1. A method in a computer system for using processor compatibility information to select a compatible processor for addition to a multiprocessor computer, the multiprocessor computer having at least one current processor in a CPU slot and having at least one additional CPU slot in which the new processor can be added, a processor having a revision number, the method comprising: obtaining the processor compatibility information that indicates the various model and revisions of processors that are compatible with each of a set of processor models and revisions; determining the number of current processors in the multiprocessor computer and the model and revision numbers of each processor by executing a computer program on the multiprocessor computer, the computer program directing each processor in the multiprocessor computer to execute at least one instruction that allows the model and revision number of the processor to be determined; and comparing the model and revision numbers of the current processors in the multiprocessor computer with the processor compatibility information to determine the revision numbers of processors that are compatible with all current processors.