Originally developed by AT&T Bell Labs for servers
- Linux: A shareware OS with increasing popularity on servers and desktops
- Mac OS: The Apple Computer OS for its personal computers
- OS/2: An IBM operating system for PC which is exiting the market