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The first widely adopted 8-bit [[microprocessor]] was the [[Intel 8080]], being used in many hobbyist computers of the late 1970s and early 1980s, often running the [[CP/M]] [[operating system]]; it had 8-bit data words and 16-bit addresses. The [[Zilog Z80]] (compatible with the 8080) and the [[Motorola 6800]] were also used in similar computers. The Z80 and the [[MOS Technology 6502]] 8-bit CPUs were widely used in [[home computer]]s and [[Second generation of video game consoles|second-]] and [[Third generation of video game consoles|third-generation game consoles]] of the 1970s and 1980s. Many 8-bit CPUs or [[microcontroller]]s are the basis of today's ubiquitous [[embedded systems]].
== Historical context ==
8-bit microprocessors were the first widely used microprocessors in the computing industry, marking a major shift from mainframes and minicomputers to smaller, more affordable systems. The introduction of 8-bit processors in the 1970s enabled the production of personal computers, leading to the popularization of computing and setting the foundation for the modern computing landscape.
The 1976 [[Zilog Z80]], one of the most popular 8-bit CPUs (though with [[4-bit computing|4-bit]] ALU, at least in the original), was discontinued in 2024 (its product line Z84C00), with Last Time Buy (LTB) orders by June 14, 2024.<ref>{{Cite web |date=15 April 2024 |title=X80 Product line: Z84C00 |url=https://www.mouser.com/PCN/Littelfuse_PCN_Z84C00.pdf}}</ref>
== Details ==
<!-- ==Range for storing integers== -->
An 8-bit register can store 2<sup>8</sup> different values. The [[range (computer programming)|range]] of [[integer]] values that can be stored in 8 bits depends on the [[Integer (computer science)#Value and representation|integer representation]] used. With the two most common representations, the range is 0 through 255 {{nowrap|(2<sup>8</sup> − 1)}} for representation as an ([[signedness|unsigned]]) [[binary number]], and −128 {{nowrap|(−1 × 2<sup>7</sup>)}} through 127 {{nowrap|(2<sup>7</sup> − 1)}} for representation as [[two's complement]].
8-bit CPUs use an [[octet (computing)|8-bit]] [[Bus (computing)|data bus]] and can therefore access 8 bits of data in a single [[Instruction (computer science)|machine instruction]]. The address bus is typically a double octet ([[16-bit computing|16 bit]]s) wide, due to practical and economical considerations. This implies a direct [[address space]] of 64 [[kilobyte|KB]] (65,536 bytes) on most 8-bit processors.
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While in general 8-bit CPUs have 16-bit addressing, in some architectures you have both, such as in the [[MOS Technology]] [[MOS Technology 6502|6502]] CPU, where the [[zero page]] is used extensively, saving one byte in the instructions accessing that page, and also having 16-bit addressing instructions that take 2 bytes for the address plus 1 for the opcode. Commonly [[index register]]s are 8-bit (while other "8-bit" CPUs, such as [[Motorola 6800]] had 16-bit index registers), such as the 6502 CPU, and then the size of the arrays addressed using [[indexed addressing]] instructions are at most 256 bytes, without needing longer code, i.e. meaning 8-bit addressing to each individual array.
== Notable 8-bit CPUs ==
{{Main|Microprocessor chronology}}
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== Use for training, prototyping, and general hardware education ==
8-bit processors continue to be designed today for general education about computer hardware, as well as for hobbyists' interests. One such CPU was designed and implemented using [[7400-series integrated circuits]] on a [[breadboard]].<ref>{{cite web|first=Daniel|last=Oberhaus|title= This Guy Designed and Built an 8-bit CPU from Scratch|website=[[Motherboard (website)|Motherboard]]|date=February 9, 2019|url=https://www.vice.com/en/article/a34ege/diy-8-bit-cpu|access-date=November 4, 2021}}</ref><ref>{{cite AV media|url=https://www.youtube.com/watch?v=g_ZaioqF1B0|title=Homebuilt 8-bit CPU + Computer with graphics and sound made from scratch using 74HC Logic|first=Paulo|last=Constantino}}</ref> Designing 8-bit CPU's and their respective assemblers is a common training exercise for engineering students, engineers, and hobbyists. [[FPGA]]'s are used for this purpose.
== See also ==
* [[Kenbak-1]]
== References ==
{{Reflist}}
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