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Lot 76
21 September 2015, 13:00 EDT
New York

Sold for US$31,250 inc. premium

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Prototype Kenbak-1 Computer built by John Blankenbaker, 8-bit, comprising motherboard with 132 integrated circuits, 2 power supplies (for +5 volts and -12 volts), 2 MOS shift registers (1024 bits each), and cooling fan; in original customized steel case with 3-prong power connector, the front panel with a toggle power switch, 12 incandescent lights, 15 push-buttons and various lettering including the name "KENBAK-1." Approximately 19.25 x 11.5 x 4.25 inches. Overall excellent condition and operational as of July, 2015.
WITH: Binder of documentation including the Programming Reference Manual. Kenbak-1 Computer. [Los Angeles, 1971]; "Installation & Maintenance" and "Theory of Operation" manual; original coding sheets, reviews, purchase guides, etc.
AND: Laboratory Exercises. Kenbak-1 Computer. [Los Angeles, 1971.] Spiral-bound.
Provenance: Directly from the collection of the inventor, John Blankenbaker (b.1929).

FIRST VERSION OF THE "THE WORLD'S FIRST PERSONAL COMPUTER," so deemed by a panel of judges including Steve Wozniak at The Computer Museum (Boston) in 1987. The present example is the prototype from the collection of the inventor, the very one which was demonstrated in the spring of 1971 at a high school teacher's convention in southern California.

John Blankenbaker first began to imagine personal computers in the late 1950s while working for Hughes Aircraft Company. His target was a programmable computer for $500. However, it was not until 1970, finding himself unemployed, that he pursued the project in earnest. In his own words, "My criteria for the computer were low cost, educational, and able to give user satisfaction with simple programs ... It should demonstrate as many programming concepts as was possible. Because of the small size, the native language of the unit would be the machine language. Above all, it had to be a stored program machine in the von Neumann sense" ( Designed in the autumn of 1970, the Kenbak-1 pre-dates the invention of microprocessers and obviates the principles of microprogramming completely, using TTL logic instead. To keep costs low, switches and lights are the input/output of the machine. It has 256 bytes of memory and a clock speed of about 1 MHz.

THIS PROTOTYPE IS THE VERY ONE USED IN THE FIRST DEMONSTRATION OF A COMMERCIAL PERSONAL COMPUTER in May of 1971 at an Anaheim convention of high school mathematics teachers. It has the same functionality as the later production models, but differs in several respects: the red "enter" button in the prototype was replaced by a memory lock switch; the position of the labels was changed to above the buttons for better legibility; and, thirdly, the production models had a slot for an unrealized punch card reader.

Blankenbaker built the computers at his home in Los Angeles (purchased with a VA loan) and the first advertisement for Kenbak-1's appeared in the September 1971 issue of Scientific American at a price of $750, again using this very machine as the illustration. In retrospect, Blankenbaker acknowledged that he should have followed his first instincts to market the computer to hobbyists rather than educators. He had envisaged a newsletter with games and programs. A few of the fun programs that run on the Kenbak-1 are "Is it a legitimate date and if so what day of the week did it fall on?", "I predict your next guess will be..." and "Three dimensional tic-tac-toe." In the event, about 40 units were sold over the next year, chiefly to schools, until the company was sold in early 1973. See Computer History Museum, "Oral History of John Blankenbaker," interviewed by Lee Felsenstein, 2007;; and "What was the First PC?" on

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