They are typically single user personal computers, although they have been adapted into multi-user models for special applications. There are hundreds of models of IBM compatible computers. Model 25, Model 30. Within each series, the models are also commonly referenced by their CPU clock rate . All IBM personal computers are software compatible with each other in general, but not every program will work in every machine.
Some programs are time sensitive to a particular speed class.
Older programs will not take advantage of newer higher-resolution display standards . It is determined by its clock rate and the number of bits it can process internally. It is also determined by the number of bits it transfers across its data bus . The second major performance factor is the speed of the hard disk . CAD and other graphics-intensive application programs can be sped up with the addition of a mathematics coprocessor , a chip which plugs into a special socket available in almost all machines.