AN / FSQ - 31V The AN / FSQ - 31V was a computer made by IBM ( International Business Machines ) in 1960 and 1961 for the United States Air Force Strategic Air Command ( SAC ) . The IBM Model name for the machine was the 4020 . Three Q - 31 units were built . They were used as the Data Processing Center ( DPC ) portion of the SAC Automated Command and Control System . Locations . Two ( DPC 1 and DPC 2 ) were installed at SAC headquarters ( Bldg 500 ) at Offutt Air Force Base outside Omaha , Nebraska . One ( DPC 3 ) was installed in the Headquarters 15th Air Force Combat Operations Center at March Air Force Base , near Riverside , California . Another machine , designated the AN / FSQ - 32 , was installed at System Development Corporation ( SDC ) headquarters , Santa Monica , California and was used as a development machine for the compiler and operational software for the Q - 31s . Architecture . The system was divided into functional sections : Central Processing Unit . Memory was addressed by words , which were 48 bit s long . Each half word ( 24 bits ) had a parity bit , for a total storage size of 50 bits . Depending on addressing mode , each word could be viewed as either 1 48 - bit word , 2 - 24 bit half - words , 6 8 - bit characters ( EBCDIC encoded ) or 8 6 - bit bytes . A 6 - bit byte , as opposed to the 8 - bit byte in common use today , was common in IBM and other scientific computers of the time . The address space provided a maximum of 256K words . The ISA was rather complicated for its time . The instructions were a fixed length of one word providing 24 bits for the operation and 24 bits for the address . The address consisted of 18 bits ( 3 bytes ) for the memory address , with other bits used for the specification of index registers and indirect addressing . The operation field provided the operation code and a variety of modifiers . Some modifiers allowed instructions to operate only on specific bytes of a word or on specific bits of a byte without separate masking operations . Other modifiers allowed the single 48 - bit ALU to operate on a pair of 24 - bit operands to facilitate vector operations . Other parts of the CPU were some sense switches , which could be used to control various software functions , the run / halt switch , and a switch , amplifier , and speaker assembly , which could be used to provide audio feedback or even play music , by connecting one of four bits in the main accumulator which could then be toggled under software control at an appropriate rate to produce whatever tones one wanted . Someone in the software development division had produced a card deck on which was stored an executive that allowed selecting from a whole list of songs , including Christmas Carols , by setting the sense switches to a particular code , which would be printed out on the I / O Typewriter if a certain sense switch was on when the program was started . Memory . The Q - 31s were equipped with four 16 kiloword memory banks . The memory bank was oil and water cooled . Also considered as part of the memory subsystem in that they were addressed via fixed reserved memory addresses , were four 48 position switch banks , in which a short program could be inserted , and a plugboard , similar to the one used in IBM unit record equipment , that had the capacity of 32 word s , so longer bootstrap or diagnostic programs could be installed in plug panels which could then be inserted into the receptacle and used . This served as a primitive ROM . High - Speed Input / Output . The High - Speed I / O section provided interfaces to the Drum Memory system , which consisted of a control system , and two vertical drum memory devices . Each drum read and wrote 50 bits at a time in parallel so transferring data could be done quickly . The drums were organized as 17 fields with 8192 words per field for a total capacity of 139264 words . The motors that rotated the drums required 208 VAC at 45 Hz so a motor generator unit was required to change the frequency from 60 Hz . This added to the noise level in the computer room . Low - Speed Input / Output . The Low - Speed I / O section interfaced to several different devices :