Intel 4004

Intel 4004

The Intel 4004 is a 4-bit central processing unit (CPU) released by Intel Corporation in 1971. Most people agree that the 4004 is the first complete CPU on one chip, the first microprocessor. A feat made possible by the use of the new silicon gate technology allowing the integration of a higher number of transistors and a faster speed than was possible before. The 4004 employed a 10 μm silicon-gate enhancement load PMOS technology and could execute approximately 92,000 instructions per second (that is, a singular instruction was executed in 11 microseconds).

History and description

The 4004 was released in 16-pin CERDIP packaging on November 15 1971. The 4004 is the first computer processor designed and manufactured by chip maker Intel, which previously made semiconductor memory chips. The chief designers of the chip were Federico Faggin (project leader and chip designer - developed the new random logic methodology with silicon gate and several technological and circuit innovations that made it possible to fit the microprocessor in one chip in 1970-1971) and Ted Hoff (formulated the architectural proposal in 1969) of Intel, and Masatoshi Shima of Busicom (later of ZiLOG, founded by Federico Faggin at the end of 1974, the first company entirely devoted to microprocessors). Shima designed the Busicom calculator firmware and assisted Faggin during the first six months of the implementation. The manager of Intel's MOS Design Department was Leslie L. Vadász. At the time of the MCS-4 development Vadasz's attention was completely focused on the mainstream business of semiconductor memories and he left the leadership and the management of the MCS-4 project to Faggin.

Originally designed for the Japanese company Busicom to be used in their line of calculators (instead of the complex special purpose calculator chipset that Busicom had designed themselves and brought to Intel to have made, which Intel determined was too complex to make with the technology they had at the time), the 4004 was also provided with a family of custom support chips. For instance, each "Program ROM" internally latched for its own use the 4004's 12-bit program address, which allowed 4 KB memory access from the 4-bit address bus if all 16 ROMs were installed. The 4004 circuit was built of 2,300 transistors, and was followed the next year by the first ever 8-bit microprocessor, the 3,300 transistor 8008 (and the 4040, a revised 4004).

As its fourth entry in the microprocessor market, Intel released the CPU that started the microcomputer revolution — the 8080.

The Intel 4004 is said to have the computing power of the ENIAC, a 1946 supercomputer that weighed 27 tons and occupied 680 square feet (63 m2) of floor space.

A popular myth has it that Pioneer 10, the first spacecraft to leave the solar system, used an Intel 4004 microprocessor. However, according to Dr. Larry Lasher of Ames Research Center, the Pioneer team did evaluate the 4004, but "it was too new at the time to include in any of the Pioneer projects." The myth was repeated by Federico Faggin himself in a lecture for the Computer History Museum in 2006.

On 15 November 2006, the 35th anniversary of the Intel 4004, Intel celebrated by releasing the chip's schematics, mask works, and user manual.

The 4004 and the MCS-4 family

The 4004 is a complete CPU (central processing unit) integrated in a single chip, making the 4004 the world's first microprocessor. Before the microprocessor, CPUs were built with many chips or with a few LSI (large scale integration) chips. The CPUs built with a few LSI chips were steps toward the microprocessor but were not microprocessors. The 4004 is part of a family of four LSI components - the MCS-4 family - that can be used to build digital computers with varying amounts of memory. The other components of the MCS-4 family are memories and input/output circuits, which are not considered part of a CPU in any computer classification, but are necessary to implement a complete computer. Specifically:

  • the 4001 is a ROM (read-only memory) with 4 lines of I/O (input/output)
  • the 4002 is a RAM (random access memory) with 4 lines of output
  • the 4003 is a static shift register to be used for expanding the I/O lines, for example, for keyboard scanning or for controlling a printer

The functional elements integrated in the 4004 are:

  • 16 general purpose registers
  • program counter and three levels of return address stack
  • ALU both binary and decimal
  • instruction decoder and all the control logic for the internal functional blocks of the CPU
  • generation of timing signal for the CPU and for the rest of the MCS-4 family
  • control of the external bus for the memory and for the I/O functions.

The 4004 included also the control functions for the memory and the I/O which are not normally handled by the microprocessor. The 4004, therefore, is not only a complete CPU, but has also additional functionality that normally is not considered a part of a CPU. The first commercial product to use a microprocessor was the Busicom calculator 141-PF.

