Abstract: The invention relates to a computer in which control means provide for high speed context switching. In a more specific aspect, the invention involves an arithmetic unit in which a workspace pointer register and control means operable on an interrupt store the contents of the workspace pointer in an element of a workspace in memory designated by the interrupt program and store in the workspace pointer register the address of the first element of the interrupt program workspace.A first register stores the address of a first element of a set of dedicated workspace elements in main memory.A second register stores the memory address of a current instruction of a problem program.