T his post is an upvote for Tynemouth Software's ZX81 reversible Internal 16K RAM upgrade . Their instructions are easy enough for even me to follow and don't involve cutting tracks. This is the ZX81 I've had out on display and used whenever I wanted to. It's an issue 1 and was probably a kit judging by some very untidy assembly. It has a ZX8-CCB composite video mod and an external keyboard fitted. On board it has two 1k x 4-bit chips. The ZX81 originally came with 1k on board. Thanks to a trick with compressing the display in ram, that was enough to type and run a small program but you soon felt the limitations. Back in the early 80s, the solution was a 16k ram pack which plugged into the back[1] and this is the way I've been using this particular machine. These ram packs are notorious for 'ram pack wobble'. Even if fastened into place, you can still randomly find your work disappearing. This is a very reliable solution using a more modern 32k chip (half
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