ZX81

Close up of Sinclair ZX81
Photo by Barney Livingston / CC BY SA

With the 30th anniversary of the Mac just gone by I thought it would be nice (and a little self indulgant!) to write about some of the computers I’ve owned in the past. I use Mac’s almost exclusively now but it wasn’t always the case.

About the same time as Steve Jobs was wowing the crowds with the launch of the first Mac I had one of these bad boys. The Sinclair ZX81 was the successor to the ZX80 and was designed first and foremost to be low cost (costing £69.95 fully assembled or £49.95 in kit form). It had just 1Kb of RAM, no sound capabilities and low resolution monochrome graphics. The machine could not run at full speed and also maintain the display so it would flicker every time you pressed a key or the machine did a calculation. You could switch it to ‘SLOW’ mode which would make the computer concentrate on maintaining the display at the expense of slowing the running program down. Despite all these limitations the ZX81 was very successful and sold over 1.5 million units.

It was possible to plug in a RAM pack and expand the memory vastly to 16Kb. The RAM pack plugged into the back of the machine and was a frequent cause of crashes when it wobbled. Users would commonly stick the pack in place with Blu-Tack to try and prevent this.

Typical ZX81 setup
Photo by Mike Cattell / CC BY

The 1Kb of memory certainly made it challenging to write programs for, although some clever programmers were able to do some amazing things with it. One of the best examples of this is 1K ZX Chess, which fits a fairly complete chess engine into 672 bytes!

By far the most memorable thing about the ZX81 was the keyboard. To keep the cost down it was fitted with a simple membrane keyboard. The keyboard was pretty terrible to use and spawned a number of addons to try and improve it. Some even involved putting the ZX81 into a whole new case!

Despite all of its shortcomings, the ZX81 was an enjoyable computer to tinker with, and it started a life long love of computing for me.

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