Happy 30th Birthday, ZX81

The Sinclair ZX81 home computer is 30 today. It and its variants such as the Timex-Sinclair 1000 sold over one and a half million units – which combined would have the processing power of around 38 Intel Core i7 Extreme Edition 990x chips, albeit sharing a positively meagre 1.5GB of RAM.

It plugged into a television, loaded programs at 30 characters a second from a cassette tape, had no lower case, sound, colour or graphics, sported a dead-flat keyboard with the usability of a slab of granite, and could manage maybe fifty lines of BASIC before filling up.

It was entirely, unashamedly wonderful.

Coming just 30 years after the world's first business computer, it's hard to realise today just how wonderful it was.

I built mine in an evening from a kit — which cost £50, the most money I'd ever spent on anything. It had taken two months to arrive, due to that characteristic 'allow 28 days for delivery' time dilation effect for which Sinclair Research was famous. Although I'd ordered it before my (far richer) best friend had decided he wanted one too, WH Smith started to stock the finished product in the intervening period. He just waltzed in and bought one while I was still staring at the letterbox.

Forgive and forget? Hardly. Nick Clarke, your card is marked. Forever.

It only took an evening to build because it was extraordinarily simple: five chips, a handful of resistors, diodes and capacitors, and maybe eight screws. Three of the chips were memory, one was the awesome Z80A microprocessor, and one was a Ferranti Uncommitted Logic Array (ULA), the precursor to the ASIC technology that continues to fuel so much advanced electronics. That was the first use of such a chip in a consumer product: by replacing some 40 logic chips from the previous ZX80 design, it made the whole thing possible at a price that the penniless could afford.

That was a lesson in technology that I have never forgotten: it doesn't matter how magical something is, if you can't afford it it's useless to you. And if enough people can afford something, it can change the world. Who has time for technology that can't change the world?

The ZX81 was a genuine world-changer. Its lack of features and cost-pared simplicity meant that every last detail was accessible to the inquisitive. And each discovery had immediate benefits. No sound? Well, if you made the bit of the circuitry that recorded programs to the cassette tape waggle up and down fast enough, you could create tones and play them through an amplifier.

To make that happen, you needed to learn a smidgeon of machine code; the manual had a full list of the codes in the back, and just enough information to bootstrap the reader into a world of experimentation. If you put in the work, you could teach yourself everything about what I later discovered was the Von Neumann architecture underpinning all of computing. But it wasn't work: it was intensely engaging, captivating and rewarding fun.

Splat some data into the right bit of memory, and it appeared on screen. Copy it around a bit, and the screen animated. Capture some data from the keyboard, and the animation became interactive. In perhaps two or three evenings, you had the beginnings of a game, or a doodle maker, or a graphic formula explorer. And if you tweaked it a bit, you could play the data as music — so a sequencer, a morse code sounder or a sound effect generator could fall out of the same code.

Quite a lot of the kids who found that secret garden went on to make it their life's work, the first digital generation — and look how far that's come in thirty years. Once you get the taste for teaching yourself, it never goes away; just as well, as I may not have been the only person whose schoolwork took a back seat to bedroom autodidacticism.

The ZX81's simplicity also spawned an extensive industry in add-ons. Keyboards, memory extensions, sound cards, colour graphics – you could build up a ridiculously complex system from the adverts in the back of the magazines. Or you could build such things yourself: each month brought more circuits and how-tos in the specialist literature which foreshadowed the online open hardware movement by decades.

My first ZX81 ended up unrecognisably mutated, sitting in an aluminium box festooned with knobs and symbiotically interwoven with a hacked-about CB radio — I'd built, it turned out, a frequency-hopping system curiously similar in concept to one I encountered a couple of years later sitting in an electronic warfare pod in the labs of a large defence contractor. That cost a bit more than £50, mind, and could wipe out TV reception over rather more than the half-mile radius mine unfortunately proved to reach.

Sinclair Research itself didn't quite get the hang of learning from the ZX81. Although the ZX Spectrum was even more popular, it had enough problems in production to wipe out any profits it made, and Clive Sinclair's disdain for giving people what they wanted led in too many fruitless directions for survival.

But by then, the magic had happened. We'd tasted the ability of computing to take our thoughts and give them an independent existence as live, active chains of effect, and we'd begun to see where this could lead. Thirty years later, we're still at it – and the world is changing faster with every breath.

I haven't spent a better fifty quid in my life.