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4-bit computing
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<h2 id="history">History</h2> <p>A 4-bit processor may seem limited, but it is a good match for calculators, where each decimal digit fits into four bits.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> </p><p>Some of the first <a href="/facts/Microprocessor/Fx9CaQht">microprocessors</a> had a 4-bit word length and were developed around 1970. The first commercial microprocessor was the <a href="/facts/Binary-coded_decimal/dWTaE7ES">binary-coded decimal</a> (BCD-based) <a href="/facts/Intel_4004/kAoetjSU">Intel 4004</a>,<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a><a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> 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 <a href="/facts/Intel_4040/Ah4zPtUY">Intel 4040</a>, which added <a href="/facts/Interrupt/Mm6C4rpc">interrupt</a> support and a variety of other new features. </p><p>The first commercial single-chip computer was the 4-bit <a href="/facts/Texas_Instruments/88NUhuHF">Texas Instruments</a> <a href="/facts/TMS_1000/WSCWb9LG">TMS 1000</a> (1974).<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> It contained a 4-bit <a href="/facts/Central_processing_unit/Jxp1bqMV">CPU</a> with a <a href="/facts/Harvard_architecture/n9YMly7Q">Harvard architecture</a> and 8-bit-wide instructions, an on-chip instruction ROM, and an on-chip data RAM with 4-bit words.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> </p><p>The <a href="/facts/Rockwell_PPS-4/6d4BPsIy">Rockwell PPS-4</a> 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.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p><p>The 4-bit processors were programmed in <a href="/facts/Assembly_language/7XuV0cla">assembly language</a> or <a href="/facts/Forth_(programming_language)/mYtWVNhF">Forth</a>, e.g. "MARC4 Family of 4 bit Forth CPU"<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> (which is now discontinued) because of the extreme size constraint on programs and because common programming languages (for <a href="/facts/Microcontroller/MKrnAhnm">microcontrollers</a>, 8-bit and larger), such as the <a href="/facts/C_(programming_language)/Ky2No763">C programming language</a>, do not support 4-bit data types (C, and <a href="/facts/C%252B%252B/Et0F2qn9">C++</a>, and more languages require that the size of the <a href="/facts/Character_(computing)/X2zKLFFB">char</a> data type be at least 8 bits,<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> and that all data types other than bitfields have a size that is a multiple of the character size<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a><a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a><a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a>). </p><p>The 1970s saw the emergence of 4-bit software applications for mass markets like pocket calculators. During the 1980s, 4-bit microprocessors were used in <a href="/facts/Handheld_electronic_game/LTnxWIhf">handheld electronic games</a> to keep costs low. </p><p>In the 1970s and 1980s, a number of research and commercial computers used <a href="/facts/Bit_slicing/lf0t4CB3">bit slicing</a>, in which the CPU's <a href="/facts/Arithmetic_logic_unit/SgIjPzSc">arithmetic logic unit</a> (ALU) was built from multiple 4-bit-wide sections, each section including a chip such as an <a href="/facts/AMD_Am2900/zTN3yqdm">Am2901</a> or <a href="/facts/74181/y2F9zgPS">74181</a>. </p><p>The <a href="/facts/Zilog_Z80/Jeqe2h55">Zilog Z80</a> (discontinued in 2024), although it is an 8-bit microprocessor, has a 4-bit ALU.