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Sinclair ZX81

Posted by Big Boo on November 13th, 2008

Sir Clive Sinclair has had his share of successes (the ZX Spectrum) and failures (the C5) but the ZX81 (known in the US as the Timex Sinclair 1000), despite being laughable as a computer these days, was at the time one of his success stories.

Unsurprisingly released in 1981, it was the follow up to the lesser known ZX80 which was similar in specification and looks, albeit the ZX80 being white with blue keys.  The machine had a Z80 processor, a cheap and reliable CPU that was used in many 8-bit computers, and a measly 1K of RAM, although the pictured additional RAM pack could boost it to a whopping 16K!

Graphically it could only display black or white pixels on a 256×192 sized screen, and additionally it was not possible to affect pixels individually.  Instead the user had a 32×24 array of characters that could be displayed on screen.  While most of these were letters or punctuation, some of the characters contained little blocks of 4×4 pixels, so a very low resolution image of 64×48 could be produced with care!  Later in its lifespan some clever coders found a way of affecting pixels individually, but by this time most ZX81’s had been retired in favour of something newer and more powerful.

The ZX81 was also completely mute, and had no way of producing any kind of sound.

Programs were stored on audio cassette tape and loaded using a standard tape recorder, although this could prove to be a tricky prospect to get the volume levels just right.  Many people would deliberately cover their volume control with blue tac or sticky tape once the right level was found to save them tearing their hair out later!

Another bizarre feature of the ZX81 was that it had fast and slow modes.  In fast mode the computer was completely unable to display an image, as the CPU was required to make the screen display appear, so many programs would warn the user that some lengthy processing was about to occur before blanking the screen.

Most of the games to appear on the ZX81 were arcade style conversions of games like Space Invaders or Pacman, but the stand out game that just about every ZX81 owner must have owned was the brilliant 3D Monster Maze.  Basically just a simple maze game it was pretty astounding at the time for the suspense generated by not being able to see where in the maze the Tyrannosaurus Rex who was chasing you was located.  When you did catch sight of T-Rex panic would set in as you tried to get away from it, normally ending in death as the dinosaur gradually became larger and more detailed on the screen before finally ending with a display of its massive sharp teeth filling the entire screen.