Editing Zilog Z80 (section)

=== Success in the market ===
The Z80 took over from the 8080 and its offspring, the [[Intel 8085|8085]], in the processor market<ref>{{Cite web |last=Adrian |first=Andre |date=June 4, 2011 |title=Z80, the 8-bit Number Cruncher |url=http://www.andreadrian.de/oldcpu/Z80_number_cruncher.html |url-status=live |archive-url=https://web.archive.org/web/20231126092639/http://www.andreadrian.de/oldcpu/Z80_number_cruncher.html |archive-date=November 26, 2023}}</ref> and became one of the most popular and widely used 8-bit CPUs.<ref name="Balch 2003"/><ref name="Seybold 1983" /> Some organizations such as [[BT Group|British Telecom]] remained loyal to the 8085 for embedded applications, owing to their familiarity with it and to its on-chip serial interface and interrupt architecture. Likewise, [[Zenith Data Systems]] paired the 8085 with the 16-bit [[Intel 8088]] in its first MS-DOS computer, the [[Zenith Z-100]], despite having previous experience with its pioneering Z80-based [[Zenith Z-89|Heathkit&nbsp;H89 and Zenith&nbsp;Z-89]] products. However, other computers were made integrating the Z80 with other CPUs: the Radio Shack [[TRS-80 Model II#Model 16|TRS-80 Model&nbsp;16]] with a [[Motorola 68000]], the [[Rainbow 100|DEC Rainbow]] with an 8088, and the [[Commodore 128]] with a [[MOS Technology 8502]].

Zilog was later producing a low-power Z80 suitable for the growing laptop computer market of the early 1980s. Intel produced a CMOS 8085 (80C85) used in battery-powered portable computers, such as the [[Kyocera]]-designed laptop from April 1983, also sold by Tandy (as [[TRS-80 Model 100]]), Olivetti, and NEC. In following years, however, CMOS versions of the Z80 (from both Zilog and Japanese manufacturers) would dominate this market as well, in products such as the [[Amstrad NC100]], [[Cambridge Z88]] and Tandy's own WP-2.

Perhaps a key to the initial success of the Z80 was the built-in DRAM refresh, at least in markets such as [[CP/M]] and other office and home computers. (Most Z80 [[embedded system]]s use [[Static random-access memory|static RAM]] that do not need refresh.) It may also have been its minimalistic two-level interrupt system, or conversely, its general multi-level daisy-chain interrupt system useful in servicing multiple Z80 IO chips. These features allowed systems to be built with less support hardware and simpler circuit board layouts.

However, others claim that its popularity was due to the duplicated registers that allowed fast context switches or more efficient processing of things like floating-point math compared to 8-bit CPUs with fewer registers. (The Z80 can keep several such numbers internally, using HL'HL, DE'DE and BC'BC as 32-bits registers, avoiding having to access them from slower RAM during computation.)<ref>{{Cite web |last=Adrian |first=Andre |date=June 4, 2011 |title=Z80, the 8-bit Number Cruncher: Z80 32-bit (long) add |url=http://www.andreadrian.de/oldcpu/Z80_number_cruncher.html#mozTocId228550 |url-status=live |archive-url=https://web.archive.org/web/20231126092639/http://www.andreadrian.de/oldcpu/Z80_number_cruncher.html#mozTocId228550 |archive-date=November 26, 2023}}</ref>

For the original [[NMOS logic|NMOS]] design, the specified upper clock-frequency limit increased successively from the introductory 2.5&nbsp;[[Hertz#SI multiples|MHz]], via the well known 4&nbsp;MHz (Z80A), up to 6&nbsp;MHz (Z80B) and 8&nbsp;MHz (Z80H).<ref>{{Cite book |title=Popular Computing |date=1983 |publisher=[[McGraw Hill Education|McGraw-Hill]] |page=15}}</ref><ref>{{Cite magazine |last=Markoff |first=John |date=October 18, 1982 |title=Zilog's speedy Z80 soups up 8-bit to 16-bit performance |url=https://books.google.com/books?id=CjAEAAAAMBAJ&pg=PA1 |url-status=live |archive-url=https://web.archive.org/web/20240105083032/https://books.google.dk/books?id=CjAEAAAAMBAJ&pg=PA1 |archive-date=January 5, 2024 |magazine=[[InfoWorld]] |publisher=Popular Computing, Inc. |location=Palo Alto, CA |page=1 |volume=4 |issue=41 |issn=0199-6649}}</ref> An NMOS version was produced as a 10&nbsp;MHz part beginning in the late 1980s. [[CMOS]] versions were developed with specified upper frequency limits ranging from 4&nbsp;MHz up to 20&nbsp;MHz for the version sold today. The CMOS versions allowed low-power standby with internal state retained, having no ''lower'' frequency limit.{{efn|Unlike the original nMOS version, which used dynamic latches and could not be stopped for more than a few thousand clock cycles.}} The fully compatible derivatives [[Hitachi HD64180|HD64180]]/[[Zilog Z180|Z180]]<ref>{{Cite book |title=Electronic design |date=1988 |publisher=Hayden |page=142 |quote=In addition to supporting the entire Z80 instruction set, the Z180}}</ref><ref>{{Cite web |last=Ganssle |first=Jack G. |date=1992 |title=The Z80 Lives! |url=http://www.z80.info/z80lives.htm |url-status=live |archive-url=https://web.archive.org/web/20231220144616/http://www.z80.info/z80lives.htm |archive-date=December 20, 2023 |quote=The designers picked an architecture compatible with the Z80, giving Z80 users a completely software compatible upgrade path. The 64180 processor runs every Z80 instruction exactly as a Z80 does}}</ref> and [[Zilog eZ80|eZ80]] are currently specified for up to 33&nbsp;MHz and 50&nbsp;MHz, respectively.