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== Usage ==
The IV/70, was introduced by [[Four-Phase Systems]] in 1971. The IV/70 has an integer word size of 24 bits. [[Byte]] addressing is not supported directly but bytes are handled by instructions that pack three bytes per word. The IV/70 CPU is a 9-chip [[Integrated_circuit#LSI|LSI]] [[microprocessor]] based on three [[Four-Phase Systems AL1|AL4]] 8-bit slice register/ALUs.<ref>[http://archive.computerhistory.org/resources/text/Four-Phase_Systems/Four-Phase.SystemIV_70.1970.102646129.pdf Brochure, System IV/70, Four Phase Systems]. From the Computer History Museum. Accessed online June 11, 2010.</ref>
The IBM [[System/360]], announced in 1964, was a popular computer system with 24-bit addressing and [[32-bit]] general registers and arithmetic. The early 1980s saw the first popular personal computers, including the [[IBM Personal Computer AT|IBM PC/AT]] with an [[Intel 80286]] processor using 24-bit addressing and [[16-bit computing|16-bit]] general registers and arithmetic, and the [[Apple Inc.|Apple]] [[Macintosh 128K]] with a [[Motorola 68000]] processor featuring 24-bit addressing and 32-bit registers. Some late-1980s Apple computers such as the [[Macintosh SE/30]] and [[Macintosh IIx]] retained some 24-bit code in their [[ROM image|ROMs]] despite being advertised as 32-bit computers. As a result, these computers require the installation of the [[MODE32]] memory manager to address more than 8Mb of RAM.<ref>{{Cite web |last=Staff |first=L. E. M. |date=1989-01-19 |title=Mac SE/30 |url=https://lowendmac.com/1989/mac-se30/ |access-date=2025-06-18 |website=Low End Mac |language=en-US}}</ref><ref>{{Cite web |last=Staff |first=L. E. M. |date=1988-09-19 |title=Mac IIx |url=https://lowendmac.com/1988/mac-iix/ |access-date=2025-06-18 |website=Low End Mac |language=en-US}}</ref>
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