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a><a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> </p><p>Although the <a href="/facts/Data_General_Nova/z4YhpLuD">Data General Nova</a> is a series of 16-bit minicomputers, the original Nova and the Nova 1200 internally processed numbers 4 bits at a time with a 4-bit ALU,<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> sometimes called "nybble-serial".<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> </p><p>The <a href="/facts/HP_Saturn/jHVxcXpF">HP Saturn</a> processors, used in many <a href="/facts/Hewlett-Packard/abuNSYNu">Hewlett-Packard</a> calculators between 1984 and 2003 (including the <a href="/facts/HP_48_series/FonQov9J">HP 48 series</a> of scientific calculators) are "4-bit" (or hybrid 64-/4-bit) machines; as the Intel 4004 did, they string multiple 4-bit words together, e.g. to form a 20-bit memory address, and most of the registers are 64 bits wide, storing 16 4-bit digits.<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a><a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a><a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a> </p><p>In addition, some early calculators – such as the 1967 Casio AL-1000, the 1972 <a href="/facts/Sinclair_Executive/lKJn272n">Sinclair Executive</a>, and the aforementioned 1984 <a href="/facts/HP_Saturn/jHVxcXpF">HP Saturn</a> – had 4-bit <a href="/facts/Datapath/wNDBaIfU">datapaths</a> that accessed their registers 4 bits (one BCD digit) at a time.<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a> </p> <h2 id="uses">Uses</h2> <p>One bicycle computer specifies that it uses a "4 bit, 1-chip microcomputer".<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a> Other typical uses include <a href="/facts/Coffeemaker/8PwCovmD">coffee makers</a>, <a href="/facts/Remote_control/A9zmkgIV">infrared remote controls</a>,<a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a> and <a href="/facts/Security_alarm/btzrpRr9">security alarms</a>.<a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a> </p><p>The processor in Barbie typewriters that can encrypt is a 4-bit microcontroller.<a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a> </p><p>Several manufacturers used 4-bit microcontrollers in their early electronic games:<a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a> </p> <ul><li><a href="/facts/Mattel/WM3blRN4">Mattel's</a> Funtronics Jacks, Red Light Green Light, Tag, Plus One and Dalla$.</li> <li><a href="/facts/Milton_Bradley_Company/ws51eMfQ">Milton Bradley</a> Lightfight and Electronic Battleship 1982.</li> <li><a href="/facts/Coleco/e0PekMbB">Coleco</a> Head to Head Basketball.</li> <li>National Semiconductor Quiz Kid Racer.</li> <li><a href="/facts/Entex_Industries/3ByTnJuz">Entex</a> Space Invader.</li> <li><a href="/facts/Texas_Instruments/88NUhuHF">Texas Instruments</a> My Little Computer.<a class="footnote-ref" id="fnref:26" href="#fn:26"><sup>26</sup></a></li></ul> <p>Western Digital used a 4-bit microcontroller as the basis for their WD2412 time-of-day clock.<a class="footnote-ref" id="fnref:27" href="#fn:27"><sup>27</sup></a> </p><p>The <a href="/facts/Grundy_Newbrain/V4b0hI57">Grundy Newbrain</a> computer uses a 4-bit microcontroller to manage its keyboard, tape I/O, and its built-in 16 character <a href="/facts/Vacuum_fluorescent_display/70BmkStl">VF</a> alphanumeric display.