A formal description of SYSTEM/360
Adin D. Falkoff, Kenneth E. Iverson, Edward H. Sussenguth · IBM Systems Journal · 1964
This paper presents a precise formal description of a complete computer system, the IBM SYSTEM/360 The description is functional: it describes the behavior of the machine as seen by the programmer, irrespective of any particular physical implemention, and expressly specifies the state of every register or facility accessible to the programmer for every moment of system operation at which this information is actually available.