The Kenbak-1 is a personal computer released in early 1971 by the Kenbak Corporation. Designed in 1970 by John Blankenbaker (born 1929), the Kenbak-1 is considered by several institutions, including the Computer History Museum, the Mimms Museum of Technology and Art and the American Computer Museum, to be the world's first commercially released personal computer. Less than 50 units were ever built, using Bud Industries enclosures as a housing. The system first sold for . , only 14 machines are known to exist worldwide, in the hands of various collectors and museums. Production of the Kenbak-1 stopped in 1973, 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.
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 7400-series TTL chips. The 8-bit machine offered 256 bytes of memory, implemented on Intel's type 1404A silicon gate MOS shift registers. 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.
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.
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.
Add, Subtract, Load, Store, Load Complement, And, and Or instructions operate between a register and another operand using five addressing modes:
The instructions are encoded in 8 bits, with a possible second byte providing an immediate value or address. Some instructions have multiple possible encodings.
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 .. 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. In contrast, the 1975 Altair 8800 had expansion slots, allowing the addition of memory and peripherals.