The Intel 8008 ("''eight-thousand-eight''" or "''eighty-oh-eight''") is an early
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 ...
microprocessor capable of addressing 16 KB of memory, introduced in April 1972. The 8008 architecture was designed by
Computer Terminal Corporation (CTC) and was implemented and manufactured by
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 ...
. While the 8008 was originally designed for use in CTC's
Datapoint 2200
The Datapoint 2200 was a mass-produced programmable terminal usable as a computer, designed by Computer Terminal Corporation (CTC) founders Phil Ray and Gus Roche and announced by CTC in June 1970 (with units shipping in 1971). It was initially ...
programmable terminal, an agreement between CTC and Intel permitted Intel to market the chip to other customers after
Seiko
, commonly known as Seiko ( , ), is a Japanese maker of watches, clocks, electronic devices, and semiconductors. Founded in 1881 by Kintarō Hattori in Tokyo, Seiko introduced the world's first commercial quartz wristwatch in 1969.
Seiko is ...
expressed an interest in using it for a
calculator
An electronic calculator is typically a portable electronic device used to perform calculations, ranging from basic arithmetic to complex mathematics.
The first solid-state electronic calculator was created in the early 1960s. Pocket-si ...
.
History
In order to address several issues with the
Datapoint 3300
The DataPoint 3300 was the first computer terminal manufactured by Computer Terminal Corporation, later renamed Datapoint, announced in 1967 and shipping in 1969. Since this terminal was intended to replace a teleprinter such as those made by T ...
, including excessive heat radiation,
Computer Terminal Corporation (CTC) designed the architecture of the 3300's planned successor with a CPU as part of the internal circuitry re-implemented on a single chip. Looking for a company able to produce their chip design, CTC co-founder Austin O. "Gus" Roche turned to Intel, then primarily a vendor of memory chips.
Roche met with
Bob Noyce, who expressed concern with the concept;
John Frassanito
John is a common English name and surname:
* John (given name)
* John (surname)
John may also refer to:
New Testament
Works
* Gospel of John, a title often shortened to John
* First Epistle of John, often shortened to 1 John
* Second Ep ...
recalls that: Another major concern was that Intel's existing customer base purchased their memory chips for use with their own processor designs; if Intel introduced their own processor, they might be seen as a competitor, and their customers might look elsewhere for memory. Nevertheless, Noyce agreed to a US$50,000 development contract in early 1970 ().
Texas Instruments
Texas Instruments Incorporated (TI) is an American multinational semiconductor company headquartered in Dallas, Texas. It is one of the top 10 semiconductor companies worldwide based on sales volume. The company's focus is on developing analog ...
(TI) was also brought in as a second supplier.
In December 1969, Intel engineer
Stan Mazor and a representative of CTC met to discuss options for the logic chipset to power a new CTC business terminal. Mazor, who had been working with
Ted Hoff on the development of the
Intel 4004
The Intel 4004 was part of the 4 chip MCS-4 micro computer set, released by the Intel, Intel Corporation in November 1971; the 4004 being part of the first commercially marketed microprocessor chipset, and the first in a long line of List of I ...
, proposed that a one-chip programmable microprocessor might be less cumbersome and ultimately more cost effective than building a custom logic chipset. CTC agreed and development work began on the chip, which at the time was known as the 1201.
TI was able to make samples of the 1201 based on Intel drawings, calling it the TMX 1795. These proved to be buggy and were rejected. Intel's own versions were delayed. CTC decided to re-implement the new version of the terminal using
serial discrete
TTL instead of waiting for a single-chip CPU. The new system was released as the
Datapoint 2200
The Datapoint 2200 was a mass-produced programmable terminal usable as a computer, designed by Computer Terminal Corporation (CTC) founders Phil Ray and Gus Roche and announced by CTC in June 1970 (with units shipping in 1971). It was initially ...
in the spring of 1970, with their first sale to
General Mills
General Mills, Inc. is an American multinational corporation, multinational manufacturer and marketer of branded ultra-processed consumer foods sold through retail stores. Founded on the banks of the Mississippi River at Saint Anthony Falls in ...
on 25 May 1970.
CTC paused development of the 1201 after the 2200 was released, as it was no longer needed. Later in early 1971, Seiko approached Intel, expressing an interest in using the 1201 in a scientific calculator, likely after seeing the success of the simpler 4004 used by Busicom in their business calculators.
A small re-design followed, under the leadership of
Federico Faggin
Federico Faggin (, ; born 1 December 1941) is an Italian-American physicist, engineer, inventor and entrepreneur. He is best known for designing the first commercial microprocessor, the Intel 4004. He led the 4004 (MCS-4) project and the desig ...
, the designer of the
4004, now project leader of the 1201, expanding from a 16-pin to 18-pin design, and the new 1201 was delivered to CTC in late 1971.
