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
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.