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A very early version of the en:Zilog Z80 — note that the date stamp is from June 1976, and the Z80 was sold from July 1976 onwards. Photographed by Gennadiy Shvets.

The idea[]

Create a create a cheep and efficient 8-bit based microprocessor chip.


The Z80 CPU is an 8-bit based microprocessor. It was introduced by Zilog in 1976 as the startup company's first product. The Z80 was conceived by Federico Faggin in late 1974 and developed by him and his then 11 employee Zilog from early 1975 until March 1976, when the first fully working samples were delivered. With the revenue from the Z80, the company could then build its own chip factories and grow to over a thousand employees over the following two years.

The Zilog Z80 was a software compatible extension and enhancement of the Intel 8080 and, like it, was mainly aimed at embedded systems. According to the designers, the primary targets for the Z80 CPU (and its optional support and peripheral ICs) were products like intelligent terminals, high end printers and advanced cash registers as well as telecom equipment, industrial robots and other kinds of automation equipment.

The Z80 was officially introduced on the market in July 1976 and came to be widely used also in general desktop computers using CP/M and other operating systems as well as in the home computers of the 1980s. It was also common in military applications, musical equipment, such as synthesizers, and in the computerized coin operated video games of the late 1970s and early 1980, the arcade machines or video game arcade cabinets.

The Z80 came about when physicist Federico Faggin left Intel at the end of 1974 to found Zilog with Ralph Ungermann. At Fairchild Semiconductor, and later at Intel, Faggin had been working on fundamental transistor and semiconductor manufacturing technology. He also developed the basic design methodology used for memories and microprocessors at Intel and led the work on the Intel 4004, the 8080 and several other ICs. Masatoshi Shima, the principal logic and transistor level-designer of the 4004 and the 8080 under Faggin's supervision, also joined the Zilog team.

By March 1976, Zilog had developed the Z80 as well as an accompanying assembler based development system for its customers, and by July 1976, this was formally launched onto the market. (Some of the Z80 support and peripheral ICs were under development at this point, and many of them were launched during the following year.)

Early Z80s were manufactured by Synertek and Mostek, before Zilog had its own manufacturing factory ready, in late 1976. These companies were chosen because they could do the ion implantation needed to create the depletion-mode MOSFETs that the Z80 design used as load transistors in order to cope with a single 5 Volt power supply. 

Faggin designed the instruction set to be binary compatible with the Intel 8080 so that most 8080 code, notably the CP/M operating system and Intel's PL/M compiler for 8080 (as well as its generated code), would run unmodified on the new Z80 CPU. Masatoshi Shima designed most of the microarchitecture as well as the gate and transistor levels of the Z80 CPU, assisted by a small number of engineers and layout people. 

In the early 1980s, the Z80 was the most commonly used CPU of all time, and, along with the MOS Technology 6502 family, dominated the home computer market from the late 1970s to the mid 1980s.

The Z80 offered many improvements over the 8080.

Electrical engineering[]


Zilog licensed the Z80 design to several second source manufacturers (and some East European and Russian manufacturers also made unlicensed copies). This enabled a small company's product to gain acceptance in the world market since far larger companies than Zilog, such as NEC, Hitachi, Toshiba and Sharp, started to manufacture the device. In recent decades Zilog has refocused on the ever-growing market for embedded systems (for which the original Z80 and the Z180 were designed) and the most recent Z80-compatible microcontroller family, the fully pipelined 24-bit eZ80 with a linear 16 MB address range, has been successfully introduced alongside the simpler Z180 and Z80 products.

Non-multiplexed buses (the 8080 had state-signals multiplexed onto the data bus). A special reset function which clears only the program counter so that a single Z80 CPU could be used in a development system such as an in-circuit emulator. The Z80 took over from the 8080 and its offspring, the 8085, in the processor market, and became one of the most popular 8-bit CPUs. Perhaps a key to the initial success of the Z80 was the built-in DRAM refresh, and other features which allowed systems to be built with fewer support chips (Z80 embedded systems typically use static RAM and hence do not need this refresh).

For the original NMOS design, the specified upper clock frequency limit increased successively from the introductory 2.5 MHz, via the well known 4 MHz (Z80A), up to 6 (Z80B) and 8 MHz (Z80H). CMOS versions were also developed with specified upper frequency limits ranging from 4 MHz up to 20 MHz for the version sold today. The CMOS versions also allowed low-power sleep with internal state retained, having no lower frequency limit. The fully compatible derivatives HD64180/Z180 and eZ80 are currently specified for up to 33 and 50 MHz respectively.

The Z80's electrical architecture[]

The Z80 electrical architecture.

The programming model and register set are conventional and similar to the related x86 family. The 8080 compatible registers AF, BC, DE, HL are duplicated as two separate banks in the Z80, where the processor can quickly switch from one bank to the other; a feature useful for speeding up responses to single-level, high-priority interrupts. This feature was present in the Datapoint 2200 but was not implemented by Intel in the 8008. The dual register-set makes sense as the Z80 (like most microprocessors at the time) was really intended for embedded use, not for personal computers, or the yet-to-be invented home computers. According to one of the designers, Masatoshi Shima, the market focus was on high performance printers, high-end cash registers, and intelligent terminals. The two register sets also turned out to be quite useful for heavily optimized manual assembly-language coding. Some software, especially games for the MSX, Sinclair ZX Spectrum and other Z80 based computers, took Z80 assembly optimization to rather extreme levels, employing the duplicated registers among other things to squeeze maximum performance out of the processor.


The then Western standard silicon\germanium etching process.

The Z80 CPU is an 8-bit based microprocessor. It was introduced by Zilog in 1976 as the startup company's first product. It was notably cheaper than it's peers. Along with the MOS Technology 6502 CPU it sparked a series of projects that resulted in the home computer revolution of the early 1980s.


Zilog Z80 CPU.
Category. Statistic.
Designed in. 1974.
Made in. 1976.
Transistors per chip. 8,500.
Power supply. Medium and low.
Still in use. A massively upgraded modern version is still used.
Nationality. America.


A 40 metal pin epoxy\plastic mini dual-in-line package (DIP-40) package.

Also see[]


  1. https://en.wikipedia.org/wiki/Zilog_Z80
  2. https://en.wikipedia.org/wiki/Transistor_count
  3. https://www.amazon.co.uk/s/?ie=UTF8&keywords=z80+processor&tag=mh0a9-21&index=computers&hvadid=3174905023&hvqmt=b&hvbmt=bb&hvdev=c&ref=pd_sl_6y1wbrvxbk_b
  4. http://www.z80.info/z80brief.htm
  5. http://z80.info/zip/z80cpu_um.pdf
  6. http://www.cpu-world.com/CPUs/Z80/