This unit is responsible for all events inside the computer. It controls all internal and external devices, performs arithmetic and logic operations. The operations a microprocessor performs are called the instruction set of this processor. The more complicated the instruction set is, the slower the CPU works.
Processors differ from one another by the instruction set.
If the same program can run on two different computer brands they are said to be compatible . Programs written for IBM compatible computers will not run on Apple computers because these two architectures are not compatible. There is an exception to this rule. These programs are called software emulators . Although software emulators allow the CPU to run incompatible programs they severely slow down the performance.