Multiprocessing, Distributed Processing, and Networks: Tightly Coupled Systems (Multiprocessors)

Symmetric systems have some interesting features not found in asymmetric systems.

Efficiency

First, an observation about efficiency. One of the prime goals of symmetric systems is increased computational power. However, the communication overhead involved means that one cannot double computation power by simply going from one CPU to two. Experimental data indicates that 2 CPU's have roughly 1.8 times the power of 1, and 3 CPU's have roughly 2.1 times the power of 1 - though some systems have achieved better results (e.g 4 CPU's with 3.6 times the power of 1.)

The chief villain - but not the only one - is contention for access to shared memory.