In concentrated multiprocessor systems conforming to the presently disclosed modular architecture, a host processor and plural client processors are packaged in a single box containing a high speed (short length) bus connecting all of the processors, and data storage resources via the bus. The bus may be of a type commonly used in contemporary single computer systems; e.g. one conforming to PCI specifications. The host processor and associated resources are mounted directly on an integrated circuit motherboard containing the bus and card connectors attached to the bus. The card connectors removably receive integrated circuit cards containing individual client processors. In one embodiment, client processors are configured to be used as workstations or PC's—in a residence, office or small factory environment—relative to users and accessories remote from the system enclosure. In another embodiment, host and client processors are configured to operate as servers between the system and multiple data networks external to the system; the host and client subsystems thereby constituting a server “farm”.