Multiprocessor Systems

Multiprocessor Systems

· Multiprocessor systems (also known as parallel systems or tightly coupled systems) have more than one processor in close communication,sharing the computer bus, the clock, and sometimes memory and peripheral devices.

· Multiprocessor systems have three main advantages.

o Increased throughput. o The economy of scale.

o Increased reliability.

· If functions can be distributed properly among several processors, then the failure of one processor will not halt the system, only slow it down. If we have ten processors and one fails, then each of the remaining nine processors must pick up a share of the work of the failed processor. Thus, the entire system runs only 10 percent slower, rather than failing altogether. This ability to continue providing service proportional to the level of surviving hardware is called graceful degradation. Systems designed for graceful degradation are also called fault tolerant.

· Continued operation in the presence of failures requires a mechanism to allow the failure to be detected, diagnosed, and, if possible, corrected.

· The most common multiple-processor systems now use a symmetric multiprocessing (SMP), in which each processor runs an identical copy of the operating system, and these copies communicate with one another as needed.

· Some systems use asymmetric multiprocessing, in which each processor is assigned a specific task. A master processor controls the system; the other processors either look to the master for instruction or have predefined tasks. This scheme defines a master-slave relationship. The master processor schedules and allocates work to the slave processors.