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Operating systems are mainly two types:

Real-time: A real-time operating system a system which is multitasking that is helpful in executing real-time applications. This is often used in specialized scheduling algorithms.
operating system

This type of operating systems is used to control Scientific devices and similar small instruments. These type of devices have very limited or no end-user utilities.

 Types of Operating Systems

The main objective of real-time operating systems is their quick and predictable response to events. They have an event-driven or time-sharing design and often aspects of both. An event-driven system switches between tasks based on their priorities or external events while time-sharing operating systems switch tasks based on clock interrupts.

Examples: VxWorks, QNX, eCos, RTLinux

Multi-user: A multi-user operating system allows multiple users to access a computer system at the same time. This should not be confused with the multi-user accounts in windows  or similar, the main difference is, the network administrator is the only actual user in Windows or Macs and one more difference being that in OS like Unix more than one user can simultaneously login while this is not possible in windows.

Time-sharing systems and Internet servers can be classified as multi-user systems as they enable multiple-user access to a computer through the sharing of time.

Examples: Unix, Linux, Solaris etc..

Multi-tasking vs Single-tasking:

A multi-tasking operating system allows more than one program to be running at a time, from the point of view of human time scales.
A single-tasking system has only one running program.

Multi-tasking is two types: Pre-emptive and Co-operative.

Preemptive multitasking, the operating system slices the CPU time and dedicates one slot to each of the programs. Unix-like operating systems such as Solaris and Linux support pre-emptive multitasking. The act of taking control of the operating system from one task and giving it to another task is called preempting.

Cooperative multitasking is achieved by relying on each process to give time to the other processes in a defined manner. 16-bit versions of Microsoft Windows used cooperative multi-tasking. 32-bit versions of both Windows NT and Win9x, used pre-emptive multi-tasking. Mac OS prior to OS X used to support cooperative multitasking.

Cooperative multitasking requires the programmer to place calls at suitable points in his code to allow his task to be de-scheduled which is not always easy if there is no obvious top-level main loop or some routines run for a long time.

Distributed:

A distributed operating system is a software over a collection of independent, networked, communicating, and physically separate computational nodes. A distributed operating system manages a group of independent computers and makes them appear to be a single computer. Distributed computations are carried out on more than one machine. When computers in a group work in cooperation, they make a distributed system.

Embedded:

Embedded operating systems are designed to be used in embedded computer systems. They are designed to operate on small machines like PDAs with less autonomy. They are able to operate with a limited number of resources. They are very compact and extremely efficient by design.

An embedded system is a computer that is part of a different kind of machine. Examples include computers in cars, traffic lights, digital televisions, ATMs, digital cameras, GPS navigation systems, elevators, digital media receivers and smart meters, among many other possibilities. 

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