For many years, the speed of computer processors increased through improvements in the architecture and clock speed of processors. However, in recent years, chip manufacturers have reached a limit in how small they can make the transistors inside CPUs without them overheating. Therefore, using multiple processors, or multiprocessing, has become the next step in increasing computing performance.
Multiprocessing can be implemented in two different ways: 1) using more than one physical processor, or 2) using a processor with multiple cores. For example, early Power Mac G5 computers had multiple physical processors, each with their own heat sink and frontside bus. When Apple switched to using Intel processors in 2006, they began using dual-core processors. These chips look like a single processor, but act as two. Now, some machines like the Mac Pro, have quad-core processors, which include four processing cores. Some Mac Pros even have two physical quad-core processors, giving the computer a total of eight processors. Most Windows and Linux-based PCs now use multi-core processors as well.
While multiprocessing sounds like a logical choice for improving computing performance, it must be supported by the computer's operating system in order to work correctly. Fortunately, current versions of both Windows and Mac OS X fully support multiprocessing. This means they can manage multiple processors as one CPU, dividing the processing load between them. Still, not all tasks can be split equally between two or more processors. Therefore, while multiprocessing may increase a computer's speed, it does not typically improve performance by the exact factor of processors in the machine.