Kenbak-1

Personal computer, invented in 1970
Kenbak-1
A Kenbak-1 at the Computer History Museum
DeveloperJohn Blankenbaker
ManufacturerKenbak Corporation
TypePersonal 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]

Since the Kenbak-1 was invented before the first microprocessor, the machine didn't 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
07 06 05 04 03 02 01 00 (bit position)
Main registers
A A
B B
X X (Index)
P Program Counter
Flags
000000 C O A flags
000000 C O B flags
000000 C O X flags
Input/Output
Output Lights
Input Switches

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:

  • Immediate (operand is in second byte of instruction)
  • Memory (second byte of instruction is the address of the operand)
  • Indirect (second byte of instruction is the address of the address of the operand)
  • Indexed (second byte of instruction is added to X to form the address of the operand)
  • Indirect Indexed (second byte of instruction points to a location which is added to X to form the address of the operand)

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]


Opcode matrix for the Kenbak-1 instruction set
High octal digits Low octal digit
0 1 2 3 4 5 6 7
00 HALT SFTR A1 SET 0 b0 XXX ADD A #XXX ADD A XXX ADD A (XXX) ADD A XXX, X ADD A (XXX), X
01 HALT SFTR A2 SET 0 b1 XXX SUB A #XXX SUB A XXX SUB A (XXX) SUB A XXX, X SUB A (XXX), X
02 HALT SFTR A3 SET 0 b2 XXX LOAD A #XXX LOAD A XXX LOAD A (XXX) LOAD A XXX, X LOAD A (XXX), X
03 HALT SFTR A4 SET 0 b3 XXX STORE A #XXX STORE A XXX STORE A (XXX) STORE A XXX, X STORE A (XXX), X
04 HALT SFTR B1 SET 0 b4 XXX JPD A ≠0 XXX JPD A =0 XXX JPD A <0 XXX JPD A ≥0 XXX JPD A >0 XXX
05 HALT SFTR B2 SET 0 b5 XXX JPI A ≠0 XXX JPI A =0 XXX JPI A <0 XXX JPI A ≥0 XXX JPI A >0 XXX
06 HALT SFTR B3 SET 0 b6 XXX JMD A ≠0 XXX JMD A =0 XXX JMD A <0 XXX JMD A ≥0 XXX JMD A >0 XXX
07 HALT SFTR B4 SET 0 b7 XXX JMI A ≠0 XXX JMI A =0 XXX JMI A <0 XXX JMI A ≥0 JMI A >0 XXX
10 HALT ROTR A1 SET 1 b0 XXX ADD B #XXX ADD B XXX ADD B (XXX) ADD B XXX, X ADD B (XXX), X
11 HALT ROTR A2 SET 1 b1 XXX SUB B #XXX SUB B XXX SUB B (XXX) SUB B XXX, X SUB B (XXX), X
12 HALT ROTR A3 SET 1 b2 XXX LOAD B #XXX LOAD B XXX LOAD B (XXX) LOAD B XXX, X LOAD B (XXX), X
13 HALT ROTR A4 SET 1 b3 XXX STORE B #XXX STORE B XXX STORE B (XXX) STORE B XXX, X STORE B (XXX), X
14 HALT ROTR B1 SET 1 b4 XXX JPD B ≠0 XXX JPD B =0 XXX JPD B <0 XXX JPD B ≥0 XXX JPD B >0 XXX
15 HALT ROTR B2 SET 1 b5 XXX JPI B ≠0 XXX JPI B =0 XXX JPI B <0 XXX JPI B ≥0 XXX JPI B >0 XXX
16 HALT ROTR B3 SET 1 b6 XXX JMD B ≠0 XXX JMD B =0 XXX JMD B <0 XXX JMD B ≥0 XXX JMD B >0 XXX
17 HALT ROTR B4 SET 1 b7 XXX JMI B ≠0 XXX JMI B =0 XXX JMI B <0 XXX JMI B ≥0 XXX JMI B >0 XXX
20 NOOP SFTL A1 SKP 0 b0 XXX ADD X #XXX ADD X XXX ADD X (XXX) ADD X XXX, X ADD X (XXX), X
21 NOOP SFTL A2 SKP 0 b1 XXX SUB X #XXX SUB X XXX SUB X (XXX) SUB X XXX, X SUB X (XXX), X
22 NOOP SFTL A3 SKP 0 b2 XXX LOAD X #XXX LOAD X XXX LOAD X (XXX) LOAD X (XXX) LOAD X (XXX), X
23 NOOP SFTL A4 SKP 0 b3 XXX STORE X #XXX STORE X XXX STORE X (XXX) STORE X XXX, X STORE X (XXX), X
24 NOOP SFTL B1 SKP 0 b4 XXX JPD X ≠0 XXX JPD X =0 XXX JPD X <0 XXX JPD X ≥0 XXX, X JPD X >0 XXX
25 NOOP SFTL B2 SKP 0 b5 XXX JPI X ≠0 XXX JPI X =0 XXX JPI X <0 XXX JPI X ≥0 XXX JPI X >0 XXX
26 NOOP SFTL B3 SKP 0 b6 XXX JMD X ≠0 XXX JMD X =0 XXX JMD X <0 XXX JMD X ≥0 XXX JMD X >0 XXX
27 NOOP SFTL B4 SKP 0 b7 XXX JMI X ≠0 XXX JMI X =0 XXX JMI X <0 XXX JMI X ≥0 XXX JMI X >0 XXX
30 NOOP ROTL A1 SKP 1 b0 XXX OR #XXX OR XXX OR (XXX) OR XXX, X OR (XXX), X
31 NOOP ROTL A2 SKP 1 b1 XXX — — — — —
32 NOOP ROTL A3 SKP 1 b2 XXX AND #XXX AND XXX AND (XXX) AND XXX, X AND (XXX), X
33 NOOP ROTL A4 SKP 1 b3 XXX LNEG #XXX LNEG XXX LNEG (XXX) LNEG XXX, X LNEG (XXX), X
34 NOOP ROTL B1 SKP 1 b4 XXX JPD UNC XXX JPD UNC XXX JPD UNC XXX JPD UNC XXX JPD UNC XXX
35 NOOP ROTL B2 SKP 1 b5 XXX JPI UNC XXX JPI UNC XXX JPI UNC XXX JPI UNC XXX JPI UNC XXX
36 NOOP ROTL B3 SKP 1 b6 XXX JMD UNC XXX JMD UNC XXX JMD UNC XXX JMD UNC XXX JMD UNC XXX
37 NOOP ROTL B4 SKP 1 b7 XXX JMI UNC XXX JMI UNC XXX JMI UNC XXX JMI UNC XXX JMI UNC XXX

