Saturday, 25 October 2014

A bit of geek nostalgia

 Anyone remember this? The Sinclair Z80, one of the first reasonably priced, ready built home computers to be found in the UK. You could either buy one ready built for £99.95, or save a few pounds by buying it as a kit and put it together yourself for just under £80. You needed to be fairly handy with a soldering iron, but that was no problem to me since soldering was part and parcel of my regular job. Of course once I knew it existed, I had to buy one as soon as I could and I was able to afford it because I had been saving up.
Not your usual kind of saving, but a long time back, just before decimalisation of the British currency, I had been keeping all the silver content coins in my change. Before decimalisation, coins had retained the same denominations for well over one hundred years and so there could be coins with all the different heads of past monarchs on them, including the odd Victorian coin. All silver coins were at one time pure silver and right up until 1946, there was some silver content in these coins and all this silver bullion was still circulating as loose change. So like a number of others around that time, I had collected a large set of pre-decimal coins, putting them into year sets and many of these were silver. Ten pounds value of the silver coins I had collected, I had worked out at current silver prices would earn me enough to buy a Z80 kit and have some money left over. I took the coins to a small dealer in London, I had seen advertise, who was offering a good rate of exchange.

 The place I went to turned out to be a really seedy looking shop in the Holloway Road. It was gloomy and unwashed looking inside and I was beginning to have some doubts that I was doing the right thing. The guy behind the counter was not very reassuring either, being just as scruffy as his dingy shop and as I approached the counter a large German shepherd lifted its head and growled menacingly. The guy never said a word the whole time and I offered him the packet of coins, thinking ‘I am going to be seriously ripped off here,’ whilst not quite having the nerve to turn around and walk straight out again. He counted the coins, weighed them and calmly peeled off one hundred pounds from a big roll of notes. I was astounded and very pleased because, despite my qualms, the guy had come across with a good deal and I had what I needed to buy my home computer and even some left over. 
The dog behind the counter in that shop looked a good deal less friendly than this one
The Z80 was not my first computer, a year or so before I had built a PipBug kit computer that I bought second hand from someone who had bought it and then decided they were not really up to the project.

The PipBug computer was about as minimal as you can get. It consisted of just a bare board, no keyboard, no power supply and no usable video output for a monitor. It had a whole 256 bytes of RAM. No that is not a misprint, not Gigabytes, Megabytes, or even kilobytes, there were just 256 memory cells and no means of storing programs you have written when you switched it off. To see what you were doing, it needed a terminal, something used with mainframe and expensive business computers at the time and one of those was way beyond my budget, so I built an Elector terminal kit, which provided all the electronics for a terminal without the screen or keyboard. You connected it to your TV for a display. I also had to build a keypad and a power supply.

It used machine code, so the keypad only needed sixteen keys or so plus a space and an enter key. This was easy to build and I was soon up and running, typing in a whole string of numbers in exactly the right sequence to get the device to display the word ‘HELLO’ on the screen. This after about twenty minutes of solid typing. My family were not impressed, but I was delighted and was jumping for joy. I was ecstatic, I had written my first machine code program and it worked. My enthusiasm did not last for more than a few weeks, because with no tape or disk storage, you always had to spend around twenty minutes or often much longer just to make something happen and what you got was not very spectacular or useful.

 When the Z80 came on the market, I was determined to upgrade. With the Z80, all the keys and display electronics were built in and all I had to do was connect it to a TV to get a display once I had put it together. The Z80 used BASIC and so now I had to learn that computer language. I had made a start at that too, because one of the things I had bought whilst still working in London was a Casio PB-100.

This was a programmable calculator which also ran on BASIC and I had used that to write short programs and so already had some knowledge of how to go about it, but it was still a steep learning curve.

To store programs and load programs on the ZX80, you had to use a cassette recorder, but since most households had one at that time, this was no real issue. A major problem of using a casette to store programs was the time it took to load a program. The accuracy of the reproduction of the cassette player was important. Any wear or dirt on the playback head would prevent a program loading and you would only know it had not loaded after you had waited for the tape to get to the end of the section containing the program you wanted. You could have more than one program on a tape, but had no way of indexing them unless you manually noted down the tape counter, assuming your cassette recorder had one and very few did, so even finding a program was problematical.
Pretty soon a generation of computer users had learned a new word, ’azimuth’. This related to the tape head adjustment, which had to be absolutely vertical or the higher frequencies of the recording were lost. On audio playback this merely muffled the sound a bit, but on a program recording the program would become unreadable. Since cheap cassette recorders were often not too well aligned, some would be a little off vertical. Borrowing a tape from someone else often resulted in failure. Adjusting the head to match the borrowed tape worked but then your old ones would not work, likewise if you had to buy a new cassette recorder your old tapes would not load until you readjusted the azimuth. So computer buffs became very good at adjusting and re-adjusting the playback head of cassette recorders.

