back to article 10 PRINT "ZX81 at 37" 20 GOTO 10

The ZX81 was launched 37 years ago this week as a £49.95 kit (£69.95 assembled) and introduced an entire generation to the joys of computing, fights over the family television and prodigious use of sticky tape. Intended as a successor to the ZX80 (£79.95 as a kit and £99.95 with all the soldering taken care of-ish), the ZX81 …


  1. Lotaresco Silver badge

    I remember...

    Writing a lunar landing game in Z80 Assembler then lovingly hand-coding it in hex. I worked hard to give it real-moon physics and "realistic" thrusters that displayed flashing '<' or '>' and '=" alternately to give the effect of 'flame' the sky was peppered with '.' and '*' and some of them twinkled in a completely non realistic manner.

    I loved it, friends hated it, but then having declared their hate would spend hours trying to land it before the "realistic" and almost inevitable crash happened.

    1. CrazyOldCatMan Silver badge

      Re: I remember...

      Writing a lunar landing game in Z80 Assembler then lovingly hand-coding it in hex

      We did something somewhat similar on the Nascom-1 that we had.

      Then, one day, we bought a ROM that contained Super Tiny Basic. No more hand-assembly!

      Sadly, it was very definately tiny and basic. But not so super.

      1. hplasm Silver badge

        Re: I remember...

        I printed out the ROM listing for the Nascom 1 at college*. Took a whole *roll* of printer paper.

        I was impressed by the company 'Microsoft' that wrote it, then.

        * Also ripped of an eprom copy, intending to use it on my homebrewed Z80. heh heh.

      2. John Brown (no body) Silver badge

        Re: I remember...

        "Sadly, it was very definately tiny and basic. But not so super."

        The clue is in the name. Super Tiny (very, very small), not Super BASIC (very very good):-)

    2. Oh Homer Silver badge

      Programming vs Hacking

      I remember being far more excited about PEEK and POKE than PRINT and GOTO. :)

      Actually, that's probably a serious point. Back then we were not only encouraged to program for ourselves, but we were also actively encouraged to "hack", which in my experience leads to far greater understanding of computing in general than just following textbook procedures.

      Not that I have an objection to software engineering. All Hail engineering principles! But that's only half the story. To understand how to fix things, you first need to understand how they break.

      1. Simon Harris Silver badge

        Re: Programming vs Hacking

        Back then we were not only encouraged to program for ourselves, but we were also actively encouraged to "hack"

        One difference back then were that it was possible for a person to know exactly what every chip in the computer did - ok, some like the ZX81 and BBC Micro put stuff in custom logic arrays, but at least the BBC logic arrays were well documented. I don't know how good the ZX81 manuals were for that.

        Another difference was the DIL package. Back before surface mount became common, and 0.1" was the standard pitch for things us mortals had a good chance of being able to modify the motherboard without destroying it. And back when the highest frequency you were likely to see on a computer was 4MHz you could get away with a lot of circuit hackery before RF became a problem.

        1. geekbrit

          Re: Programming vs Hacking

          One of my favorite memories of my Nascom 2 - spending a couple of hours staring at the circuit diagrams (supplied with the kit) then realizing I could route a higher frequency clock through a spare DIP switch into the cassette UART... giving me screamin' fast 4096 baud program saves & loads! Just think... a whole 400 characters per second!

          1. Simon Harris Silver badge

            Re: Programming vs Hacking "4096 baud"

            I think you'd need to do more than just change the UART baud rate.

            Wouldn't you also have to change the CUTS modulation frequency generator (it normally generated 1200/2400Hz, and I believe in the Nascom 2 was generated by dividing down a 500kHz clock using CMOS counters), or the phase would keep shifting and you wouldn't get a complete cycle for each bit?

            You'd need a 4096/8192Hz pair of signals - for comparison the MSX's 2400 baud doubled the CUTS modulation tones to 2400/4800Hz. I had an Oric-1 for a while which had a 2400 baud option, but I could never get it to work reliably. Well done if your 4096 baud worked!