<a class="footnote-ref" id="fnref:28" href="#fn:28"><sup>28</sup></a> </p> <h2 id="details">Details</h2> <p class="note">Main article: <a href="/facts/Nibble/PUaqCEVw">Nibble</a></p> <p>With 4 bits, it is possible to create 16 different values. All single-digit <a href="/facts/Hexadecimal/02ohQW22">hexadecimal</a> numbers can be written with four bits. </p><p><a href="/facts/Binary-coded_decimal/dWTaE7ES">Binary-coded decimal</a> is a digital encoding method for numbers using decimal notation, with each decimal digit represented by four bits. </p> <h2 id="list-of-4-bit-processors">List of 4-bit processors</h2> <ul><li><a href="/facts/Intel_4004/kAoetjSU">Intel 4004</a> (first 4-bit microprocessor from 1971, though <a href="/facts/Four-Phase_Systems/faG3gtPc">Four-Phase Systems</a> AL1 from 1969 is older, discontinued 1981)</li> <li><a href="/facts/Intel_4040/Ah4zPtUY">Intel 4040</a> (discontinued 1981)</li> <li><a href="/facts/TMS_1000/WSCWb9LG">TMS 1000</a> (the first high-volume commercial microcontroller, from 1974, after Intel 4004; now discontinued)</li> <li><a href="/facts/Atmel/kIDF6tmA">Atmel</a> MARC4 core<a class="footnote-ref" id="fnref:29" href="#fn:29"><sup>29</sup></a><a class="footnote-ref" id="fnref:30" href="#fn:30"><sup>30</sup></a> (discontinued because of Low demand. "Last ship date: 7 March 2015"<a class="footnote-ref" id="fnref:31" href="#fn:31"><sup>31</sup></a>)</li> <li><a href="/facts/Samsung/oNXUwDjn">Samsung</a> S3C7 (KS57 Series) 4-bit microcontrollers (RAM: 512 to 5264 nibbles, 6 MHz clock)</li> <li><a href="/facts/Toshiba/QHRaw8Tr">Toshiba</a> <a href="/facts/TLCS-47/pDKs1JCB">TLCS-47</a> series</li> <li><a href="/facts/HP_Saturn/jHVxcXpF">HP Saturn</a></li> <li><a href="/facts/NEC/YnlUsMBA">NEC</a> <a href="/facts/%25CE%259CPD75X/YnlUsMBA">μPD75X</a></li> <li>NEC <a href="/facts/%25CE%259CCOM-4/zY4MjIcq">μCOM-4</a></li> <li>NEC (now <a href="/facts/Renesas/ujhb9Dcz">Renesas</a>) μPD612xA (discontinued), μPD613x, <a href="/facts/%25CE%259CPD6x/YnlUsMBA">μPD6x</a><a class="footnote-ref" id="fnref:32" href="#fn:32"><sup>32</sup></a><a class="footnote-ref" id="fnref:33" href="#fn:33"><sup>33</sup></a> and <a href="/facts/%25CE%259CPD1724x/YnlUsMBA">μPD1724x</a><a class="footnote-ref" id="fnref:34" href="#fn:34"><sup>34</sup></a> infrared remote control transmitter microcontrollers<a class="footnote-ref" id="fnref:35" href="#fn:35"><sup>35</sup></a><a class="footnote-ref" id="fnref:36" href="#fn:36"><sup>36</sup></a></li> <li><a href="/facts/EM_Microelectronic-Marin/ahlQ3aEL">EM Microelectronic-Marin</a> EM6600 family,<a class="footnote-ref" id="fnref:37" href="#fn:37"><sup>37</sup></a> EM6580,<a class="footnote-ref" id="fnref:38" href="#fn:38"><sup>38</sup></a><a class="footnote-ref" id="fnref:39" href="#fn:39"><sup>39</sup></a> EM6682,<a class="footnote-ref" id="fnref:40" href="#fn:40"><sup>40</sup></a> etc.</li> <li>Epson <a href="/facts/S1C63/mEn9Hjx3">S1C63</a> family</li> <li><a href="/facts/National_Semiconductor/xeAD8doA">National Semiconductor</a> "COPS I" and "COPS II" ("<a href="/facts/COP400/KMN2u3A2">COP400</a>") 4-bit microcontroller families<a class="footnote-ref" id="fnref:41" href="#fn:41"><sup>41</sup></a></li> <li><a href="/facts/National_Semiconductor/xeAD8doA">National Semiconductor</a> MAPS MM570X</li> <li><a href="/facts/Sharp_Electronics/IbmkAjKB">Sharp</a> SM590/SM591/SM595<a class="footnote-ref" id="fnref:42" href="#fn:42"><sup>42</sup></a>: 26–34 </li> <li>Sharp SM550/SM551/SM552<a class="footnote-ref" id="fnref:43" href="#fn:43"><sup>43</sup></a>: 36–48 </li> <li>Sharp SM578/SM579<a class="footnote-ref" id="fnref:44" href="#fn:44"><sup>44</sup></a>: 49–64 </li> <li>Sharp SM5E4<a class="footnote-ref" id="fnref:45" href="#fn:45"><sup>45</sup></a>: 65–74 </li> <li>Sharp LU5E4POP<a class="footnote-ref" id="fnref:46" href="#fn:46"><sup>46</sup></a>: 75–82 </li> <li>Sharp SM5J5/SM5J6<a class="footnote-ref" id="fnref:47" href="#fn:47"><sup>47</sup></a>: 83–99 </li> <li>Sharp SM530<a