Intel 8008

Intel 8008
source
Name	Intel 8008
Caption	An Intel C8008-1 microprocessor
Produced	Start 1972
Designer	Intel, Computer Terminal Corporation
Data-width	8-bit
Address-width	14-bit
Transistors	3,500
Process	10 μm
Frequency	0.5–0.8 MHz
Package	18-pin DIP
Predecessor	Intel 4004
Successor	Intel 8080

Intel 8008. The Intel 8008 is an early 8-bit microprocessor designed and manufactured by Intel and introduced in April 1972. It was the world's first 8-bit microprocessor, developed initially for the Computer Terminal Corporation as the heart of their Datapoint 2200 programmable terminal. Although not directly used in that system, its release marked a pivotal step in the evolution of personal computing and embedded control systems.

History and development

The origins of the 8008 are intertwined with the Datapoint 2200, a pioneering programmable terminal from Computer Terminal Corporation (CTC). In 1969, CTC approached both Intel and Texas Instruments to develop a single-chip CPU for their terminal. While Texas Instruments produced a chip that was not adopted, Intel's design, led by engineers including Ted Hoff, Stanley Mazor, and Federico Faggin, evolved into the 8008. The project was initially separate from the development of the Intel 4004, which was being created for Busicom. Due to design complexities and a tight schedule, CTC ultimately chose not to use the chip, opting for a TTL-based processor instead. Intel retained the rights to the design, commercializing it in 1972. This project established critical design methodologies that directly influenced the architecture of the more successful Intel 8080.

Architecture and design

The architecture of the 8008 is a parallel 8-bit design with a 14-bit address bus, allowing it to access up to 16 KB of memory. Its instruction set comprised 48 instructions and it featured seven 8-bit registers, though it lacked a dedicated stack pointer or sophisticated interrupt handling. The processor utilized a multi-chip support system, requiring external TTL circuits for functions like clock generation and system control. The ALU performed operations on 8-bit data, and the design employed a PMOS logic process. Its von Neumann architecture meant program and data shared the same memory space. The instruction cycle was tied to a slower clock, requiring multiple cycles to execute a single instruction, which impacted overall performance.

Technical specifications

Fabricated on a 10 μm PMOS process, the 8008 contained approximately 3,500 transistors. It was packaged in an 18-pin DIP, which limited its I/O and control capabilities, necessitating complex external circuitry. The processor operated at clock speeds between 0.5 and 0.8 MHz, with a typical instruction execution time of 20 μs. Its 14-bit address bus supported a maximum of 16 KB of memory. The chip required three supply voltages (+5V, -5V, +9V) and consumed significant power. It supported a basic set of 48 instructions and could perform around 60,000 operations per second. The limited pin count meant the lower 8 address bits were multiplexed with the 8-bit data bus.

Impact and legacy

Although not a major commercial success itself, the 8008 had a profound impact on the microprocessor industry. It demonstrated the viability of an 8-bit CPU on a single chip, influencing a generation of early microcomputers and control systems. It was used in some of the earliest personal computers, including the SCELBI-8H and the Mark-8, sparking interest among hobbyists. The design experience gained was directly applied by Intel to create the vastly more influential Intel 8080, which became the heart of the Altair 8800. The 8008 also found early use in traffic light controllers, calculators, and various embedded system applications, proving the concept of microprocessor-based control.

Variants and derivatives

The primary variant was the 8008-1, which had a specified maximum clock speed of 0.8 MHz. Several second-source manufacturers produced compatible versions, including National Semiconductor with their IMP-8 and Intersil with the IM6100, which was a CMOS implementation. The architecture was also implemented in bit-slice form using the Intel 3000 family. While not a direct variant, the instruction set and core architectural concepts were evolved and expanded into the Intel 8080, which maintained software compatibility at the assembly level for a subset of instructions. Other companies, like Signetics, also produced pin-compatible versions for the industrial market.

Category:Intel microprocessors Category:8-bit microprocessors Category:1972 in computing