4-bit microprocessors

In the 4-bit microprocessor or computer architecture will have a data path width or a highest operand width of 4 bits or a nibble. And also these architectures or microprocessors typically will have a matching register file with registers width of 4 bits and 4-8-bit wide addresses.

Most of the first microprocessors during the early 1970s had 4-bit word sizes. Both the Intel 4004, the first commercial microprocessor, and the 4040 had a 4-bit word length, but had 8-bit instructions. Some of the first microcontrollers such as the TMS1000 made by Texas Instruments and NEC's μPD751 also had 4-bit words. 4-bit word were proven to be very limiting and by 1974 there was a shift to larger architectures such as 8 and 12-bit architectures.

The advent of microprocessors was accidental. Intel Corporation founded by Moore and Noyce in 1968 was initially focused on creating semiconductor memory (DRAMs and EPROMs) for digital computers. A company called Busicom, a Japanese calculator manufacturer, in the year 1969, approached Intel with a design for a small calculator, which required 12 custom chips. Ted Hoff, an Intel engineer felt that a general-purpose logic device could replace the separate multiple components. This is the first idea towards the development of the first microprocessor. Microprocessors made a modest beginning as the main drivers for calculator designs.

Federico Faggin and Stanley Mazor realized Ted Hoff's ideas into hardware at Intel. And as a result we had Intel 4000 family comprising of multiple microprocessors. E.g. 4001 (2K ROM), the 4002 (320-bit RAM), the 4003 (10-bit I/O shift-register) and the 4004, a 4-bit central processing unit (CPU). In the year November 15, 1971, Intel introduced the 4004 microprocessor to the worldwide market. It was designed with 2,300 transistors and actually it was a 4-bit PMOS chip. It was not truly a general-purpose microprocessor as it was basically designed for a calculator. Almost at the same period of time, Texas Instruments also developed the 4-bit microprocessor TMS 1000. As the inventor and owner of the microprocessor patent, Texas Instruments is recognized.