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A 4-bit processor may seem limited, but it is a good match for calculators, where each decimal digit fits into four bits.<ref name="Shirriff_TMS1000" />
Some of the first [[microprocessor]]s had a 4-bit word length and were developed around 1970. The first commercial microprocessor was the [[binary-coded decimal]] (BCD-based) [[Intel 4004]],<ref name="Mack_2005" /><ref name="Hofstra_History" /> developed for calculator applications in 1971; it had a 4-bit word length, but had 8-bit instructions and 12-bit addresses. It was succeeded by the [[Intel 4040]], which added [[interrupt]] support and a variety of other new features.
The first commercial single-chip computer was the 4-bit [[Texas Instruments]] [[TMS 1000]] (1974).<ref name="Shirriff_TMS1000">{{cite web |author=Ken Shirriff |url=https://www.righto.com/2020/11/reverse-engineering-ram-storage-in.html |title=Reverse engineering RAM storage in early Texas Instruments calculator chips}}</ref> It contained a 4-bit [[central processing unit|CPU]] with a [[Harvard architecture]] and 8-bit-wide instructions, an on-chip instruction ROM, and an on-chip data RAM with 4-bit words.<ref name="TI_1976_TMS1000" />
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