See also

  • Datapoint 2200, a contemporary machine with alphanumeric screen and keyboard, suitable to run non-trivial application programs
  • Mark-8, 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
  • Gigatron TTL, a 21st-century implementation of a computer using small-scale integration parts

References

  1. ^ a b "Oral History of John Blankenbaker" (PDF). Computer History Museum. June 14, 2007.
  2. ^ "What was the First PC?". Retrieved October 25, 2022.
  3. ^ "PastExibits LINK - History of the PC". Retrieved October 13, 2022.
  4. ^ "The George R. Stibitz Computer Pioneer Award". Archived from the original on September 13, 2008. Retrieved August 5, 2008.
  5. ^ "Timeline of Computer History". Computer History Museum. Retrieved July 22, 2008.
  6. ^ BBC News, November 6, 2015
  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.
  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. ^ a b 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".
  15. ^ "Kenbak Theory of Operation Manual". p. 16.
  16. ^ "Official Kenbak-1 Reproduction Kit".
  17. ^ a b "Programming Reference Manual KENBAK-l Computer"

External links

  • Kenbak.com Comprehensive Kenbak-1 history and technical information
  • KENBAK-1 Computer Article
  • KENBAK-1 Computer – Official Kenbak-1 website at www.kenbak-1.info
  • Kenbak-1 Emulator – Kenbak-1 Emulator download
  • Kenbak 1 – Images and information at www.vintage-computer.com
  • Kenbak documentation at bitsavers.org