1. A computer system comprising a microprocessor on a single integrated circuit chip connected to an external computer device via an adapter device; the integrated circuit chip having an on-chip CPU with a plurality of registers and a communication bus providing a parallel communication path between the CPU and a first memory local to the CPU, the integrated circuit further comprising an external communication port connected to the said bus on the integrated circuit chip, the port having an internal connection to the said bus of an internal parallel signal format and an external connection to the adapter unit of a first external format less parallel than the said internal format; the adapter device being connected to the external communication port with the first external format and to the external computer with a second external format having a higher latency than the first external format, the adapter device having an interface for translating between the first external format and the second external format; the external computer device having a second memory local to the external computer device; and the second memory being accessible by the CPU through the port, the port forming part of the memory address space of the CPU from which instructions may be fetched, whereby the port may be addressed by execution of an instruction by the CPU.