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4-bit architecture
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Architecture word sizes
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The 4-bit architecture is a microprocessor or computer architecture that has a datapath width or a highest operand width of 4 bits or a nibble. These architectures typically have a matching register file with registers width of 4 bits and 4-8-bit wide addresses.

Industry

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.

In the microcontroller domain, the story is a little different. 4-bit microcontrollers found their way into many battery-powered and low power instruments and devices. Some 4-bit chips such as the Atmel MARC4 continued to be manufactured until very recently (2010s), those devices aimed directly at wireless devices such as RFID-related applications. Other 4-bit MCUs are still made to date such as the Epson's S1C60 and S1C63 MCU families. Modern 4-bit microprocessors, however, are much different to the first generation microprocessors of the 1970s - in terms of architecture, performance, and overall capabilities.

Applications

Most 4-bit microprocessors were used almost exclusively in calculators and toys, later on for various utilities, video games, controllers, and early computers. 4 bits was a logical choice for many calculators that used BDC numbers representation.

Today, 4-bit chips such as S1C60 family are still manufactured are used in many low-power devices, wireless tools, and internet of things.

4-bit microprocessors

4-bit microcontrollers

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