Abstract: A data processing system has a working or buffer store connected between a main or bulk store and a vector processing unit. The buffer store contains one or more vitual vector registers operable under user control in register-to-register vector operations. A user instruction specifies the length of a vector operand to be processed, the type of operation to be performed, and which vector registers will be used. Vector processing is controlled by a series of programs defined at the code level of the processing unit where for a given function or operation, the same program is used for both register-to-register and storage-to-storage processing. The latter processing is controlled by passing predetermined parameters to the program whereas register-to-register processing is controlled by passing parameters generated in response to user program instructions.