Multiprocessing Operating System

Multiprocessor Operating system is the system that contains two or more processors or CPUS and has ability to simultaneously execute several programs. Hence the name “multi- processor”.
In such a system, multiple processors share the clock, bus, memory and peripheral devices.
A multiprocessor system is also known as parallel system.
In such a system, instructions from different and independent programs can be processed at the same instant of time by different CPUS.
In this system, the CPUS may simultaneously execute different instructions from the same program.

Multiprocessor systems are categorized into two different types:

Symmetric multiprocessing (SMP)
Asymmetric multiprocessing (ASMP)

1. Symmetric multiprocessing (SMP)

In SMP, each processor runs an identical copy of the operating system.
The processors can communicate with each other and execute these copies concurrently.
In this, all the processors are identical and perform same function. As a result they share equal amount of load.
Therefore, SMP exhibit peer-to-peer relationship.

For example, Encore’s version of UNIX for the multi-max computer uses SMP. In this system, various processors execute copies of Unix operating system thereby executing m processes if there are m processors.

2. Asymmetric Multiprocessing (ASMP)

In ASMP, different processor do different things i.e., they are not identical. Thus, there is imbalance among the processors. Hence the name ‘asymmetric.
In ASMP each processor is given a specific task and do not share equal load.
There is master-slave relationship between the processors.
One of the processors that controls the system is called master. The other processors follow the instruction given by the master or have predefined tasks. These are called slaves.
Thus, in ASMP, the master processor controls, schedules and allocates the task to the slave processors.

For example, calculations is based on asymmetric multiprocessing system. Processor operated with math co-processor used to handle floating-point.

Advantages of Multiprocessing System

1. Improved Reliability

Multiprocessing systems have better reliability than sine processor because of the presence of multiple processors. If one of the processors break down, the other processor(s) automatically takes over the system workload repairs are made. Hence, a complete breakdown of such system can be avoided.

2. Improved throughout

Throughout is the number of jobs executed per unit time a user submits his job to the system for processing of segments of programs is possible. Consequently the throughout and performance of system is improved.

3. Lowered Turnaround time

Turnaround time is the difference between the time a user submits his job to the system for processing and the time he receives results. When a job is divided among the multiple processors the computation of result takes less time As a result turnaround time is less.

4. Efficient Utilization of all resources

In addition to the processors, it also facilitates more efficient utilization of all the other devices of the computer system 5. Economical. The clock, bus, peripheral devices and memory are shared. As a result, it is cheaper to have multiprocessor systems than multiple single processor systems.

Disadvantages of multiprocessing system

A very sophisticated operating system is required to schedule balance and coordinate the input, output and processing activities of multiple CPUS.
A large man memory is required for accommodating the sophisticated operating system along with several user programs
Such systems are very expensive. In addition to the high charges paid initially. the regular operation and maintenance of these systems is also a costly affair