Happy 40th ZX81

I was very honoured to be mentioned in ElReg today as they celebrated 40 years of the ZX81, my first computer. As a volunteer at The National Museum of Computing, I had a whale of a time a few years ago cataloguing their collection. Although space (and my cavalier attitude to deadlines) meant that not all of my thoughts could be published (also probably because they were not very good). I thought I’d post the full text here for prosperity.

My first encounter with a computer was my primary school’s Commodore PET, a beautiful tank of a machine on which I whiled away many a lunch break trying to create a Pac-man clone (I failed). Such luxuries were out of the question at home but then a small black square caught my eye while flicking through my teacher’s copy of Your Computer. Immediate pleadings and promises of many regular chores done without complaint led to a lump of polystyrene under the tree on Christmas Day. I still have no idea how my Dad sourced one, stories of delays were infamous. What Dad probably hadn’t counted on was my annexing of the family TV, his beloved Match Of The Day replaced by a white screen and a little black K, blocked from view by a 9-year old’s head. He eventually caved and bought a second-hand black and white portable TV for my room. That was it for my social life as I spent every evening in the familiar white glow of the screen, meticulously entering each example in the user guide and tentatively trying out my own ideas. I never did get a 16K Ram Pack, so never had the frustration of the famous ‘wobble’ resetting hours of work. My own pain came from the worn out power connector that had to be held down with sellotape or it would short-out without notice, wiping everything.

My wonderful ZX81 was replaced, of course, with the ZX Spectrum the following year. I reacquainted myself with my first real computer years later when I joined The National Museum of Computing as a volunteer and was tasked with cataloging the Sinclair connection. I learnt that a lot of schools bought ZX81s before the BBC Model B became the Government’s choice, eclipsing the ’81 like the starship in the opening sequence of A New Hope.

As a result of the many donations from schools, over the years TNMoC has amassed enough ZX81s to, as a fellow volunteer put it, ‘tile a small bathroom’. This had led to a few oddities turning up. Sir Clive famously claimed the ZX81 could power a nuclear power station (just make sure there’s some blu-tac on that RAM pack) and we did find comprehensive plans for a home heating system all run from a small black box. A complex system of relays brought mains electricity frighting close to the expansion port and I did wonder what became of this ambitious project and whether the fire brigade had any involvement.

Our favourite donation though, caused a minor sensation when it came to light. ZX81s were very hackable machines and the the most common modification was replacing that awful keyboard with a custom case. Some braver folk would then use the additional space for other bits and pieces. This one machine, who I nicknamed ‘Bluto’, was so crammed full of expansions we struggled to identify all the various cards connected up. This completely self-contained Frankenputer brought together the motherboard, PSU, RAM pack and a mysterious unmarked expansion card. These sat in case that housed a full-size mechanical keyboard and printer. There was even built-in cooling. Some detective work by curious fans discovered the mystery board was a ROM containing accounting software and some games. We would love to know who built this and what it was used for. If that person is out there, we’d like them to know that Bluto is still fully working and carefully stored at The National Museum of Computing.

Bluto, with the mysterious ROM next to the 16K RAM Pack
Still working after all these years…

P.S. I still have a few working ZX81s, one I built from an original kit (I know, heathen) and one modded for composite output. Might fire one up tonight.

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