BESYS (Bell Operating System) was an early computing environment originally implemented as a batch processing operating system in 1957 at Bell Labs for the IBM 704 computer.

BESYS (Bell Operating System)
DeveloperBell Labs
Written inIBM's FORTRAN and North American's Symbolic Assembly Program (SAP)
Working stateDiscontinued
Initial release1957 (1957)
Latest releaseBE90 / 1968 (1968)
PlatformsIBM 704
History of IBM mainframe operating systems


The system was developed because Bell recognized a "definite mismatchbetween the 704's internal speed, the sluggishness of its on-line unit-record equipment, and the inherent slowness of manual operations associated with stand-alone use."[1]

The goals of the system were:

The initial version of the system BESYS-1 was in use by October 16, 1957.[1] It was created by George H. Mealy and Gwen Hansen with Wanda Lee Mammel under the guidance of Victor A. Vyssotsky and utilized IBM's FORTRAN and North American's Symbolic Assembly Program (SAP) programming languages. It was designed to efficiently deal with a large number of jobs originating on punched cards and producing results suitable for printing on paper and punched cards. The system also provided processing capabilities for data stored on magnetic tapes and magnetic disk storage units. Typically punched card and print processing was handled off line by peripheral Electronic Accounting Machines, IBM 1401 computers, and eventually direct coupled computers.

The first system actually used at Bell Labs was BESYS-2. The system was resident on magnetic tape, and occupied the lowest 64 (36-bit) words and the highest4 K words of memory. The upper 4 K words held the resident portion of the monitor, and could be partially swapped to magnetic drum to free up additional core for the user program if needed.[1]

"BESYS was a complex software package that provided convenient input/output and integrated disk file storage facilities."[2]

Internal use

BESYS was used extensively by many departments of Bell Labs for over a decade. It was made available through the SHARE organization to others without charge or formal technical support.

BESYS versions

Versions of the BESYS environment (BESYS-3 (1960), BESYS-4 (1962), BESYS-5 (1963), BESYS-7 (1964), and BE90 (1968)[1]) were implemented as the underlying computers transitioned through the IBM 709X family. BESYS development was discontinued when Bell Labs moved to the IBM System/360 in 1969. Throughout this period the head of the BESYS development project was George L. Baldwin.


  1. Drummond, R.E, (1987). "BESYS Revisited" (PDF). AFIPS Conference Proceedings. 56: 805–814.CS1 maint: extra punctuation (link)
  2. Belzer, Jack; Holzman, Albert G.; Kent, Allen (March 1, 1976). Encyclopedia of Computer Science and Technology: Volume 3. CRC Press. p. 210. Retrieved May 26, 2017.
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