class="footnote-ref" id="fnref:48" href="#fn:48"><sup>48</sup></a>: 100–109 </li> <li>Sharp SM531<a class="footnote-ref" id="fnref:49" href="#fn:49"><sup>49</sup></a>: 110–118 </li> <li>Sharp SM500<a class="footnote-ref" id="fnref:50" href="#fn:50"><sup>50</sup></a>: 119–127 (ROM 1197×8 bit, RAM 40×4 bit, a divider and 56-segment LCD driver circuit)</li> <li>Sharp SM5K1<a class="footnote-ref" id="fnref:51" href="#fn:51"><sup>51</sup></a>: 128–140 </li> <li>Sharp SM4A<a class="footnote-ref" id="fnref:52" href="#fn:52"><sup>52</sup></a>: 141–148 </li> <li>Sharp SM510<a class="footnote-ref" id="fnref:53" href="#fn:53"><sup>53</sup></a>: 149–158 (ROM 2772×8 bit, RAM 128×4 bit, a divider and 132-segment LCD driver circuit)</li> <li>Sharp SM511/SM512<a class="footnote-ref" id="fnref:54" href="#fn:54"><sup>54</sup></a>: 159–171 (ROM 4032×8 bit, RAM 128/142×4 bit, a divider and 136/200-segment LCD driver circuit)</li> <li>Sharp SM563<a class="footnote-ref" id="fnref:55" href="#fn:55"><sup>55</sup></a>: 172–186 </li></ul> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/GMC-4/ANqn2c6D">GMC-4</a></li> <li><a href="/facts/Hitachi_HD44780_LCD_controller/ht1UBfXK">Hitachi HD44780 LCD controller</a></li> <li>Intel's <a href="/facts/Low_Pin_Count/5xx1mgEr">LPC</a> (low-pin-count) bus/interface for 4-bit communication <ul><li>Its successor for modern computers, Intel's <a href="/facts/Enhanced_Serial_Peripheral_Interface/uSCU56eG">Enhanced Serial Peripheral Interface</a> (eSPI), allows 1-bit, 2-bit, and 4-bit communication</li></ul></li></ul> <h2 id="external-links">External links</h2> <ul><li><a href="http://www.hpmuseum.org/saturn.htm">Saturn CPU</a></li> <li><a href="https://web.archive.org/web/20130729191831/http://www.epson.jp/device/semicon_e/product/mcu/high_4bit/">"Products: High Performance 4-bit Microcontrollers (S1C63 family)"</a>. <i>Epson</i>. Archived from <a href="http://www.epson.jp/device/semicon_e/product/mcu/high_4bit/">the original</a> on 2013-07-29.</li> <li><a href="http://www.embeddedinsights.com/channels/2010/12/10/considerations-for-4-bit-processing/">Considerations for 4-bit processing</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Liu, Shih-Yang; Liu, Zechun; Huang, Xijie; Dong, Pingcheng; Cheng, Kwang-Ting (2023). "LLM-FP4: 4-Bit Floating-Point Quantized Transformers". Proceedings of the 2023 Conference on Empirical Methods in Natural Language Processing. pp. 592–605. arXiv:2310.16836. doi:10.18653/v1/2023.emnlp-main.39. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Ken Shirriff. "Reverse engineering RAM storage in early Texas Instruments calculator chips". <a href="https://www.righto.com/2020/11/reverse-engineering-ram-storage-in.html" target="_blank">https://www.righto.com/2020/11/reverse-engineering-ram-storage-in.html</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Mack, Pamela E. (2005-11-30). "The Microcomputer Revolution". Retrieved 2009-12-23. <a href="http://www.clemson.edu/caah/history/FacultyPages/PamMack/lec122/micro.htm" target="_blank">http://www.clemson.edu/caah/history/FacultyPages/PamMack/lec122/micro.htm</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"History in the Computing Curriculum" (PDF). Archived from the original (PDF) on 2011-07-19. Retrieved 2017-06-22. <a href="https://web.archive.org/web/20110719211222/http://www.hofstra.edu/pdf/CompHist_9812tla6.PDF" target="_blank">https://web.archive.org/web/20110719211222/http://www.hofstra.edu/pdf/CompHist_9812tla6.PDF</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Ken Shirriff. "Reverse engineering RAM storage in early Texas Instruments calculator chips". <a