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Obsolete (in CPUs, i.e. as word-size or main datatype). Except in AI, then the future... |
Guy Harris (talk | contribs) Use {{cite conference}} for a conference paper. |
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'''4-bit computing''' is the use of [[computer architecture]]s in which [[integer (computer science)|integers]] and other [[data (computer science)|data]] units are 4 [[bit]]s wide. 4-bit [[central processing unit]] (CPU) and [[arithmetic logic unit]] (ALU) architectures are those that are based on [[processor register|registers]] or [[bus (computing)|data buses]] of that size. A group of four bits is also called a [[nibble]] and has 2<sup>4</sup> = 16 possible values, with a range of 0 to 15.
4-bit computation is obsolete, i.e. CPUs supporting 4-bit as the maximum size. However, 4-bit integers (or smaller), and 4-bit floating point is gaining ground for AI, large-language models.<ref>{{
4-bit processors were widely used in [[electronic calculator]]s and other roles where decimal math was used, like electronic [[cash register]]s, [[microwave oven]] timers, and so forth. This is because a 4-bit value holds a single [[binary-coded decimal]] (BCD) digit, making it a natural size for directly processing decimal values. As a 4-bit value is generally too small to hold a [[memory address]] for real-world programs or data, the [[address bus]] of these systems was generally larger. For instance, the canonical 4-bit [[microprocessor]], the [[Intel 4004]], had a 12-bit address format.
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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" />
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=
The 4-bit processors were programmed in [[assembly language]] or [[Forth (programming language)|Forth]], e.g. "MARC4 Family of 4 bit Forth CPU"<ref name="UT_Forth" /> (which is now discontinued) because of the extreme size constraint on programs and because common programming languages (for [[microcontroller]]s, 8-bit and larger), such as the [[C (programming language)|C programming language]], do not support 4-bit data types (C, and [[C++]], and more languages require that the size of the [[character (computing)#char|<code>char</code>]] data type be at least 8 bits,<ref name="ISOIEC9899_1999_1" /> and that all data types other than bitfields have a size that is a multiple of the character size<ref name="ISOIEC9899_1999_2" /><ref name="Cline" /><ref name="CPP" />).
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== References ==
{{
<ref name="Mack_2005">{{cite web |title=The Microcomputer Revolution |author-first=Pamela E. |author-last=Mack |date=2005-11-30 |url=http://www.clemson.edu/caah/history/FacultyPages/PamMack/lec122/micro.htm |access-date=2009-12-23}}</ref>
<ref name="Hofstra_History">{{cite web |title=History in the Computing Curriculum |url=http://www.hofstra.edu/pdf/comphist_9812tla6.pdf |access-date=2017-06-22 |archive-url=https://web.archive.org/web/20110719211222/http://www.hofstra.edu/pdf/CompHist_9812tla6.PDF |archive-date=2011-07-19 |url-status=dead}}</ref>
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{{CPU technologies}}
[[Category:Data unit]]
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