Harvest, also known as the IBM 7950, was a one-of-a-kind adjunct to the Stretch computer which was installed at the US National Security Agency. It was delivered in 1962 and operated until 1976, when it was decommissioned. It was built by IBM in Poughkeepsie, New York, and its electronics (fabricated of the same kind of discrete transistors used for Stretch) were physically about twice as big as the Stretch to which it was attached. Harvest added a small number of instructions to Stretch, and couldn't operate independently.

The equipment added to the Stretch computer consisted of the following special peripherials:

• IBM 7951 - Stream coprocessor
• IBM 7952 - High performance core storage
• IBM 7955 - Magnetic tape system also known as Tractor
• IBM 7959 - High speed I/O exchange

Harvest's most important mode of operation was called 'setup' mode, in which the processor was configured (with several hundred bits of information) and the processor then operated by streaming data from memory (possibly taking two streams from memory) and writing a separate stream back to memory. The two byte streams could be combined, used to find data in tables, or counted to determine the frequency of various values. A value could be anything from 1 to 16 contiguous bits, without regard to alignment, and the streams could be as simple as data laid out in memory, or data read repeatedly, under the control of multiply-nested "do"-loop descriptors which were interpreted by the hardware.

The Tractor tape system which was part of the Harvest system was unique for its time. It included 6 tape drives which handled 1.75 inch wide tape in cartridges, along with a library mechanism which could fetch a cartridge from a library, mount it on a drive, and restore it in the library. The transfer rates and library mechanism were balanced in performance such that the system could read two streams of data from tape, and write a third, for the entire capacity of the library, without any time wasted for tape handling.

Harvest was designed to be used for cryptanalysis. Two programming languages, Alpha and Beta (not be confused with Simula-inspired BETA programming language) were designed for programming it, and IBM provided a compiler for the former around the time the machine was delivered.

See also

• Cryptanalytic computer