  2. King Jack

    Gateway Drug

    I was too poor to afford one but my neighbour had one. I spent many hours typing away at the keyboard playing adventure games. When I got stuck I began reading the code to get the answers which proved more fun than the game itself. I mastered the 'Ram pack Wobble' which on reflection was a good thing. When the machine crashed, you had to re-input everything again. That was good practice and burned the language into your brain. They (thankfully) don't make 'em like that any more.

    1. SwizzleStick

      Re: Gateway Drug

      I had a metal bracket on to "secure" my ram pack and the fekker still wobbled from time to time.

      1. werdsmith Silver badge

        Re: Gateway Drug

        I reconditioned mine. Replaced the UHF RF TV modulator, and fitted an adapter to read SD cards. Every software title ever published for it fits on a single card. Very sentimental about it, I still remember the feeling of seeing it work for the first time, and as basic as it was - back then it was pure science fiction.

      2. Lotaresco Silver badge

        Re: Gateway Drug

        "I had a metal bracket on to "secure" my ram pack "

        I had a ribbon cable with a socket at one end and an edge connector at the other. that meant that I could use the RAM pack and any wobbling of the ZX-81 didn't cause any problems. The sockets and edge connectors were available at Maplin.

        1. Little Mouse

          Re: Gateway Drug

          I had the whole unit sat on a metal sheet with the ram pack wedged tight with a piece of garden hose. It acted as a massive heat-sink and cured the wobble - Worked a treat. The design was from one of the many magazines - can't remember which one though.

          And if you needed to copy games:


          RAND USR 836

        2. David Glasgow

          Re: Gateway Drug

          Ahhhh. Maplin. :((

      3. big_D Silver badge

        Re: Gateway Drug

        I had a Bug Byte 16K RAM Pack and I built a base for the ZX81, the Bug Byte and a Kayde keyboard (real keys, woohoo!!!).

        It stuck everything firmly on the base and it fell off my desk once and I didn't get a RAM pack wobble!

        I had a dodgy extension lead, which could send a spike that would "break" a running program, even a machine code one with, which had disabled the break key press. This allowed me to them list the machine code and I could go in and, for example, change the shape of the space ship in Defendr (not a misspelling), which in turn would make it invulnerable to crashing into anything!

        3D Monster Maze was my first experience of 3D gaming and was, for its time, amazing, considering the 32x24 display!

        1. Missing Semicolon Silver badge

          Re: Gateway Drug

          +1 for 3D Monster maze!

          1. Anonymous Coward
            Anonymous Coward

            Re: Gateway Drug

            Don't forget 3D Defender!

      4. Jedit

        Re: Gateway Drug

        The best RAM packs for the ZX81 were the dkTronics line. Instead of being a vertical box, they were shaped to fit the rear of the computer and came with a Velcro pad to secure the far end. Absolutely stable, and with larger surface area they ran cooler to boot.

        1. Peter Gathercole Silver badge

          Re: Gateway Drug

          I added an external keyboard using a Tandy membrane keyboard, suitably modified by scraping tracks and repainting with conductive paint. This was attached by a ribbon cable long enough that ZX81 and rampack was some distance from the keyboard. Never had a wobbly rampack crash after that.

          I also added a 7400 TTL on a small board in the Sinclair rampack to re-map the 1K of static memory to a usable memory address (which I used for small machine code assists to basic), and also added another 1K of static memory under the keyboard, attached to the ULA side of the bus isolation resistors. This allowed me to change the I register, which was used to hold the base address of the character generator table to point at an address in this RAM. This gave me a fully programmable character set! So my ZX81 was probably the only one with 18K of RAM!

