There are two types of an operating system:
- Single User.
- Multi User.
Single User Operating System
This operating system can run only one program at a time and hence called single user or single task systems. These systems run on microcomputers Only one user is normally in command of the system at any given time. Examples of such type of operating system are DOS-Disk Operating System and Macintosh systems.
- MS-DOS and PC-DOS: When IBM-PC came in the market a new operating system was needed. Then Microsoft Corporation came up with PC-DOS (Personal Computer Disk Operating System) for the IBM-PC. Later the same company developed MS-DOS (Microsoft Disk Operating System) a portable version of PC-DOS, that can run on 8086 family microprocessor. MS-DOS is a command driven system.
As new microprocessors are developed accordingly operating systems are modified and updated. 6.22 is the latest version of MS-DOS available, but most of the computers are running under, windows 95, 97 and 98.
- Macintosh: Apple Macintosh users, uses menus and icons rather than commands. Icons are small symbols that represent commands. Using mouse input device, the user moves a pointer to a word or icon and enters the selection. This system is slower than command driven system.
Multi User Operating System
Since large computers such as mainframes. can perform more functions than microcomputers and are more complex, therefore, operating system requires for such a system must be able to run several jobs at one time. Such operating systems are called multi-user operating systems. These operating systems can run two or More computer programs concurrently. Now-a-days multi-user operating systems have been adopted for microcomputers as well. Examples are multi user operation system.
- UNIX: This operating system is written in C Language, which is a high level language. It is less hardware dependent than the operating system written in low level language. Thus UNIX can easily transport from one system to another. System is surrounded by the shell, which serves as a programming language and as a command language interpreter, reading the user commands and interpreting them as requests to execute certain programs. Around the shell are the utilities such as text processing.
- ZENIX: is an implementation of UNIX operating system for microcomputers. This type of operating system is gained capital rapid acceptance, because of its multiprogramming capabilities and many useful utilities.