Multiprocessor System

Multiprocessor System

• Multiprocessor system means more than one processor in close communication. All the processor share common bus, clock, memory and peripheral devices.

• Multiprocessor system is also called parallel system or tightly coupled systems. Multiprocessor operating systems are just regular operating systems. They handle system calls, do memory management, provide a file system, and manage I/O devices.

• Multiprocessor systems is also known as parallel systems or multicore systems. 

•Features of Multiprocessor Systems :

1.The processor should support efficient context switching operation.

2. It supports large physical address space and larger virtual address space.

3. If one processor fails, then other processors should retrieve the interrupted process state so that execution of the process can continue.

4.The inter-process communication mechanism should be provided and implemented in hardware as it becomes efficient and easy.

• Multiprocessors can be used in different ways:

1. Uniprossesors (single-instruction, single-data or SISD)

2. Within a single system to execute multiple, independent sequences of instructions in multiple contexts (multiple-instruction, multiple-data or MIMD); 3. 3.A single sequence of instructions in multiple contexts (single-instruction, multiple-data or SIMD, often used in vector processing);

4. Multiple sequences of instructions in a single context (multiple-instruction, single-data or MISD, used for redundancy in fail-safe systems and sometimes applied to describe pipelined processors or hyper threading).

Advantages and Disadvantages of Multiprocessor Systems

 Advantages of Multiprocessor Systems:

1. Throughput : Throughput increases because number of processor is increases.  

2. Cost:Multiprocessor system is cheaper than the multiple single processor Ang system.

3. Reliability: If one processor fails, it has no effect on whole system operation.

4. Response time : Response time is less because of increased number of

processor.

• Disadvantages of Multiprocessor Systems :

1. Multiprocessor systems are more complex in both hardware and software.

2. Additional CPU cycles are required to manage the cooperation, so per-CPU efficiency goes down.

• Multiprocessor systems are of two types: Symmetric multiprocessing and asymmetric multiprocessing.

Symmetric Multiprocessing

• The simplest multiprocessors are based on a single bus. In symmetric multiprocessing, number of homogeneous processor are running independently without affecting other programs.

• Systems that treat all CPUs equally are called symmetric multiprocessing (SMP) systems.

• Each processor uses 'different data and program but sharing some common resources like memory, I/O device etc. Fig. 1.4.1 shows multiprogramming system.

• In SMP, all processor are at the same level. They work in peers. There is no master-slave relationship in between the processor. Each processor shares a single copy of operating system.

• Symmetric multiprocessing is easier to implement in operating systems. Examples of symmetric multiprocessing operating systems are Windows NT 4.0, Novell Netware 2.1 etc.

Asymmetric Multiprocessor

• If all CPUs are not equal, system resources may be divided in a number of ways, including asymmetric multiprocessing (ASMP), non-uniform memory access

(NUMA) multiprocessing, and clustered multiprocessing.

• All CPUs are not equal. There is one master processor and remaining is the slave processor. Each processor has its own memory address space.

• A master processor controls the whole operations. It gives the instruction to the slave processor or slave processor uses some predefined set of tasks.

• Asymmetric multiprocessing has one master CPU and the remainder CPUs are slaves. The Master distributes takes among the slaves and I/O is usually done by the master only.

• Each processor has own task which assign by master processor. Asymmetric multiprocessing is difficult to implement.

Difference between Symmetric and Asymmetric Multiprocessor