href="https://www.righto.com/2020/11/reverse-engineering-ram-storage-in.html" target="_blank">https://www.righto.com/2020/11/reverse-engineering-ram-storage-in.html</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>TMS 1000 Series Data Manual (PDF). Texas Instruments. December 1976. Retrieved 2013-07-20. <a href="http://blog.kevtris.org/blogfiles/TMS_1000_Data_Manual.pdf" target="_blank">http://blog.kevtris.org/blogfiles/TMS_1000_Data_Manual.pdf</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>"Rockwell PPS-4". <a href="http://www.antiquetech.com/?page_id=796" target="_blank">http://www.antiquetech.com/?page_id=796</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>"Forth Chips". www.ultratechnology.com. <a href="http://www.ultratechnology.com/chips.htm" target="_blank">http://www.ultratechnology.com/chips.htm</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>ISO/IEC 9899:1999 specification. p. 20, § 5.2.4.2.1. Retrieved 2023-07-24. <a href="https://c0x.shape-of-code.com/5.2.4.2.1.html" target="_blank">https://c0x.shape-of-code.com/5.2.4.2.1.html</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>ISO/IEC 9899:1999 specification. p. 37, § 6.2.6.1 (4). Retrieved 2023-07-24. <a href="https://c0x.shape-of-code.com/6.2.6.1.html" target="_blank">https://c0x.shape-of-code.com/6.2.6.1.html</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Cline, Marshall. "C++ FAQ: the rules about bytes, chars, and characters". <a href="http://www.parashift.com/c++-faq-lite/bytes-review.html" target="_blank">http://www.parashift.com/c++-faq-lite/bytes-review.html</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>"4-bit integer". cplusplus.com. Retrieved 2014-11-21. <a href="http://www.cplusplus.com/forum/general/51911/" target="_blank">http://www.cplusplus.com/forum/general/51911/</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Shima, Masatoshi; Faggin, Federico; Ungermann, Ralph; Slater, Michael (2007-04-27). "Zilog Oral History Panel on the Founding of the Company and the Development of the Z80 Microprocessor" (PDF). <a href="https://archive.computerhistory.org/resources/text/Oral_History/Zilog_Z80/102658073.05.01.pdf" target="_blank">https://archive.computerhistory.org/resources/text/Oral_History/Zilog_Z80/102658073.05.01.pdf</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>Shirriff, Ken. "The Z-80 has a 4-bit ALU". <a href="http://www.righto.com/2013/09/the-z-80-has-4-bit-alu-heres-how-it.html" target="_blank">http://www.righto.com/2013/09/the-z-80-has-4-bit-alu-heres-how-it.html</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>Hendrie, Gardner (2002-11-22). "Oral History of Edson (Ed) D. de Castro" (PDF) (Interview). p. 44. <a href="http://archive.computerhistory.org/resources/access/text/2012/07/102702207-05-01-acc.pdf" target="_blank">http://archive.computerhistory.org/resources/access/text/2012/07/102702207-05-01-acc.pdf</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>"Nova 1200" <a href="https://rcsri.org/collection/nova-1200/" target="_blank">https://rcsri.org/collection/nova-1200/</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> <li id="fn:17"><p>"The Saturn Processor". Retrieved 2015-12-23. <a href="http://www.hpmuseum.org/saturn.htm" target="_blank">http://www.hpmuseum.org/saturn.htm</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></p></li> <li id="fn:18"><p>"Guide to the Saturn Processor". Retrieved 2014-01-14. <a href="http://grack.com/writings/hp48/GuidetotheSaturnProcessor.html" target="_blank">http://grack.com/writings/hp48/GuidetotheSaturnProcessor.html</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></p></li> <li id="fn:19"><p>"Introduction to Saturn Assembly Language". 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