          I also had a sound board from QuickSilver which provided 4 channel (3+white noise) sound using an AY-8910 sound generator added to the video signal using an external modulator. QuickSilver also produced a point addressable graphics board, but I think that worked by doing a similar trick to mine with the RAM, and writing all the characters out to the screen, and manipulating the pixels in each character cell. I believe that it came with some M/C routines in an additional ROM that allowed basic line draw commands.

          I had great fun getting it to produce harmonized music while drawing it on the screen at the same time. The only problem was that in 'slow' mode, the Basic was just a bit too slow to make it seamless.

          Although it looked a bit Heath-Robinson, it drew some interest in the computer club of which I was a member.

          1. John Brown (no body) Silver badge

            Re: Gateway Drug


            That was a very nice, user friendly sound chip in the day. It even had one (or two?) 8 bit user ports to control further device. I knocked up a few little circuits based on various "gunshot" type sound circuits to simulate a few drum sounds which left the "proper" audio channels for the music. I was well proud of that at the time!

        2. Danny 4

          Re: Gateway Drug

          dkTronics Rampack

          I had a Memotech 16K Rampack. Seems they used the same solution of velcroing a shaped metal-cased rampack to the back of the '81. Very stable and ran cool.

          Adding memory was the only way to make the ZX81 usable. Much like a the 16K vs 48K Spectrum.

          1. Jedit

            "I had a Memotech 16K Rampack. Seems they used the same solution"

            Assuming I'm not misremembering the name after 35 years and we're not talking about the same peripheral: it's quite likely they used the same blueprint for the external shell, if not the same manufacturer.

      5. Pen-y-gors Silver badge

        Re: Gateway Drug

        Ram Pack Wobble - bent coat hanger that clamped it into place.

        And don't forget the pack of frozen peas on top when it overheated and died.

        1. werdsmith Silver badge

          Re: Gateway Drug

          Two blobs of blu-tack fixed the wobble for me.

  3. Anonymous Coward
    Anonymous Coward

    One of our mainframe engineers bought one and asked me for some assistance in programming it. IIRC the 16K expansion pack used to get very hot.

    I had an Apple][ bought in 1979. For comparison with the ZX under-£100 prices - that had cost about £1800 with black&white video, 48KB of ram, and an Apple format floppy disk drive.

    To get down to the lower prices before the ZX you had to build your own - like the "Tangerine".

    About that time there was an explosion in PC magazines, exhibitions, and specialist shops. At one of the exhibitions we drooled over an Apple compatible Winchester hard disk of 10MB - priced at £2K (about £6K in 2018?).

    1. I ain't Spartacus Gold badge

      Yes, I remember those RAM packs - and they got very toasty warm. As well as being wobbly.

      I'm deeply insulted by the comment about only simple games. I remember playing a whole Harrier Jumpjet simulator. The graphics were amazing.

      1. PaulyV

        Computer exhibitions and shows - that takes me back. Being driven out by my Dad to hotels in places like Huddersfield or Grimsby, parking up and being directed to the conference suite. Desk after desk of Vic20's, Oric 1's and Dragon 32's were setup, each accompanied by a chap more than happy to talk about them at length. The BBC B's felt like the best built and eventually our primary school got one, whilst at home my parents splashed out god knows how much on a Dragon 32 which saw me through my youth.

        Never had a ZX81, but Dad did borrow an '80 for a week or two from one of his younger colleagues. I still recall tuning it in to the TV.

        1. Just Enough

          I have the afternoon I spent coding a borrowed ZX80 positively seared into my memory. Plugged into the TV. Tuning the TV to the right frequency. Lying on the carpet. The slightly burny smell of the components as they heated up. I started with a printout from somewhere, but soon went my own way, coding the animation of a graphic square bouncing across the screen, then "exploding" in the corner.

          I used a ZX81 not long after that, and of course a Spectrum. But no exaggeration to say that ZX80 was a defining moment in my life.

