Kenbak-1

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Kenbak-1
Kenbak1.jpg
A Kenbak-1 at the Computer History Museum
DeveloperJohn Blankenbaker
ManufacturerKenbak Corporation
Type Personal computer
Release date1971;53 years ago (1971)
Introductory priceUS$750(equivalent to $5,640 in 2023)
Discontinued1973 (1973)
Units sold44 [1]
Memory256  bytes of memory

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 Compliment, 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]


See also

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References

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  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.
  10. p. 52, "The First Personal Computer", Popular Mechanics, January 2000.
  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.
  13. Bill Wilson (6 November 2015). "The man who made 'the world's first personal computer'". BBC News.
  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"