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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]].
The first commercial single-chip computer was the 4-bit TMS1000 (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> The [[Texas Instruments]] [[TMS 1000]] (1974) was a 4-bit [[central processing unit|CPU]]; it had a [[Harvard architecture]], with an on-chip instruction ROM, 8-bit-wide instructions and an on-chip data RAM with 4-bit words.<ref name="TI_1976_TMS1000" />▼
▲The [[Texas Instruments]] [[TMS 1000]] (1974) was a 4-bit [[central processing unit|CPU]]; it had a [[Harvard architecture]], with an on-chip instruction ROM, 8-bit-wide instructions and an on-chip data RAM with 4-bit words.<ref name="TI_1976_TMS1000" />
The [[Rockwell PPS-4]] was another early 4-bit processor, introduced in 1972, which had a long lifetime in handheld games and similar roles. It was steadily improved and by 1975 been combined with several support chips to make a one-chip computer.<ref>{{cite web |url=http://www.antiquetech.com/?page_id=796 |title=Rockwell PPS-4}}</ref>
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