Types of OS | based on capability of Processing | Principles of OS

Operating systems are classified into different types depending on their capability of processing:

• Single-user
• Single-tasking
• Multi-user
• Multi-tasking (Multiprogramming)
• Multi-threaded

Generally operating systems (OS) fall into below categories:

• Single-user, Single Tasking systems (Example: MS-DOS)
• Single-user, Multi-tasking systems (Example: Windows, Apple’s Macintosh, OS/2)
• Multi-user, Multi-tasking systems (UNIX, LINUX)

Single-user OS

Operating system supports only one user at a time. This means only one person can use a computer system. Examples of Single-user operating systems are:

• MS-DOS
• Windows XP
• Windows Vista
• Windows 7
• Mac OS

Note:

Being able to use MULTIPLE ACCOUNTS on windows OS doesn’t make it a multi-user system. Only one user out of multiple accounts can use the computer system.

Single-tasking OS

• Only one task can be done at a time
• Task is also known as job or program or process
• Task can be typing a letter, printing a document, listening to a song, scanning a photo, downloading a file from Internet etc.
• MS-DOS is example of Single-tasking operating system

Multi-tasking (Multiprogramming)

Early computer systems allowed only one program to be executed at a time. This program has complete control of the system and had access to all the system’s resources. Current day computer systems allow multiple programs to be executed simultaneously. The notion of a process resulted to execute many programs simultaneously.

Single user systems such as windows able to run several programs (WORD, VLC player, BROWSER, EMAIL etc.) at a time.

• Task is a job to be done. Examples of task may be type a letter, printing a document, listening to a song, scanning a photo, downloading a file etc.
• Allows execution of more than one task at a time. For example, user can listen to music while typing a letter in MS-Word
• More than one program can be run at a time

Multi-user OS

• More than one user can use the computer (machine) at a time
• Allows more than one user to share the same computer at the same time
• Supported via terminals (Network connection)
• Note that a multi-user system is also a multi-tasking system
• Time sharing systems & Internet servers can be classified as multi-user systems as they enable multiple users to access a computer through the sharing of time

Multi-user OS allows a number of users to use the same system (PC) at a time. Example is UNIX/LINUX. Multi-user OS is one that can serve the needs of many users at the same time. The OS divides the total CPU time into number of slices and executes the tasks one after another in a given priority. The switching is done so fast that the user has illusion that total computer is available to him or her.

Multi-user system is also known as time sharing system. In time sharing system, the CPU time is divided among all the users on a scheduled basis.

For example, the 1 sec may be divided into 50 time slices of 20 msec. Each task is executed for 20 msec and its state is saved and another started.