Zilog Z80

» see zilog.com as it lived, on the wayback machine

~ the obituary ~

Federico Faggin had already done the physical design of the Intel 4004 and led the 8080 when he left Intel at the end of 1974. Masatoshi Shima, who had worked on both with him, followed in February 1975. Exxon put up half a million dollars that June, and the company they named Zilog spent a year building a processor whose entire commercial argument was that it ran everything the 8080 ran, only better.

It shipped in July 1976. Being binary compatible with the 8080 meant existing software ran on it from day one, and the design fixed the parts of the 8080 that were awkward to build around: one supply voltage instead of three, and dynamic memory refresh handled by the processor itself, which took a chunk of support circuitry off every board. It also carried a second full set of registers you could swap to in a single instruction, which is why interrupt handling on Z80 machines is fast and slightly strange.

Those are engineering details and they decided the eighties. Fewer parts on a cheaper board, with the software already written: the Z80 became the default answer for anyone building a computer that had to hit a consumer price. CP/M ran on it, which made it the business standard before MS-DOS existed, and then the home machines arrived and it was in nearly all of them.

~ the case file ~

~ what it was inside ~

The TRS-80 and the Osborne 1 and the Kaypro luggables ran on it. So did the ZX80, the ZX81, the ZX Spectrum, the Amstrad CPC and every machine built to the MSX standard. Sega used it as the main processor in the Master System and the Game Gear, then kept it in the Mega Drive as a sound co-processor and a compatibility layer. The original Pac-Man board is a Z80. Texas Instruments put it in graphing calculators that were still on school supply lists in the 2020s.

Turkey met it through Sega, mostly. The Master System and its clones were the console that actually reached Turkish shops in the early nineties, and there is a Z80 in there doing the work, which means a great many people spent their childhood on this processor without ever hearing its name. By the time I was studying computer engineering the chip had turned into a teaching object, an architecture simple enough to hold in your head while somebody explains what a register file is. It was already twenty five years old and still the clearest thing to learn on.

~ the notice ~

On 15 April 2024 Zilog, by then a subsidiary of Littelfuse, published a product change notification covering thirteen parts in the Z84C00 family, which is to say the standalone Z80 CPU in every package it still came in. The stated reason was that the wafer foundry would be discontinuing support for the product. Last time buy was set for 14 June 2024.

That is the actual death certificate: not a decision that the chip was obsolete, but a fab deciding it no longer wanted to run a process from another era. Distributors sold out of the remaining stock within days, mostly to people building new computers around a part that had just been declared finished.

~ what still runs on it ~

The eZ80 line was left out of the notice and is still sold, so the instruction set has not stopped shipping even though the original chip has. Open source implementations of the Z80 exist in Verilog and run on FPGAs, and at least one project is putting a compatible core into a drop-in DIP40 package for people replacing dead silicon in forty year old machines.

Zilog ran the Z80 for 48 years, which is longer than most companies last and considerably longer than any product line has a right to expect. Faggin was 34 when it shipped and 82 when the last orders closed.

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