Evolution Of Operating System part2!!!!!

4. Personal Computer System

As hardware costs have increased, it has become feasible to have a computer system dedicated to a single user.

These types of computer systems are usually referred as a personal computer system. The I/O has changed with panels of switches and card readers replaced with typewriters like keyboard and mouse.

Line printer and cardpunches have to display screens and to small fast printer.

Personal computers appear in 1970s. They are microcomputers that considerably smaller and less expensive than the other systems.

PCs operating system therefore were neither multi user nor multi tasking. However the goal of these OS have changed with time instead of maximizing CPU and peripherals utilization

 

5.Parallel Systems

Most systems to date are single-processor systems  i.e. they have only one main CPU. However there is a trends towards multi processor systems.

Such systems have more than one processor in close communication, sharing the computer bus, the clock and sometime memory and peripherals devices.

These system are referred to as a tightly coupled systems. There are several reasons for building such systems.

Advantages

1. Increased throughput by increasing the number of processors we get more work done in a shorter period of time.
2. Less cost multiprocessor systems can also save money
1. To multiple single systems, because the processor share peripherals and power supplies.
2. In several programs are to operate on the same set of data, it is cheaper to store those data in one disk and to have all processors share them, rather than to have many computer with local disk and many copies of data.
3. Increased reliability a functions can be distributed properly among several processors, than the failure of one processor will not halt the system, but rather will only slow it down.

     If we have 10 Processor  and  1 Processor fails Then the rest of the 9 processor must pick up the share of the work of the failed processor.Thus the entire system runs only 10% slower rather than failed together.

Systems that are designed for graceful degradation are also called fault tolerant system.

Types of Multiprocessor System

1.  Symmetric Multiprocessor System

In which each processor runs and identical copy of Os and these copies communicate with each other as needed.

2.  Asymmetric Multiprocessor System

In which each processor assigned a specific task.

A master processor controls the system and the other processors either look to the master for instruction or have predefined task.

This scheme defines a master slave relationship. The master processor schedules and allocates work to the slave processor.

6. Distributed Systems

A recent trend in computer systems is to distribute computation among several processors. In this type of systems, the processors do not share memory or a clock instead each has its own local memory.

The processors communicate with each other through various communication lines, such as high-speed buses or telephone lines.

These systems are usually referred to as a loosely couples systems or distributed system.

Advantages

 1.  Resource sharing (remote access)

If a number of different sites are connected to one another, that a user at one site may be able to use resources of another sites.

2.  Computation speed up

If a particular computation can be partitioned into a number of sub-computations that can run concurrently, then distributed system may allow us to distribute the computation among various sites, to run that computation concurrently.

3. Reliability

If one site fails in a distributed system, the remaining site can potentially continue operating.

   

4.Communication

There are many instances in which programs needs to exchange data with one other. When many sites connected to one another by a communication network, the processes at different site have the opportunity to exchange information.

                              Users may initiate file transfer or communicate with one another via e-mail. A user can send mail to another user at the same site or at a different site.

8.Real Time System

Another form of a special purpose OS is the real time system.

A real time OS has well defined , fixed time constraints. Processing must be done within the defined constraints, or the system will fail.

                                                            A time sharing system, where it is desirable to respond quickly, or to a batch system, where there may be no time constraints at all.

Real time system is used when they’re all rigid time requirements on the operation of a process or the flow of data and is often used as a control device in dedicated application. Sensor brought data and possibly adjusts the controls to modify the sensor input.

Examples:

Scientific experiments, Medical Imaging System, Industrial Control System , Space Experiments.