Types of Operating System

1. Single User OS
–Single-user operating systems have no facilities to distinguish users, but may allow multiple programs to run in tandem
2. Single Tasking OS
–A single-tasking system can only run one program at a time
•Features of Single User and Single Tasking OS
–MS-DOS and Palm OS
–Take up little space on disk
–Run on inexpensive computer

3. Multi Taskin (Time Sharing) OS
   Multiprocessing and Multitasking are used interchangeable BUT
–multiprocessing sometimes implies that more than one CPU is involved.
–The ability to execute more than one task at the same time is called as multitasking.

Multi-tasking operating system allows more than one program to be running in concurrency.


In multitasking, only one CPU is involved, but it switches from one program to another so quickly that it gives the appearance of executing all of the programs at the same time.

This is achieved by time-sharing, dividing the available processor time between multiple processes that are each interrupted repeatedly in time slices.

Examples: Linux, Scolaris, Windows NT, AmigaOS





4. Multi User OS
A multi-user operating system extends the basic concept of multi-tasking with facilities that identify processes and resources belonging to multiple users, and the system permits multiple users to interact with the system at the same time.

Gives illusion that each user has his own machine.

Each user has a unique session.

5. Distributed System



A distributed operating system manages a group of distinct computers and makes them appear to be a single computer.

A distributed computer system is a collection of autonomous computer systems capable of communication and cooperation via their hardware and software interconnections.

Advantages of distributed System
Resources Sharing
Computation speed up
 load balancing
Scalability
Reliability
Fail-Safe

6. Real time systems
Real time systems are used in time critical environments where data must be processed extremely quickly because the output influences immediate decisions.

Real time systems are used for space flights, airport traffic control, scientific experiments industrial processes, sophisticated medical equipments, telephone switching etc

Each process is assigned a certain level of priority that corresponds to the relative importance of the event that it services.

The processor is normally allocated to the highest-priority process among those that are ready to execute.

7. Embedded Systems
OS embed on the System itself
Fast, Application specific
Examples Processor in modern washing machines, Cell phones, Control systems etc…