Types Of Multiprocessor Operating System

TYPES OF MULTIPROCESSOR OPERATING SYSTEMS
The multiprocessor operating systems are complex in comparison to multiprograms on an uniprocessor operating system because multiprocessor executes tasks concurrently. Therefore, it must be able to support the concurrent execution of multiple tasks to increase processors performance. Depending upon the control structure and its organisation the three basic types of multiprocessor operating system are:
1) Separate supervisor
2) Master-slave
3) Symmetric Supervision

Separate Supervisors
In separate supervisor system each process behaves independently. Each system has its own operating system which manages local input/output devices, file system and memory well as keeps its own copy of kernel, supervisor and data structures, whereas some common data structures also exist for communication between processors. The access protection is maintained, between processor, by using some synchronization mechanism like semaphores. Such architecture will face the following problems:
1) Little coupling among processors.
2) Parallel execution of single task.
3) During process failure it degrades.
4) Inefficient configuration as the problem of replication arises between supervisor/kernel/data structure code and each processor.

Master-Slave: In master-slave, out of many processors one processor behaves as a master whereas others behave as slaves. The master processor is dedicated to executing the operating system. It works as scheduler and controller over slave processors. It schedules the work and also controls the activity of the slaves. Therefore, usually data structures are stored in its private memory. Slave processors are often identified and work only as a schedulable pool of resources, in other words, the slave processors execute application programmes.

This arrangement allows the parallel execution of a single task by allocating several subtasks to multiple processors concurrently. Since the operating system is executed by only master processors this system is relatively simple to develop and efficient to use. Limited scalability is the main limitation of this system, because the master processor become a bottleneck and will consequently fail to fully utilise slave processors.

Symmetric: In symmetric organisation all processors configuration are identical. All processors are autonomous and are treated equally. To make all the processors functionally identical, all the resources are pooled and are available to them. This operating system is also symmetric as any processor may execute it. In other words there is one copy of kernel that can be executed by all processors concurrently. To that end, the whole process is needed to be controlled for proper interlocks for accessing scarce data structure and pooled resources.
The simplest way to achieve this is to treat the entire operating system as a critical section and allow only one processor to execute the operating system at one time. This method is called ‘floating master’ method because in spite of the presence of many processors only one operating system exists. The processor that executes the operating system has a special role and acts as a master. As the operating system is not bound to any specific processor, therefore, it floats from one processor to another.

Parallel execution of different applications is achieved by maintaining a queue of ready processors in shared memory. Processor allocation is then reduced to assigning the first ready process to first available processor until either all processors are busy or the queue is emptied. Therefore, each idled processor fetches the next work item from the queue.