By that point, CTC had once again moved on, this time to the parallel-architecture
Datapoint 2200 II
Datapoint Corporation, originally known as Computer Terminal Corporation (CTC), was a computer company based in San Antonio, Texas, United States. Founded in July 1968 by Phil Ray and Gus Roche, its first products were, as the company's initial ...
, which was faster than the 1201. CTC voted to end their involvement with the 1201, leaving the design's intellectual property to Intel instead of paying the $50,000 contract. Intel renamed it the 8008 and put it in their catalog in April 1972 priced at US$120 (). This renaming tried to ride off the success of the 4004 chip, by presenting the 8008 as simply a 4 to 8 port, but the 8008 is ''not'' based on the
4004. The 8008 went on to be a commercially successful design. This was followed by the popular
Intel 8080
The Intel 8080 is Intel's second 8-bit computing, 8-bit microprocessor. Introduced in April 1974, the 8080 was an enhanced successor to the earlier Intel 8008 microprocessor, although without binary compatibility.'' Electronic News'' was a week ...
, and then the hugely successful
Intel x86
x86 (also known as 80x86 or the 8086 family) is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel, based on the 8086 microprocessor and its 8-bit-external-bus variant, the 8088. The ...
family.
In the UK, a team at S. E. Laboratories Engineering (EMI) led by Tom Spink in 1972 built a microcomputer based on a pre-release sample of the 8008. Joe Hardman extended the chip with an external stack. This, among other things, gave it power-fail save and recovery. Joe also developed a direct screen printer. The operating system was written using a meta-assembler developed by L. Crawford and J. Parnell for a
Digital Equipment Corporation
Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president until ...
PDP-11
The PDP–11 is a series of 16-bit minicomputers originally sold by Digital Equipment Corporation (DEC) from 1970 into the late 1990s, one of a set of products in the Programmed Data Processor (PDP) series. In total, around 600,000 PDP-11s of a ...
. The operating system was burnt into a PROM. It was interrupt-driven, queued, and based on a fixed page size for programs and data. An operational prototype was prepared for management, who decided not to continue with the project.
The 8008 was the CPU for the very first commercial non-calculator
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 ...
s (excluding the Datapoint 2200 itself): the US
SCELBI
SCELBI was an early model of microcomputer based on the Intel 8008 processor. The company SCELBI (derived from SCientific-ELectronics-BIology) Computer Consulting in 1973, by Nat Wadsworth. The SCELBI 8H was marketed in 1974 and was delivered eith ...
kit and the pre-built French
Micral N and Canadian
MCM/70
The MCM/70 is a pioneering microcomputer first built in 1973 in Toronto, Ontario, Canada and released the next year. This makes it one of the first microcomputers in the world, the second to be shipped in completed form, and the first portable comp ...
. It was also the controlling microprocessor for the first several models in Hewlett-Packard's
2640 family of computer terminals.
In 1973, Intel offered an
instruction set simulator
An instruction set simulator (ISS) is a simulation model (abstract), model, usually coded in a high-level programming language, which mimics the behavior of a mainframe or microprocessor by "reading" instructions and maintaining internal variables ...
for the 8008 named INTERP/8.
[ (132 pages)] It was written in
FORTRAN IV by
Gary Kildall
Gary Arlen Kildall (; May 19, 1942 – July 11, 1994) was an American computer scientist and microcomputer entrepreneur. During the 1970s, Kildall created the CP/M operating system among other operating systems and programming tools, and s ...
while he worked as a consultant for Intel.
[ (2 pages)]
Design

The 8008 was implemented in 10
μm silicon-gate enhancement-mode
PMOS logic
PMOS or pMOS logic, from p-channel metal–oxide–semiconductor, is a family of digital circuits based on p-channel, enhancement mode metal–oxide–semiconductor field-effect transistors (MOSFETs). In the late 1960s and early 1970s, PMOS ...
. Initial versions could work at clock frequencies up to 0.5 MHz. This was later increased in the 8008-1 to a specified maximum of 0.8 MHz. Instructions take between 3 and 11 T-states, where each T-state is 2 clock cycles.
Register–register loads and ALU operations take 5T (20 μs at 0.5 MHz), register–memory 8T (32 μs), while calls and jumps (when taken) take 11 T-states (44 μs).
The 8008 is a little slower in terms of
instructions per second
Instructions per second (IPS) is a measure of a computer's Central processing unit, processor speed. For complex instruction set computers (CISCs), different Machine code, instructions take different amounts of time, so the value measured depen ...
