Intel 4004

The Intel 4004, a 4-bit CPU, was one of the world's first microprocessors Although the 4004 is widely considered to be the "first" microprocessor, other designs such as Ray Holt's F14 CADC Microprocessor were implemented prior to the 4004.

The 4004 was released in 16-pin ceramic DIP packaging on November 15th, 1971. The 4004 was the first computer processor designed and manufactured by chip maker Intel, which previously made semiconductor memory chips.

The chief designers of the chip were Ted Hoff and Federico Faggin of Intel and Masatoshi Shima of Busicom.

Originally designed for the Japanese company Busicom to be used in their line of calculators, the 4004 was also provided with a family of custom support chips (e.g., 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.

Technical specifications

• Clock speed is 108 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, not to be placed in the same memory as
  •   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

Custom 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 & I/O access converter to standard memory and I/O chips

Note: a 4001 chip cannot be used in a system along with a 4008/4009 pair.

Collectability

The Intel 4004, is one of world's most sought-after collectable / antique chips. Of highest value are 4004's that are gold and white, with visible so called 'grey traces' on the white portion. As of 2004, such chips reached around US$400 each on eBay. The slightly less valuable white and gold chips without grey traces typically reach $200 to $300. Those chips without a 'date code' underneath are earlier versions, and therefore worth slightly more. Other valuable chips include the Intel 4040.

External links

• Federico Faggin's Intel 4004 design history web site
• Interview with Masatoshi Shima of Busicom regarding his role in the 4004
• Comprehensive 'online CPU museum', also covers memory chips
• A good reference on old CPUs and collecting them
• A description of Ray Holt's F14 CADC microprocessor