There are few companies still selling 1K ZX81 games and Selec Software is one of them.

The programs may not be anything special but the way in which they are fitted into the 1K memory space must be praised.

Two of the best cassettes in the range include 1K The Invaders and 1K ZX Panic/ZX Squash. All the games on both cassettes are in machine code and their speed is the main attraction.

The Invaders is a typical game of Space Invaders. You have to hide beneath your three laser bases and, when you can, get as many laser shots as possible at the enemy invaders.

The control keys are a little awkward to handle but once you are used to them there should be no difficulty about enjoying the game to the full.

Panic is a target-shoot game in which you have, yet again, to bag as many aliens as you can. The game can become a little tedious after about half an hour of continuous play, but if you want to play something else you can change to side two of the cassette and play ZX Squash.

That involves two players who must take turns to hit a ball against a wall.

If you do not like the idea you could always imagine that it is a two-player version of Breakout.

Both tapes can be obtained, for £3.50 each, from Selec Software, 37 Councillor Lane, Cheadle, Cheshire.