The Z80 had some major idiosyncrasies besides this. It only had 1kb of memory, which was a bit limiting, even though it was four times my old PipBug. It could only output the display when the processor was not working on a program. This meant that the results of your program were only displayed at intervals and no animation was possible. The display was black and white and mostly characters with a few crude blocks for simple graphics.

 The following year Sinclair released a much improved computer known as the ZX81. This allowed proper displays that could be animated, but still only in black and white. Both the ZX80 and the ZX81 could be expanded to 16kB of memory if you bought the expansion pack. I eventually bought a ZX81 and an expansion pack and I started to write simple games programs. You could by now buy a lot of software for the ZX81, including a word processor and it is rumoured that Terry Pratchett wrote his first Diskworld novel, The Colour of Magic, on a ZX81.

The year after that, building on the success of the ZX80 and even greater success of the ZX81, Sinclair released the Spectrum. A colour computer that had 16kB of memory built in. This proved to be a real winner for Sinclair and sold millions. Long after its release in 1982, I upgraded from my ZX81 to a spectrum.

Now the boys were old enough to become interested in them and soon I was sitting watching them use my computer, unable to get near until after they had gone to bed.

The Spectrum was much more like a home computer should be. It was able to produce colour animated graphics and could be upgraded eventually to 128kilobytes of memory. You started to be able to buy a lot of additions for your Spectrum that plugged into the rear connector, which allowed printers and even a hard disk to be connected. The keyboard was not special, so you could also buy a kit that allowed a better keyboard to be added to the original works by replacing the top half of the case with a much more useful set of real keys.

A more sophisticated version replaced the spectrum case entirely and you fitted the inner workings inside a 102 key keyboard.

The larger version was almost the same as PC keyboard
Pretty soon I was tinkering with the inner workings of the spectrum and fitting a reset button, a break key and re-writing the ROM to add little touches such as replacing the copyright Sinclair notice with my name. I was able to add more memory without having to buy the Sinclair kit. There was a bug in the original Spectrum ROM which could be exploited if you knew how and many off the shelf programs used this. If you knew how you could, with my added break key, halt a program in the middle and then reverse engineer the code to make your own version. This was not possible on an unadulterated Spectrum and was a little close to infringing someone’s copyright, but we did not think of those things then.

By this time the number one son had his own Spectrum and was writing programs of his own. The number two son never got into computers quite to this level, having written his own program at age eight, he lost interest in that side of it and moved on to war games.

The BBC could have a number of peripherals, such as a floppy disk drive and its own monitor.
Eventually we both upgraded to the BBC computer and tinkered with that instead. The BBC was a lot more sophisticated in many ways, although it used a less powerful processor than the Sinclair computers, it had a neat trick where you could add all sorts of extra functionality using what they called Sideways RAM and Sideways ROM. These were extra panels that you could fit inside the computer where it expanded the capabilities of the system enormously.  It had a built in keyboard and was a lot bigger than the Sinclair computers plus a great deal more expensive but fairly soon you could buy a second hand BBC for a reasonable sum.  The BBC computer was sometimes used in industry and I was amazed once when doing a tour of the local sewage works, as you do, to find they were controlling much of the waste water processing via a bank of BBC computers. The BBC was the last of our pre PC computers and by 1990 we were building our own PCs from off the shelf components and were getting into DOS and Windows. Mind you things were very different then as my first hard disk was 32Mb in size; the maximum DOS could use. It was not until I installed Windows that I could increase the disk to 100Mb and it seemed to me at the time a huge amount of storage space. When you consider that you can now get drives of six Terabytes, which is 60 thousand billion more storage, things have moved on a bit.
One of the interesting side effects of the 80s boom in home computers was that it generated a lot of software savvy computer geeks and many years later when I was teaching computer programming, we started to find a skills gap in our younger candidates. These were people who had not grown up in a house which had an 80s style home computer, but had only ever seen a PC. They had never had to learn programming and so, when they came to us, we had to start teaching them the basics at a much lower level before we could get onto the main syllabus. Something that, thanks to 80s home computers, we had not needed for many years after Sinclair introduced his home computer range. This skills gap is now being covered by the introduction of small hobbyist computers like the Raspberry Pi in schools and so school leavers may soon have caught up with the 80s generation of children.


  1. I remember the ZX81 but I never had one. My first computer was an Amstrad.

  2. Ouch, Snafu!! You left me way behind!!!! I think I'm brilliant just conquering Windows 8.