Retro Computers - Sinclair ZX81 - Retro Computer

Sinclair ZX81ZX 81
Peolpe really warm up to Uncle Clive.

The Sinclair ZX81 was the follow up to the ZX80 and was released by Sinclair Research Ltd in 1981. Once again, the machine was named after it's year of release. Like it's predecessor, it became a popular machine in homes the length and breadth of the UK.

As with the ZX80 the processor was a NEC Zilog Z80-compatible, running at a clock rate of 3.25 MHz. The system ROM had grown to 8192 bytes in size and the built in BASIC now supported floating point arithmetic. It was an adaptation of the ZX80 ROM by Steve Vickers, who was one of the authors of Sinclair BASIC. The new ROM also worked in the ZX80 and Sinclair offered it as an upgrade for the older ZX80 for a time.

Like the ZX80, the ZX81 was quite a basic piece of kit. The base system had only 1KB of RAM on board. This RAM was used to hold the computer's system variables, the screen image, and any programs and data. The screen was text only, 32 characters wide by 24 high. Blocky graphics with a resolution of 64 by 48 pixels were possible (created in BASIC using the PLOT command), which made a selection among a set of 16 graphics characters.

The ZX81 used a resizable screen buffer meaning that it could be expanded or shrunk (depending on the amount of installed memory and the amount of free space at any given time). No colours were available and the machine once again had no sound generator. The 'keyboard' as such was not a proper keyboard, with Sinclair once again going with the membrane pad similar to the ZX80.

Once again, sticking to a tried and tested formula, the ZX81 was originally sold via mail order in kit form which requiried soldering (priced at an incredibly cheap £49.95) or assembled (a still more than reasonable £69.95). The USA was treated to the same deal, with a ready made ZX81 costing roughly $100.

A deal struck with high street retailer W.H.Smith saw the ZX81 and all accessories being sold on the high street. The ZX81 retailled at £69.99, ZX 16K RAM pack went for £49.99 and the ZX Printer was available for £49.99.

Apart from having more BASIC commands than it's predecessor, it also had two modes of operation. Fast mode (the same as a ZX80) and slooooow mode. Slow mode made it like all other computers as in it refreshed the display all of the time. No Boney M home discos here.

The ZX81 was a simple affair and contained only four main chips. The ROM, Z80A CPU, 1KB RAM and the Ferranti custom-made chip. The ready made machines were assembled by Timex Corporation.

A vast range of peripherals were developed for the machine such as: 3.5" floppy disk units proper keyboards high resolution graphic cards RS232 or Centronics interfacesRAM expansions, etc...

In fact, it was possible to make a pretty powerful computer by upgrading the ZX81

The range of expansion options was really quite marvellous! For instance, a company called Memotech created a whole range of modules which would 'chain link' together one after another. The hardware pieces used velcro pads to secure to each other as there were no mechanical locking on the edge connectors.

So, all in all you could have additional memory (up to 128KB!), high resolution graphics, disc controllers, joystick controllers, serial ports etc etc. Holy smoke, with all of this kit you'd be the talk of the town. If you lived in GeekTown anyway.

A Popular add-on naturally was a replacement keyboard. Proper mechanical keys could be stuck over the membrane keyboard. Others involved re-housing the ZX81 inside a new, larger case with a 'proper' keyboard on it.

The options were almost endless. Sadly the power supply wasn't particularly stable making glitches commonplace which could result in system resets, usually just as you were entering the last line of a 2000 line program which would make you shout out 'Oh Shoot!'. Why did you never bother saving to tape until the whole thing had been completed?

'Ram Pack Wobble' was another expansion 'feature'. If you were lucky enough to have the 16KB RAM pack attached, sometimes moving the machine would cause the RAM pack to wobble in it's edge connector and cause the ZX81 to re-set. Again, this could break your day. A bit of blu-tac to secure the pack and you'd be back in proper business though. Those were the days of user tinkering.

The ZX81 was sold in the USA by Sinclair Research (from its facility in Nashua, New Hampshire). Timex Sinclair (a joint venture with Timex - as if you couldn't guess), also produced an enhanced ZX81 for the US market as the Timex Sinclair 1000 (or TS1000). This shipped with twice as much RAM (2kB) and featured mimetic-polly-alloy. It also had detailled files. A further enhanced model (the TS1500) expanded the RAM to 16KB.

Like the ZX80, the ZX81 was also cloned around the world. Microdigital produced two ZX81 clones (the TK 82C and the TK 83), and a TS1500 clone (the TK 85). Prológica produced the NEZ-8000 and the enhanced CP-200 and CP-200S models. Other clone models cropped up in various countries around the globe.

Looks wise, the ZX81 was a sleek and stylish machine. Far cooler looking than it's predecessor, the black case and Sinclair logo coupled with the almost 'silvery' membrane keyboard was ahead of it's time.

The ZX81 built up a reasonable software library. Quite a few computer games were available to play, most of them featuring very basic monochrome graphics. There was even a version of chess squeezed into 1K! Even basic 3D games were released, such as 3D Monster Maze. Someone even ported Manic Miner to it! Developers managed to get alot out of one of these machines.

More games sells more machines, and the ZX81 went on to sell roughly 1.5 million units. Not bad eh?

Turn around, look over your shoulder and give the machine more than a passing glance. A fine retro computer.

We recommend trying to pick up one of these machines.
Look at computers for sale online or even locally.

If you don't want to get hold of the real hardware then try and download an emulator and
download those classic games. Alternatively you could try and play them online.

MACHINE TYPE: Home Computer
RELEASE YEAR: March of 1981
BUILT IN LANGUAGE(S): Sinclair Basic
KEYBOARD: Touch-sensitive keyboard, 40 keys
CPU: Zilog Z80A
SPEED: 3.5 MHz
RAM: 1KB (901 bytes available, up to 128KB with expansion)
TEXT MODES: 32 x 24 (2 lines are reserved for system messages and commands)
COLORS: Black and white only
SIZE / WEIGHT: 167 x 175 x 40 mm / 350
I/O PORTS: Z80 Bus, tape, video
PRICE: Kit £50 (UK June 1981). Ready made £70 (UK June 1981)

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