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The CDC 6600 was a mainframe computer manufactured by Control Data Corporation, designed by Seymour Cray [1], and flagship of the CDC 6000 series, first delivered in 1964. It is generally considered to be the first successful supercomputer, outperforming its fastest predecessor, IBM 7030 Stretch, by about three times. Its circuits were cooled by extensive chilled water plumbing. It remained the world's fastest computer from 1964 to 1969, when it relinquished that status to its successor, the CDC 7600 [2].
CDC 6600 [3].

CDC 6400

The CDC 6400 was architecturally compatible with the CDC 6600. In contrast to the 6600, which had 10 parallel functional units which could work on multiple instructions at the same time, the 6400 had a unified arithmetic unit, which could only work on a single instruction at a time. This resulted in a slower, lower-performance CPU, but one that cost significantly less [4].


The 6600 can be considered as first RISC architecture. The central processor had 60-bit words, the peripheral processors had 12-bit words. CDC used the term byte to refer to 12-bit entities used by peripheral processors - characters were 6-bit, and central processor instructions were either 15 bits, or 30 bits with a signed 18-bit address field, the latter allowing for a directly addressable memory space of 128K words of central memory (converted to modern terms, with 8-bit bytes, this is 0.94 MiB). It had eight general purpose 60-bit registers X0 through X7, eight 18-bit address registers A0 through A7, and eight 18-bit scratchpad registers B0 through B7. B0 was held permanently at zero by the hardware; many programmers found it useful to set B1 to 1 and then treat it as similarly inviolate [5]. The signed nature of the address registers limited an individual program to 128K words.

Population Count

The NSA had demanded the implementation of the population count opcode for cryptanalysis and cryptography purpose, which was implemented by using the hardware of the divide unit [6].

Chess Programs

Several early chess programs ran on the CDC 6600, notably Chess 4.0 and Beal during the WCCC 1974

See also

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External Links


  1. ^ A Seymour Cray Perspective by Gordon Bell, University of Minnesota, November 10, 1997
  2. ^ File:CDC 6600.jc.jpg - Wikipedia
  3. ^ Supercomputer - The Beginnings | Flickr - Fotosharing by Jitze Couperus
  4. ^ CDC 6400 from Wikipedia
  5. ^ CDC 6600 from Wikipedia
  6. ^ Sideways Add / Population Count by Jitze Couperus and Steve Bellovin et al., cryptography@c2.net, January 28, 1999

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