Symmetric and Asymmetric Multiprocessing

The difference between symmetric and asymmetric multiprocessing:

Asymmetric multiprocessing - In asymmetric multiprocessing (ASMP), the operating system typically sets aside one or more processors for its exclusive use. The remainder of the processors run user applications. As a result, the single processor running the operating system can fall behind the processors running user applications. This forces the applications to wait while the operating system catches up, which reduces the overall throughput of the system. In the ASMP model, if the processor that fails is an operating system processor, the whole computer can go down.

Symmetric Multiprocessing - Symmetric multiprocessing (SMP) technology is used to get higher levels of performance. In symmetric multiprocessing, any processor can run any type of thread. The processors communicate with each other through shared memory.

SMP systems provide better load-balancing and fault tolerance. Because the operating system threads can run on any processor, the chance of hitting a CPU bottleneck is greatly reduced. All processors are allowed to run a mixture of application and operating system code. A processor failure in the SMP model only reduces the computing capacity of the system.

SMP systems are inherently more complex than ASMP systems. A tremendous amount of coordination must take place within the operating system to keep everything synchronized. For this reason, SMP systems are usually designed and written from the ground up.

All processors of symmetric multiprocessing are peers; the relationship between processors of asymmetric multiprocessing is a master-slave relationship. More specifically, each CPU in symmetric multiprocessing runs the same copy of the OS, while in asymmetric multiprocessing, they split responsibilities typically, therefore each may have specialized (different) software and roles.