The Kenbak-1 is considered by the

Computer History Museum The Computer History Museum (CHM) is a computer museum in Mountain View, California. The museum presents stories and artifacts of Silicon Valley and the Information Age, and explores the Digital Revolution, computing revolution and its impact ...

, the Mimms Museum of Technology and Art and the American Computer Museum to be the world's first "

personal computer A personal computer, commonly referred to as PC or computer, is a computer designed for individual use. It is typically used for tasks such as Word processor, word processing, web browser, internet browsing, email, multimedia playback, and PC ...

", invented by John Blankenbaker (born 1929) of Kenbak Corporation in 1970 and first sold in early 1971. Less than 50 machines were ever built, using Bud Industries enclosures as a

housing Housing refers to a property containing one or more Shelter (building), shelter as a living space. Housing spaces are inhabited either by individuals or a collective group of people. Housing is also referred to as a human need and right to ...

. The system first sold for US$750. Today, 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 A microprocessor is a computer processor (computing), processor for which the data processing logic and control is included on a single integrated circuit (IC), or a small number of ICs. The microprocessor contains the arithmetic, logic, a ...

, the machine did not have a one-chip CPU but was instead based purely on 7400-series TTL chips. The

8-bit In computer architecture, 8-bit integers or other data units are those that are 8 bits wide (1 octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers or data bu ...

machine offered 256

byte The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable un ...

s of

memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembe ...

, implemented on

Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California, and Delaware General Corporation Law, incorporated in Delaware. Intel designs, manufactures, and sells computer compo ...

's type 1404A silicon gate MOS

shift register A shift register is a type of digital circuit using a cascade of flip-flop (electronics), flip-flops where the output of one flip-flop is connected to the input of the next. They share a single clock signal, which causes the data stored in the syst ...

s. The

clock signal In electronics and especially synchronous digital circuits, a clock signal (historically also known as ''logic beat'') is an electronic logic signal (voltage or current) which oscillates between a high and a low state at a constant frequency and ...

period was 1

microsecond A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or 10−6 or ) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available. A microsecond is to one second, ...

(equivalent to a clock speed of 1

MHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base u ...

), 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 In computer programming, machine code is computer code consisting of machine language instructions, which are used to control a computer's central processing unit (CPU). For conventional binary computers, machine code is the binaryOn nonb ...

using an array of buttons and switches. Output consisted of a row of lights. Internally, the Kenbak-1 has a

serial computer A serial computer is a computer typified by bit-serial architecture i.e., internally operating on one bit or numerical digit, digit for each clock signal, clock cycle. Machines with serial main storage devices such as acoustic or magnetostrictive ...

architecture, processing one bit at a time."Kenbak Theory of Operation Manual"
"Official Kenbak-1 Reproduction Kit"

Technical description

Registers

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.

Addressing modes

Add, Subtract, Load, Store, Load Complement, 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."Programming Reference Manual KENBAK-l Computer"
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History

The Kenbak-1, released in early 1971, is considered by the

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. The 1975

Altair 8800 The Altair 8800 is a microcomputer introduced in 1974 by Micro Instrumentation and Telemetry Systems (MITS) based on the Intel 8080 CPU. It was the first commercially successful personal computer. Interest in the Altair 8800 grew quickly after i ...

had expansion slots, in contrast.

References

External links

Kenbak.com
Comprehensive Kenbak-1 history and technical information

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KENBAK-1 Computer
– Official Kenbak-1 website at www.kenbak-1.info
Kenbak-1 Emulator
– Kenbak-1 emulator in JavaScript
Kenbak-1 Emulator
– Kenbak-1 Emulator download
Kenbak 1
– Images and information at www.vintage-computer.com
Kenbak
documentation at bitsavers.org Early microcomputers Computer-related introductions in 1971 Serial computers 8-bit computers