z80

123 Articles

Multitasking On The Humble Z80 CPU

November 1, 2025 by 28 Comments

Multitasking is something we take for granted these days. Just about every computer we use, from our desktops to our phones, is capable of multitasking. It might sound silly to implement multitasking on lower-spec machines from many decades ago, given their limited resources, but it can be done, as [bchiha] demonstrates on a Z80-based machine.

[bchiha] has achieved pre-emptive multitasking on the TEC-1G Z80 computer, a modern reimagining of the classic Talking Electronics TEC-1 from the 1980s.  The proof of concept code allows running up to eight separate tasks at once. Task switching runs on interrupts, triggered at approximately 50 Hz. When an interrupt fires, the CPU registers are transferred onto that task’s stack, and the next task’s stack is swapped to the stack pointer to allow execution of the new task to proceed. There is an overhead, of course, with [bchiha] noting that the task swapping routine itself takes about 430 clock cycles to run in between tasks.

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Recreating A Homebrew Game System From 1987

October 29, 2025 by 10 Comments

We often take for granted how easy it is to get information in today’s modern, Internet-connected world. Especially around electronics projects, datasheets are generally a few clicks away, as are instructions for building almost anything. Not so in the late 80s where ordering physical catalogs of chips and their datasheets was generally required.

Mastering this landscape took a different skillset and far more determination than today, which is what makes the fact that a Japanese electronics hobbyist built a complete homebrew video game system from scratch in 1987 all the more impressive.[Alex] recently discovered this project and produced a replica of it with a few modern touches.

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Decorate Your Neck With The First Z80 Badge

September 28, 2025 by 4 Comments

Over the years, we’ve brought you many stories of the creative artwork behind electronic event badges, but today we may have a first for you. [Spencer] thinks nobody before him has made a badge powered by a Z80, and we believe he may be right. He’s the originator of the RC2014 Z80-based retrocomputer, and the badge in question comes from the recent RC2014 Assembly.

Fulfilling the function of something you can write your name on is a PCB shaped like an RC2014 module, with LEDs on all the signal lines. It could almost function as a crude logic analyser for the system, were the clock speed not far too high to see anything. To fix this, [Spencer]’s badge packs a single-board RC2014 Micro with a specially slow clock, and Z80 code to step through all memory addresses, resulting in a fine set of blinkenlights.

Thus was created the first Z80-based event badge, and we’re wondering whether or not it will be the last. If you’re curious what this RC2014 thing is about, we reviewed the RC2014 Micro when it came out.

a Coleco Adams console on a desk

Coleco Adam: A Commodore 64 Competitor, Almost

July 21, 2025 by 65 Comments

For a brief, buzzing moment in 1983, the Coleco Adam looked like it might out-64 the Commodore 64. Announced with lots of ambition, this 8-bit marvel promised a complete computing package: a keyboard, digital storage, printer, and all for under $600. An important fact was that it could morph your ColecoVision into a full-fledged CP/M-compatible computer. So far this sounds like a hacker’s dream: modular, upgradeable, and… misunderstood.

The reality was glorious chaos. The Adam used a daisy-wheel printer as a power supply (yes, really), cassettes that demagnetized themselves, and a launch delayed into oblivion. Yet beneath the comedy of errors lurked something quite tempting: a Z80-based system with MSX-like architecture and just enough off-the-shelf parts to make clone fantasies plausible. Developers could have ported MSX software in weeks. Had Coleco shipped stable units on time, the Adam might well have eaten the C64’s lunch – while inspiring a new class of hybrid machines.

Instead, it became a collector’s oddball. But for the rest of us, it is a retro relic that invites us to ponder – or even start building: what if modular computing had gone mainstream in 1983?

SymbOS Is A Funhouse Mirror Look At A Future That Never Was

July 19, 2025 by 66 Comments

The Z80 might be decades obsolete and a few years out of production, but it’s absolutely a case of “gone but not forgotten” in the hacker world. Case in point is SymbOS, a multitasking OS for Z80 machines by Amstrad, Sinclair, and the MSX2 family of computers that updated to version 4.0 earlier this year.

The best way to describe SymbOS is like looking at an alternate reality where Microsoft created Windows 95 ten years early to put on the MSX instead of the BASIC they were paid to provide. SymbOS 4.0 comes even further into alignment with that design language, with a new file explorer that looks a lot like Windows Explorer replacing (or supplementing) the earlier Midnight Commander style utility in version 3.

Thanks to the preemptive multitasking, you can listen to tracker music while organizing files and writing documents, and even play a port of DOOM. Chat with your friends on IRC while watching (low res) videos on SymboVid. If you’re looking for productivity, all the old business software written for CP/M can run in a virtual machine. There’s even an IDE if you can stand the compile times on what is, we have to remember, an 8-bit, 1980s machine. It’s hard to remember that while watching the demo video embedded below.

The operating system supports up to 1024 KB of RAM (in 64 KB chunks, of course) and file systems up to 2 TB, which is an absolutely bonkers amount of space for this era’s machines.  One enterprising dev has even got his CPC talking to ChatGPT, if that’s your jam. You can try SymbOS for free online on an MSX emulator, or toss it onto a spare Raspberry Pi.  If you’re feeling adventurous, there’s a port in the works for the Isetta TLL retrocomputer.

This isn’t the first modern OS we’ve featured for the Z80, the processor which will live forever in our hearts and tapeouts.

Thanks to [Manuel] for the tip.

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RADUGA: The Retro Computer From Behind The Curtain

May 14, 2025 by 7 Comments

When [Kasyan] was six years old, he saw a RADUGA computer, a Russian unit from the 1990s, and it sparked his imagination. He has one now that is a little beat up, but we feel like he sees it through his six-year-old eyes as a shiny new computer. The computer, which you can see in the video below, was a clone of the Spectrum 48K.

The box is somewhat klunky-looking, and inside is also a bit strange. The power supply is a — for the time — state-of-the-art switching power supply. Since it wasn’t in good shape, he decided to replace it with a more modern supply.

The main board was also not in good shape. A Zilog CPU is on a large PCB with suspicious-looking capacitors. The mechanical keyboard is nothing more than a array of buttons, and wouldn’t excite today’s mechanical key enthusiast.

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What’s An LCR Databridge?

May 13, 2025 by 6 Comments

[Thomas Scherrer] has an odd piece of vintage test equipment in his most recent video. An AIM LCR Databridge 401. What’s a databridge? We assume it was a play on words of an LCR bridge with a digital output. Maybe. You can see a teardown in the video below.

Inside the box is a vintage 1983 Z80 CPU with all the extra pieces. The device autoranges, at least it seems as much. However, the unit locks up when you use the Bias button, but it isn’t clear if that’s a fault or if it is just waiting for something to happen.

The teardown starts at about six minutes in. Inside is a very large PCB. The board is soldermasked and looks good, but the traces are clearly set by a not-so-steady hand. In addition to AIM, Racal Dana sold this device as a model 9341. The service manual for that unit is floating around, although we weren’t able to download it due to a server issue. A search could probably turn up copies.

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