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ZX 81

Cliff Peterson's experience: The ZX-81 that I bought was a kit.  Shortly thereafter, I noticed that the Timex Sinclair 1000 was released. The main difference was the RAM - the TS1000 had 4k, the ZX81 had 1k. As I looked at the ZX81's motherboard, I noticed that the printing alluded to 4k.  There was an electronics store near my house, and I was able to locate a 4k memory chip.  After replacing the original chip, I had 4k!  Since nearly 700 bytes of the RAM was consumed by the system, that meant I had gone from 300 bytes to 4000, so I really had a hot machine! Many games were available for the ZX81, mostly dots and stuff moving up the screen.  The most common was a version of asteroids.  In order to play this game, I installed a DB9 connector in the side of the case, wiring the left,right,up,down and fire buttons to key contacts inside.  Thus, where asteroids used A and Z as left and right, an atari joystick worked great! Popular hardware modification, by Mark Slabbert: Popular hardware modification was to install a simple video inverter circuit with an external switch to display white characters on a black background. This made the display easier on the eye.