Abstract: Disclosed is a controller which functions to interconnect and control one or more digital devices such as magnetic discs, typewriters and other digital data processing equipment. The controller receives input signals and delivers output signals through interface vector (IV) buffer stores which connect to and from user devices. The logical state of the output signals in the buffer stores is determined by an instruction-controlled processor which accesses instructions from a memory. The instructions are processed in response to input signals (operands) from buffer stores and produce output signals (operands) to the buffer stores. The instruction fetching paths and the operand fetching and storing paths are separate. The controller includes apparatus and an instruction set which allows variable fields in the buffer stores to be addressed to provide source operands and to be addressed to store result operands after instruction execution.