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A Kenbak-1 at the Computer History Museum
DeveloperJohn Blankenbaker
ManufacturerKenbak Corporation
TypePersonal computer
Release date1971; 51 years ago (1971)
Introductory priceUS$750 (equivalent to $5,020 in 2021)
Discontinued1973 (1973)
Units sold44[1]
Memory256 bytes of memory

The Kenbak-1 is considered by the Computer History Museum and the American Computer Museum[2] to be the world's first "personal computer",[3] invented by John V. Blankenbaker (born 1929) of Kenbak Corporation in 1970, and first sold in early 1971.[4] Only 50 machines were ever built using Bud Industries enclosures as its housing.[1] The system first sold for US$750.[5] Today, only 14 machines are believed to exist worldwide,[6] in the hands of various collectors. Production of the Kenbak-1 stopped in 1973[7] as Kenbak failed, and was taken over by CTI Education Products, Inc. CTI rebranded the inventory and renamed it the H5050, though sales remained elusive.[8]

Since the Kenbak-1 was invented before the first microprocessor, the machine didn't have a one-chip CPU but instead was based purely on small-scale integration TTL chips.[9] The 8-bit machine offered 256 bytes of memory,[10] implemented on Intel's type 1404 silicon gate MOS shift registers.[11] The instruction cycle time was 1 microsecond (equivalent to an instruction clock speed of 1 MHz), but actual execution speed averaged below 1000 instructions per second due to architectural constraints such as slow access to serial memory.[9]

The machine was programmed in pure machine code using an array of buttons and switches. Output consisted of a row of lights.

Internally, the Kenbak-1 has a serial computer architecture, processing one bit at a time.[12][13]

Technical description[edit]


The Kenbak-1 has a total of nine registers. All are memory mapped. It has three general-purpose registers: A, B and X. Register A is the implicit destination of some operations. Register X is also known as the index register and turns the direct and indirect modes into indexed direct and indexed indirect modes. It also has program counter, called Register P, three "overflow and carry" registers for A, B and X respectively as well as an Input Register and an Output Register.[14]

Instruction table[edit]

The instructions are encoded in 8 bits, with a possible second byte providing an immediate value or address. Some instructions have multiple possible encodings. [14]

See also[edit]

  • Datapoint 2200, a contemporary machine with alphanumeric screen and keyboard, suitable to run non-trivial application programs.
  • Mark-8 The Mark-8 was designed by graduate student Jonathan A. Titus and announced as a 'loose kit' in the July 1974 issue of Radio-Electronics magazine.
  • Altair 8800, a very popular 1975 microcomputer that provided the inspiration for starting Microsoft.


  1. ^ a b "Oral History of John Blankenbaker" (PDF). Computer History Museum. June 14, 2007.
  2. ^ "The George R. Stibitz Computer Pioneer Award". Archived from the original on September 13, 2008. Retrieved August 5, 2008.
  3. ^ "Timeline of Computer History". Computer History Museum. Retrieved July 22, 2008.
  4. ^ BBC News, November 6, 2015
  5. ^ "Kenbak-1 The Training Computer". Computerworld. November 17, 1971. p. 43. Retrieved May 25, 2014.
  6. ^ "Kenbak-1". Computer Museum of Nova Scotia. Retrieved 19 November 2015.
  7. ^ p. 52, "The First Personal Computer", Popular Mechanics, January 2000.
  8. ^ Robert R Nielsen, Snr (2005). "Inside the Kenbak-1". YouTube. Archived from the original on 2021-12-13. Retrieved 8 November 2015.
  9. ^ a b Erik Klein. "Kenbak Computer Company Kenbak-1". Retrieved May 25, 2014.
  10. ^ Bill Wilson (6 November 2015). "The man who made 'the world's first personal computer'". BBC News.
  11. ^ "Technical".
  12. ^ "Kenbak Theory of Operation Manual". p. 16.
  13. ^ "Official Kenbak-1 Reproduction Kit".
  14. ^ a b "Programming Reference Manual KENBAK-l Computer"

External links[edit]