(36,000 to 80,000 at 0.8 MHz) than the 4-bit
Intel 4004
The Intel 4004 was part of the 4 chip MCS-4 micro computer set, released by the Intel, Intel Corporation in November 1971; the 4004 being part of the first commercially marketed microprocessor chipset, and the first in a long line of List of I ...
and
Intel 4040
The Intel 4040 ("''forty-forty''") is the second 4-bit microprocessor designed and manufactured by Intel. Introduced in 1974 as a successor to the Intel 4004, the 4040 was produced with a 10 μm process and includes silicon gate enhancem ...
. but since the 8008 processes data 8 bits at a time and can access significantly more RAM, in most applications it has a significant speed advantage over these processors. The 8008 has 3,500
transistor
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...
s.
The chip, limited by its 18-pin
DIP, has a single 8-bit bus working triple duty to transfer 8 data bits, 14 address bits, and two status bits. The small package requires about 30 TTL support chips to interface to memory. For example, the 14-bit address, which can access "16 K × 8 bits of memory", needs to be latched by some of this logic into an external memory address register (MAR). The 8008 can access 8
input ports and 24 output ports.
For controller and
CRT terminal use, this is an acceptable design, but it is rather cumbersome to use for most other tasks, at least compared to the next generations of microprocessors. A few early computer designs were based on it, but most would use the later and greatly improved
Intel 8080
The Intel 8080 is Intel's second 8-bit computing, 8-bit microprocessor. Introduced in April 1974, the 8080 was an enhanced successor to the earlier Intel 8008 microprocessor, although without binary compatibility.'' Electronic News'' was a week ...
instead.
Related processor designs
The subsequent 40-pin
NMOS Intel 8080
The Intel 8080 is Intel's second 8-bit computing, 8-bit microprocessor. Introduced in April 1974, the 8080 was an enhanced successor to the earlier Intel 8008 microprocessor, although without binary compatibility.'' Electronic News'' was a week ...
expanded upon the 8008 registers and instruction set and implements a more efficient external bus interface (using the 22 additional pins). Despite a close architectural relationship, the 8080 was not made binary compatible with the 8008, so an 8008 program would not run on an 8080. However, as two different assembly syntaxes were used by Intel at the time, the 8080 could be used in an 8008 assembly-language backward-compatible fashion.
The
Intel 8085
The Intel 8085 ("''eighty-eighty-five''") is an 8-bit microprocessor produced by Intel and introduced in March 1976. It is software-binary-code compatibility, binary compatible with the more-famous Intel 8080. It is the last 8-bit microprocesso ...
is an electrically modernized version of the 8080 that uses
depletion-mode transistors and also added two new instructions.
The
Intel 8086
The 8086 (also called iAPX 86) is a 16-bit computing, 16-bit microprocessor chip designed by Intel between early 1976 and June 8, 1978, when it was released. The Intel 8088, released July 1, 1979, is a slightly modified chip with an external 8-b ...
, the original x86 processor, is a non-strict extension of the 8080, so it loosely resembles the original Datapoint 2200 design as well. Almost every Datapoint 2200 and 8008 instruction has an equivalent not only in the instruction set of the 8080, 8085, and
Z80
The Zilog Z80 is an 8-bit microprocessor designed by Zilog that played an important role in the evolution of early personal computing. Launched in 1976, it was designed to be software-compatible with the Intel 8080, offering a compelling altern ...
, but also in the instruction set of modern
x86
x86 (also known as 80x86 or the 8086 family) is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel, based on the 8086 microprocessor and its 8-bit-external-bus variant, the 8088. Th ...
processors (although the instruction encodings are different).
Features
The 8008 architecture includes the following features:
* Seven 8-bit "scratchpad" registers: The main accumulator (A) and six other registers (B, C, D, E, H, and L).
* 14-bit program counter (PC).
* Seven-level push-down address
call stack
In computer science, a call stack is a Stack (abstract data type), stack data structure that stores information about the active subroutines and block (programming), inline blocks of a computer program. This type of stack is also known as an exe ...
. Eight registers are actually used, with the top-most register being the PC.
* Four condition code status flags: carry (C), even parity (P), zero (Z), and sign (S).
* Indirect memory access using the H and L registers (HL) as a 14-bit data pointer (the upper two bits are ignored).
Instruction set
Instructions are all one to three bytes long, consisting of an initial opcode byte, followed by up to two bytes of operands which can be an immediate operand or a program address. Instructions operate on 8-bits only; there are no 16-bit operations. There is only one mechanism to address data memory: indirect addressing pointed to by a concatenation of the H and L registers, referenced as M. The 8008 does, however, support 14-bit program addresses. It has automatic CAL and RET instructions for multi-level subroutine calls and returns which can be conditionally executed, like jumps. Eight one-byte call instructions (RST) for subroutines exist at the fixed addresses 00h, 08h, 10h, ..., 38h. These are intended to be supplied by external hardware in order to invoke interrupt service routines, but can employed as fast calls. Direct copying may be made between any two registers or a register and memory. Eight math/logic functions are supported between the accumulator (A) and any register, memory, or an immediate value. Results are always deposited in A. Increments and decrements are supported for most registers but, curiously, not A. Register A does, however, support four different rotate instructions. All instructions are executed in 3 to 11 states. Each state requires two clocks.
