Intel 4004

The Intel 4004, a 4-bit CPU, was the world's first microprocessor. It 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.

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.

Table of contents

1 Technical specifications 2 Custom support chips 3 Collectability 4 External links

Technical specifications

• 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, not to be placed in the same memory as
  •   4-bit data words
• Instruction set contains 46 instructions (41 - 8 bits wide and 5 - 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 4008/4009 chip pair.

Collectability

The Intel 4004 is probably the world's most sought-after collectable / antique chip. Of highest value are 4004's that are gold and white, with visible so called 'grey traces' on the white portion. As of January 2004, such chips reached around US$400 each on eBay. The slightly less valuable white and gold chips without grey traces typically reach $US200 to US$300. Those chips without a 'date code' on the underneath are earlier versions, and are therefore worth slightly more.

See also: List of Intel microprocessors

External links

• Comprehensive online 'CPU museum', also covers memory chips : http://www.cpu-museum.com
• Another good reference on old CPUs : http://www.antiquetech.com