This invention relates to a personal computer having facility for ready variation in the amount of memory capability available on the microprocessor local bus. The personal computer has a microprocessor, a high speed local bus coupled to said microprocessor, a system bus, a bus controller coupled to and providing communication between the local bus and system bus, and a local bus memory facility coupled to and physically separable from the local bus. The local bus memory facility is provided by a substrate, preferably a printed circuit card, for mounting and providing coupling connections among components mounted thereon, at least one volatile memory component mounted on the card, and a memory controller mounted on the card and coupled to the volatile memory component, local bus and bus controller, with the memory controller regulating communications between the volatile memory component and microprocessor.