Code example 1

The following 8008
assembly source code is for a subroutine named
MEMCPY
that copies a block of data bytes of a given size from one location to another. Intel's 8008 assembler supported only + and - operators. This example borrows the 8080's assembler AND and SHR (shift right) operators to select the low and high bytes of a 14-bit address for placement into the 8 bit registers. A contemporaneous 8008 programmer was expected to calculate the numbers and type them in for the assembler.
In the code above, all values are given in octal. Locations , , and are 16-bit parameters for the subroutine named . In actuality, only 14 bits of the values are used, since the CPU has only a 14-bit addressable memory space. The values are stored in
little-endian
'' Jonathan_Swift.html" ;"title="Gulliver's Travels'' by Jonathan Swift">Gulliver's Travels'' by Jonathan Swift, the novel from which the term was coined
In computing, endianness is the order in which bytes within a word (data type), word of d ...
format, although this is an arbitrary choice, since the CPU is incapable of reading or writing more than a single byte into memory at a time. Since there is no instruction to load a register directly from a given memory address, the HL register pair must first be loaded with the address, and the target register can then be loaded from the M operand, which is an indirect load from the memory location in the HL register pair. The BC register pair is loaded with the parameter value and decremented at the end of the loop until it becomes zero. Note that most of the instructions used occupy a single 8-bit opcode.
Code example 2
The following 8008 assembly source code is for a simplified subroutine named MEMCPY2 that copies a block of data bytes from one location to another. By reducing the byte counter to 8 bits, there is enough room to load all the subroutine parameters into the 8008's register file.
Interrupts
Interrupts on the 8008 are only partially implemented. After the INT line is asserted, the 8008 acknowledges the interrupt by outputting a state code of S0,S1,S2 = 011 at T1I time. At the subsequent instruction fetch cycle, an instruction is "jammed" (Intel's word) by external hardware on the bus. Typically this is a one-byte RST instruction.
At this point, there is a problem. The 8008 has no provision to save its
architectural state. The 8008 can only write to memory via an address in the HL register pair. When interrupted, there is no mechanism to save HL so there is no way to save the other registers and flags via HL. Because of this, some sort of external memory device such as a hardware
stack
Stack may refer to:
Places
* Stack Island, an island game reserve in Bass Strait, south-eastern Australia, in Tasmania’s Hunter Island Group
* Blue Stack Mountains, in Co. Donegal, Ireland
People
* Stack (surname) (including a list of people ...
or a pair of read/write
registers must be attached to the 8008 via the I/O ports to help save the state of the 8008.
Designers
*CTC (''Instruction set and architecture''):
Victor Poor
Victor "Vic" Poor (July 12, 1933 – August 17, 2012) was an American engineer and computer pioneer. At Computer Terminal Corporation (later renamed Datapoint Corporation), he co-created the architecture that was ultimately implemented in th ...
and
Harry Pyle.
*Intel (''Implementation in silicon''):
**
Ted Hoff and
Stan Mazor proposed a single-chip implementation of the CTC architecture, using RAM-register memory rather than shift-register memory, and also added a few instructions and interrupt facility. The 8008 (originally called 1201) chip design started before the 4004 development. Hoff and Mazor, however, could not and did not develop a "silicon design" because they were neither chip designers nor process developers, and furthermore the necessary
bootstrap load silicon-gate-based design methodology and circuits, under development by Federico Faggin for the 4004, were not yet available.
**
Federico Faggin
Federico Faggin (, ; born 1 December 1941) is an Italian-American physicist, engineer, inventor and entrepreneur. He is best known for designing the first commercial microprocessor, the Intel 4004. He led the 4004 (MCS-4) project and the desig ...
, having finished the design of the 4004, became leader of the project from January 1971 until its successful completion in April 1972, after it had been suspended – for lack of progress – for about seven months.
**
Hal Feeney, project engineer, did the detailed logic design, circuit design, and physical layout under Faggin's supervision, employing the same design methodology that Faggin had originally developed for the Intel 4004 microprocessor, and utilizing the basic circuits he had developed for the 4004. A combined "HF" logo was etched onto the chip about halfway between the D5 and D6 bonding pads.
Second sources
second source
In the electronics industry, a second source is a company that is licensed to manufacture and sell components originally designed by another company (the first source).
It is common for engineers and purchasers to seek components that are availab ...
, the first programming language targeting a microprocessor, the Intel 8008, developed by