1. A computer system having a plurality of system resources including processors, memory and I/O circuitry, the computer system comprising: an interconnection mechanism for electrically interconnecting the processors, memory and I/O circuitry so that each processor has electrical access to all of the memory and at least some of the I/O circuitry; a software mechanism for dividing the system resources into a plurality of partitions; at least one operating system instance running in each of a plurality of the partitions; and a processor designation storage device that stores a designation indicative of the operational status of a first processor relative to a first instance, the designation being used by the first instance in determining whether the first processor is currently available to it for processing activities.