Stored program control system with switching between instruction word systems

A stored program control system comprising:

• an input/output device for exchanging data with an external apparatus,
• a main memory device for storing data and instruction words including a set of universal instruction words and a set of sequence instruction words, said set of sequence instruction words containing a portion of said set of universal instruction words and,
• a central processing unit including a plurality of general registers and means storing a program status word, said central processing unit controlling said input/output device and said main memory device, a portion of the bits of said program status word having a status representing selection of either said set of universal instruction words or said set of sequence instruction words, said central processing unit further including means responsive to a processed instruction word or to an internal processing sequence executed at the time of receipt of an interruption message for determining the status of said portion of bits and for selectively executing said set of universal instruction words or said set of sequence instruction words in accordance with the status of said bit portions of said program status word.