Kenbak-1

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Kenbak-1
Kenbak-1 personal computer.jpg
A Kenbak-1 at Deutsches Museum, Munich
DeveloperJohn Blankenbaker
ManufacturerKenbak Corporation
Type Personal computer
Release date1971;54 years ago (1971)
Introductory priceUS$750(equivalent to $5,640 in 2023)
Discontinued1973 (1973)
Units sold44 [1]
Memory256  bytes of memory
A program running in a Kenbak-1 IDE/emulator. Click to start animation. Note that the program's sole use is to show lights being shifted. Kenbak IDE running a program.gif
A program running in a Kenbak-1 IDE/emulator. Click to start animation. Note that the program's sole use is to show lights being shifted.
Kenbakuino, an Arduino-based Kenbak-1 emulator Kenbakuino, an Arduino-based Kenbak emulator.jpg
Kenbakuino, an Arduino-based Kenbak-1 emulator

The Kenbak-1 is considered by the Computer History Museum, [2] the Computer Museum of America [3] and the American Computer Museum [4] to be the world's first "personal computer", [5] invented by John Blankenbaker (born 1929) of Kenbak Corporation in 1970 and first sold in early 1971. [6] Less than 50 machines were ever built, using Bud Industries enclosures as a housing. [1] The system first sold for US$750. [7] Today, only 14 machines are known to exist worldwide, [8] [9] in the hands of various collectors and museums. Production of the Kenbak-1 stopped in 1973, [10] as Kenbak failed and was taken over by CTI Education Products, Inc. CTI rebranded the inventory and renamed it the 5050, though sales remained elusive. [11]

Contents

Since the Kenbak-1 was invented before the first microprocessor, the machine did not have a one-chip CPU but was instead based purely on small-scale integration TTL chips. [12] The 8-bit machine offered 256  bytes of memory, [13] implemented on Intel's type 1404A silicon gate MOS shift registers. [14] The clock signal period was 1  microsecond (equivalent to a clock speed of 1  MHz), but the program speed averaged below 1,000 instructions per second due the many clock cycles needed for each operation and slow access to serial memory. [12]

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. [15] [16]

Technical description

Registers

Kenbak-1 registers
0706050403020100(bit position)
Main registers
AA
BB
XX (Index)
PProgram Counter
Flags
000000 C O A flags
000000COB flags
000000COX flags
Input/Output
OutputLights
InputSwitches

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, also known as the index register, turns the direct and indirect modes into indexed direct and indexed indirect modes. It also has a 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. [17]

Addressing modes

Add, Subtract, Load, Store, Load Complement, And, and Or instructions operate between a register and another operand using five addressing modes:

Instruction table

The instructions are encoded in 8 bits, with a possible second byte providing an immediate value or address. Some instructions have multiple possible encodings. [17]


History

The Kenbak-1, released in early 1971, is considered by the Computer History Museum to be the world's first personal computer. It was designed and invented by John Blankenbaker of Kenbak Corporation in 1970, and was first sold in early 1971. Unlike a modern personal computer, the Kenbak-1 was built of small-scale integrated circuits, and did not use a microprocessor. The system first sold for US$750. Only 44 machines were ever sold, though it's said 50 to 52 were built. In 1973, production of the Kenbak-1 stopped as Kenbak Corporation folded.

With a fixed 256 bytes of memory, input and output restricted to lights and switches (no ports or serial output), and no possible way to extend its capabilities, the Kenbak-1 was only really useful for educational use.

256 bytes of memory, 8 bit word size, and I/O limited to switches and lights on the front panel are also characteristics of the 1975 Altair 8800, whose fate was diametrically opposed to that of the Kenbak. However, there were three major differentiating factors between the Altair and the Kenbak which led to the later Altair 8800 selling over 25000 units and influencing many, while the Kenbak-1 only sold 44, and influenced mostly no one.

If the Kenbak-1 were advertised better, and the machine had at least one serial port to make it more useful, it may have done very well at its price-point of $750 in 1971, which no other Turing-complete computer on the market came close to. However, it would not be very long before personal computers based on the much more capable Intel 8008 would come to market, followed shortly after once again by the ten-times-as-fast Intel 8080, in the highly-expandable Altair 8800.

See also

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References

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  7. "Kenbak-1 The Training Computer". Computerworld. November 17, 1971. p. 43. Retrieved May 25, 2014.
  8. "List of Extant Kenbak-1 Computers". Kenbak.com. Retrieved 13 October 2022.
  9. "Kenbak-1". Computer Museum of Nova Scotia. Retrieved 19 November 2015.
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  11. Robert R Nielsen, Snr (2005). "Inside the Kenbak-1". YouTube . Archived from the original on 2021-12-13. Retrieved 8 November 2015.
  12. 1 2 Erik Klein. "Kenbak Computer Company Kenbak-1". Old-computers.com. Retrieved May 25, 2014.
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  14. "Technical". www.kenbak-1.net.
  15. "Kenbak Theory of Operation Manual". p. 16.
  16. "Official Kenbak-1 Reproduction Kit".
  17. 1 2 "Programming Reference Manual KENBAK-l Computer"