Intel 4004

The Intel 4004 (i4004), a 4-bit CPU, was the first microprocessor on a single chip, as well as the first commercially available. At about the same time, some other integrated circuit CPU designs, such as the 1970s military F14 CADC, were implemented as chipsets, ie constellations of multiple chips.

History and description

The 4004 was released in a 16-pin CERDIP package on November 15, 1971. The 4004 was the first computer processor designed and manufactured by chipmaker Intel, who previously made memory chip semiconductors. Marcian "Ted" Hoff formulated the architectural proposal in 1969. However, implementation of the microprocessor only began in 1970 when Federico Faggin was hired by Intel, from Fairchild Semiconductor, to lead the project and to design the 4004 (1970-1971). At Fairchild, Faggin had developed the pioneering technology called Silicon Gate Technology (SGT) and had also designed the first MOS integrated circuit using SGT technology (the Fairchild 3708), in 1968, demonstrating the feasibility of the new technology. As soon as he started working for Intel, Faggin created a new methodology of & # 34;random logic design & # 34; with a silicon gate, which did not exist previously, and which was used to embed the microprocessor on a single chip. His methodology was used in all of Intel's early microprocessor designs (8008, 4040, 8080). Busicom's Masatoshi Shima assisted Faggin during the development of the 4004 family and later wrote the software for the Busicom calculator. Shima joined the ZiLOG company, the first company dedicated solely to microprocessors, founded by Federico Faggin in late 1974, and developed the Z80 design with Faggin.

Originally designed for the Japanese company Busicom for use in their line of calculators, the 4004 was also provided with a family of support chips specially designed for it. For example, each "program ROM" internally it kept for its own use the 12 bit program address of the 4004, which allowed, if all 16 ROMs were installed, access to 4 KB of memory from the 4 bit address bus. The 4004 circuit was built with 2,300 transistors, and was followed the next year by the first 8-bit microprocessor, the 8008, which contained 3,300 transistors, and the 4040, which was a revised version of the 4004.

As a curious fact, the initials F. F. was printed in each 4004

As its fourth entry into the microprocessor market, Intel released the CPU that started the microcomputer revolution, the 8080, used in the Altair 8800.

Technical specifications

• 4-bit microprocessor
• Contains 2300 transistors
• 16 pin CERDIP encapsulate
• Maximum clock speed 740 kHz
• Use Harvard Architecture, that is, separate storage of programs and data. Contrary to most Harvard architecture designs, which use separate buses, 4004, with their need to keep down the pin account, used a 4-bit multiplex bus to transfer:
  • 12 bits of addresses (directing up to 4 KB)
  • 8-bit wide instructions, which should not be placed in the same 4-bit data memory wide.
• The set of instructions consists of 46 instructions (of which 41 are 8-bit wide and 5 of 16-bit wide).
• 16 4-bit records each.
• Inner stack of calls to subroutines of three depth levels.
• Chipset (auxiliary circuits) to create systems based on 4004.

Microarchitecture and pinout

Click on the images to see a full-size version.

Intel 4004 architectural block diagram.

Intel 4004 DIP chip pinout

Support chips (chipset)

• 4001: ROM 256 bytes (256 program instructions 8bits), and a built-in 4-bit I/O port*
• 4002: RAM of 40 bytes (80 4-bit data words), and a built-in 4-bit output port. The portion of RAM of the chip is organized in four "registers" of twenty words of 4 bits:
  • 16 data words (used for significant digits in the original design of the calculator)
  • 4 state words (used for exponent digits in the original calculator design)
• 4003: shift register (displacement route) of 10-bit parallel output to explore keyboards, screens, printers, etc.
• 4008: 8-bit steering lotch for access to standard memory chips, and a built-in 4-bit selection chip and I/O port*
• 4009: I/O access program and converter to standard memory and I/O chips*

(*) Note: A 4001 ROM + I/O chip cannot be used in a system together with a 4008/4009 pair.

Original posts

• 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
• 4004 design with signature The Intel 4004 is signed with the initial F.F. of its designer Federico Faggin. The signature of the CPU was a spontaneous gesture of pride for its achievements and it was also an original idea imitated, after it, by many Intel designers.
• US Patent 3,753,001 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.

Applications

The design of the i4004 was very effective for use in calculators and control devices. There are even a few old traffic light control systems in use built with the i4004.

Collectible item

The Intel 4004, naturally, is one of the old chips that can be seen in historical computer/electronics museums along with other classic chips like the 8008, 8080, 8088/8086, Motorola 6800, or the mythical Z80, as well as with memories of magnetic cores, transistors, equipment with perforated cards and others.