First microprocessor commercially available and sold as a component set

According to Nick Tredennick, a recognized engineer and microprocessor designer, and an expert witness to the Boone/Hyatt patent case:

Technical specifications

  • Maximum clock speed is 740 kHz
  • Separate program and data storage (i.e., a Harvard architecture). Contrary to most Harvard architecture designs, however, which use separate buses, the 4004, with its need to keep pin count down, uses a single multiplexed 4-bit bus for transferring:
    • 12-bit addresses
    • 8-bit instructions
    • 4-bit data words
  • Instruction set contains 46 instructions (of which 41 are 8 bits wide and 5 are 16 bits wide)
  • Register set contains 16 registers of 4 bits each
  • Internal subroutine stack is 3 levels deep.

Microarchitecture and pinout

Click the pictures to view the full-size versions.

Support chips

  • 4001: 256-byte ROM (256 8-bit program instructions), and one built-in 4-bit I/O port
  • 4002: 40-byte RAM (80 4-bit data words), and one built-in 4-bit output port; the RAM portion of the chip is organized into four "registers" of twenty 4-bit words:
    • 16 data words (used for mantissa digits in the original calculator design)
    • 4 status words (used for exponent digits and signs in the original calculator design)
  • 4003: 10-bit parallel output shift register for scanning keyboards, displays, printers, etc.
  • 4008: 8-bit address latch for access to standard memory chips, and one built-in 4-bit chip select and I/O port
  • 4009: program and I/O access converter to standard memory and I/O chips
  • 4269: keyboard/display interface
  • 4289: memory interface (combines functions of 4008 and 4009)

Naming the first microprocessor

When Federico Faggin designed the MCS-4 family he also christened the chips with distinct names: 4001, 4002, 4003, and 4004, breaking away from the numbering scheme used by Intel at that time which would have required the names 1302, 1105, 1507, and 1202 respectively. Had he followed Intel's number sequence, the idea that the chips were part of a family of components intended to work seamlessly together would have been lost.

Intel's early numbering scheme for integrated circuits contemplated using a four-digit number for each component. The most significant digit position indicated the process technology used, as follows: The number "1" meant P-channel MOS, "2" indicated N-channel MOS, "3" was reserved for bipolar technology, and "5" was used for CMOS technology. No other numbers were used.

The next most significant digit was used to indicate the generic function performed by the component, as follows: "1" was used for RAM, "2" indicated random logic, "3" indicated ROM, "5" meant shift register, "6" and "7" were used for one-time programmable ROM and EPROM respectively. The last two digits of the number were used to indicate the sequential number in the development of the component.


The Intel 4004 is one of the world's most sought-after collectible/antique chips. Of highest value are 4004s that are gold and white, with so-called 'grey traces' visible on the white ceramic (the original package type). As of 2005, such chips have reached around US$1000 each on eBay. The slightly less valuable white and gold chips without grey traces typically reach $300 to $500. Those chips without a 'date code' underneath are earlier versions, and therefore worth slightly more. More recently however, these vintage ICs have been dropping in value due to their relative abundance as the market is now flooded with surplus stock from sellers looking to cash in on the Intel craze.

Original publications

  • F. Faggin and M.E. Hoff: "Standard parts and custom design merge in four-chip processor kit". Electronics/April 24, 1972, pp. 112-116
  • F. Faggin, M.Shima, M.E. Hoff, Jr., H. Feeney, S. Mazor: "The MCS-4 An LSI micro computer system". IEEE '72 Region Six Conference

Patents on 4004

  • US Patent 3,753,011 August 14, 1973. Faggin, Federico: Power supply settable bi-stable circuit.
  • US Patent 3,821,715 June 28, 1974. Hoff, Marcian; Mazor, Stanley; Faggin, Federico: Memory system for multi-chip digital computer.


  • Federico Faggin, Marcian E. Hoff Jr., Stanley Mazor and Masatoshi Shima. The history of the 4004. IEEE Micro, 16(6):10-20, December 1996. "The 4004 design team tells its story."
  • Live recording of presentations by Ted Hoff and Federico Faggin at the Computer History Museum for the 35th anniversary of the first microprocessor, available also on You Tube (


External links

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