Time Sharing System and its Requirements

Time sharing system

· Time sharing refers to the allocation of computer resources in a time dependent fashion to several program simultaneously

· A time sharing system has many user terminals that are connected to same computer simultaneously. Using these terminal, different users can work on a system at the same time

· Thus, it uses multi programming with a special CPU scheduling among all the last one, and then again beginning from the first one

· In time sharing system, the CPU time is divided among all the users on schedule basis.

· It release the CPU under any of the following three conditions:

1. When the allotted time slice expires.

2. When the program needs to perform I/O operation.

3. When the execution of the program is over during the time slice

· Thus the time sharing, when the CPU is allocated to user program, the user uses the CPU for the period of time slot.

single user operating system

2. Multi user operating system

3. Batch processing operating system

4. Multi programming operating system

5. Multi tasking operating system

6. Multiprocessing operating system

7. Time sharing operating system

8. Real time system

Time sharing system

· In time sharing system the various program can be in one of the following three stses

1. Running: the users program currently has control of the CPU, only one user will be active at a time.

2. Ready : the user program is ready to execute but is waiting for its turn to get the CPU. More than one user can be in ready state at a time.

3. Blocked : the user’s program is waiting for some I/O operation. More than one user can be wait state at a time.

· Requirement of time sharing system

Time sharing system typically the following additional hardware and software features:

1. A number of terminals simultaneously connected to the system, so that multiple users can simultaneously use the system in interactive mode.

2. A relatively large memory to support multi programming.

3. Memory protection mechanism to prevent mechanism to prevent one jobs complete status information when the CPU is taken away from it, and restoring this information back, before the CPU is given back to it again.

4. An alarm clock mechanism to send an interrupt signal to the CPU after every time slice.3.

5. A special CPU scheduling algorithm, which allocates the CPU for a very short periods, to each user process in a circular fashain.

Advantage and Disadvantage of time sharing system

1. Reduces CPU idle time . time sharing reduce idle time of CPU and increase the utilization of CPU by switching from one program to another in rapid succession.

2. Provides advantages of quick response time. The special CPU scheduling algorithm used in time sharing system ensure quick response time to all users.

Distributed system

· A distributed system is a collection of processor located in geographical dispersal physical location.

· In this system, the workhold is distributed or divided between two or more computers that are linked together by communication network . that is the different processors communicate using communication links, such as telephone lines and buses3

· The various processors do not share memory, clock ,or peripheral devices instead each processors has its local memory.

· The purpose of distributed system is to provide an efficient and convenient environment for sharing of resources.

· Some example of distributed operating system are amoeba, angle, chorus, much, alpha kernel.

· The processors in a distributed system vary in size and function. They may include small microprocessors, workstations microcomputers, mainframe computers and large general purpose computers.

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