Sinclair ZX81

In these days of fast Pentium PC's and Gigabyte hard drives, it is easily forgotten that the early days of the home computer produced machines considerably more humble and yet they sparked a technological revolution the reverberations of which are still all around us today. And at the root of this tide of new technology was the Sinclair ZX81, at least in the UK. There were other computers around at the time but they were hideously expensive and manufactured in the states. If computers were to be become truly successful then they had to be made available to the masses at an affordable price and not require an encyclopaedic knowledge of their inner workings in order to be able to use them. And it is here that the ZX81 was a triumph. So what is a ZX81 and why was it such a hit? I'll try to answer that in the coming pages.

The first computer out of the Sinclair stable was not the ZX81 but the ZX80 launched in 1980 and sold principally as a kit by mail order for around 79 pounds for assembly by enthusiasts. It was a curious looking white thing, not at all like the black computer we now associate with Sinclair kit. It was very underpowered without floating point decimal maths and only 1k of memory with the familiar metal membrane keyboard and a 4k BASIC held in ROM. It did have a Z80 processor running at 3.5 Mhz (the original PC only ran at 4.77 Mhz) and a slot where extra hardware could be plugged in. The whole thing was A5 size and about an inch deep and was incredibly light.

A key problem at the time was one of display and storage which was keeping costs of computers high. The ZX80 solved the problems by employing both a common or garden black and white Television set for display and a domestic tape deck for storage. The people buying the machines at that time were enthusiasts wanting to get close to computers that were in the main still large, complicated to operate and expensive to buy. That is the legacy that Sir Clive Sinclair has left and it has largely been forgotten.

1981 saw the launch of the upgrade of the ZX80 called (unsurprisingly) the ZX81. It was cheaper too at around fifty pounds for the kit or around seventy pounds for a fully assembled and functional unit. ZX80 owners were offered the larger 8k ROM as an upgrade which enabled the use of the new thermal printer. The chip count was reduced (only four in all) using a Ferranti custom chip and the 1k internal memory could be boosted to a cool 16k using an add on RAM pack which was the capacity of most desktop machines built only several years before (in fact CP/M 1.4 was designed for machines with just that amount of memory).

Of course it was not without it's problems. The 16k Ram Pack arrived late and tended to wobble causing crashes. The keyboard though useable was not good enough for fast touch typing. Software was slow to load from tape as it ran at a rather sedate 300 baud. The screen was limited to upper case characters and a few graphics blocks in black and white only. There was no sound. The display was updated by the processor which tended to slow it down so a new BASIC keyword was provided called 'FAST' that would switch the display off allowing calculations to be made at full speed. The display could then be reinstated using 'SLOW'. There was no software supplied with the machine when new, not even a demo tape. There were no joystick ports or printer interface.

Doesn't seem to have much going for it does it? WRONG! Most of the problems were solved by third party suppliers providing programs and add-ons independently of SRL (Sinclair Research Limited). Better Ram Packs became available in some cases adding 63k of memory. High Resolution graphics and sound modules also became available. Slow load times were enhanced by clever programming making a 16k program load in under a minute. Keyboards could also be added ranging from a stick-on one to a full size typewriter style keyboard. BASIC programmers also discovered that the ZX81 could be persuaded to produce noises through the TV speaker.

Add to this an extensive range of software available from SRL and a host of other companies. There was even a Flight Simulator and Word Processor written for it. Machine Code Assemblers and a host of other tools also added to the possibilities. But most importantly, high street vendors such as WH Smiths and Boots stocked the machines so anyone could walk in and buy one.

These were heady days with magazines like Popular Computing Weekly (now no more - sniff) publishing listings in both machine code and BASIC for both 1k and 16k machines. 1k doesn't sound like much but it is enough to learn BASIC and some machine code. The computer could be used by just about anyone and the manual supplied with it was excellent. It is difficult now to visualise the kind of excitement the ZX81 generated particularly as it was so humble. But it showed that computing could be both cheap and useable. The computer boom was well and truly on it's way. It wasn't so very long ago that the ZX Spectrum was the biggest selling UK Home Computer and Games Console though sadly that is not now the case as Amstrad have discontinued production. Nevertheless, for a machine well over ten years old (about the same age as the IBM PC) it sold remarkably well despite a change of ownership and design, a tribute to it's designer Sir Clive Sinclair and others at Sinclair Research Ltd. (SRL). The Spectrum presents an excellent field for the ardent collector of defunct equipment with most later Plus 2's down to as low as ten pounds on the second hand market. But it's chequered history can lead to confusion as to what machines will run what software and which peripherals will work and those that won't. I hope to shed a little light on the subject in this and succeeding articles.

For the moment however, I would like to ponder the role that both the ZX81 and Spectrum were to fulfil. Both machines were seen by their creator (Sir Clive Sinclair) to be educational and were designed with that in mind. But people used them for games and the machines were never designed for such a purpose. The Spectrum in particular uses colour in a fairly low resolution and the way memory is arranged and the lack of any form of sprite handling makes programming games on it very difficult. There are no custom chips to handle the display so the CPU has to do all the work. It is phenomenal just what was achieved by programmers but in the end it could not compete with the consoles and for that reason the Spectrum died.

And yet the Spectrum has much to offer the current generation of potential users. No more can we go into a shop and buy a computer for less than 100 pounds. You can buy a console (at the time of writing) but it is certainly NOT a computer and will teach a child (or an adult) very little about the computer and how it works. It is just as important today (perhaps more so) to know at least something about computers as the world in which we live becomes a technological jungle.

True there are computers in high street shops available but despite the hype they are not an ideal starting point for a novice user to be begin and it is certainly not a cheap hobby to be indulging in for a bit of fun. And yet people just would not buy a sub 100 pound computer because it won't run any of the software that they perceive they need because of pressure from the media and friends.

I am convinced that there is a market for a cheap computer that could be plugged into a TV although a faster way of loading and saving software will need to be devised. Software could be sold in the high street composing of games but also a range of good quality educational software. If the machine was compatible with an older computer (like the Spectrum) then software houses could release their back catalogue that would involve minimal coding and provide money for new projects. If it should fail to happen then at least they will have lost very little. The boom in small computers could make a come back even now. Or am I just dreaming? There were rumours that Amiga Technologies were ready to release a new version of the C64 but it never happened...but you never know...