          1. mrdalliard
            Thumb Up


            Wonderful stuff. At the age of ten, my parents bought me a ZX-81 and I spent countless hours using it. My poor black and white TV got completely ruined in the end by "burn-in". Watching regular TV programmes got quite hard (as the picture got fuzzy) and images/listings that I left on the screen for too long ended up getting burnt in to regular viewing.

            I went from the ZX-81 to a Vic-20, which seemed a novel thing as it had sound, colour, a larger memory and a fairly reliable dedicated tape drive.

            I never looked back - I've been in IT most of my working life.

            1. I ain't Spartacus Gold badge

              Re: Burn-In

              I went from the ZX-81 to a Vic-20

              My mate's Dad had bought a ZX81 to play around with. But my older brothers pooled some birthday money to get a Vic-20 - so that was my first real experience of regular computing. Their next was an Amstrad CPC464. Happy days.

              The great thing about the Vic-20 was you could get some games in cartridge form and just plug them into the back, so you didn't have to wait for tape loading. Luxury!

            2. Anonymous Coward
              Anonymous Coward

              Re: Burn-In

              "I went from the ZX-81 to a Vic-20, which seemed a novel thing as it had sound, colour, a larger memory and a fairly reliable dedicated tape drive.

              I never looked back - I've been in IT most of my working life."

              That was me too.

              ZX81 -> Vic20 -> Spectrum -> Amiga -> PC -> Career in IT

              1. darklord

                Re: Burn-In

                for me

                ZX80>ZX81>BBC MOD B> COMMORE pet> AMSTRAD CPC464>SPRECTRUM> PC8088>PC8086>ATARI ST>286 onwards to a career in IT and there was an Osbourne in there somewhere.

              2. Anonymous Coward
                Anonymous Coward

                Re: Burn-In

                Similar path for me:

                ZX81 > Spectrum > Amstrad CPC6128 > IBM XT > Career in ICT

        2. Wayland Bronze badge

          The Dragon 32 was good for programming. The BASIC was fine and with an Assembler and text editor the 6809 was much nicer than Z80 or 6502. The only problem was no sound chip and poor video chip. If it had a couple of chips out of the BBC B it would have beaten it. Half the price at £200.

      2. CrazyOldCatMan Silver badge

        The graphics were amazing..

        .. for their time. I fired up a BBC B emulator recently to play some of the old games and got bored very quickly. Likewise with an Atari ST emulator.

        1. John Brown (no body) Silver badge

          ".. for their time. I fired up a BBC B emulator recently to play some of the old games and got bored very quickly. Likewise with an Atari ST emulator."

          Your imagination has died with age. Gameplay was often very, very good (lots of dross too!), but you really needed imagination to "see" what was going on. I wonder how many old farts here can "see" a cardboard box as a spaceship, a racing car, a train, a TARDIS etc and spend hours playing in it? I bet any 5 year old relatives you might have can do it.

          1. Dave K Silver badge

            "Your imagination has died with age."

            Agreed. I'm a bit too young for the ZX81, I cut my teeth on the BBC. Games like Repton 3, Pac Man, Defender and of course Elite are still fun today, and really show just how much you can get out of these machines with some clever programming!

          2. Anonymous Coward
            Anonymous Coward

            Sam Fox Strip Poker on the Spectrum - 99% imagination.

    2. Ian Michael Gumby Silver badge


      There was only one real computer magazine at that time (BYTE).

      Yeah, lots of toys... unfortunately we fried our boards when we were soldering in the PS cabling.

      (It was a cheap learning experience...)

      If we wanted a computer game... we had to write our own. Today.... kids just go online, or just buy it.

      How many people remember "Hello Sailor" ? ;-)

      Mine's the jacket with the HP RPN calculator in his pocket.

      1. Anonymous Coward
        Anonymous Coward

        Re: Memories...

        "Mine's the jacket with the HP RPN calculator in his pocket."

        Mine's the HP "Programmer" from 1978 that did octal and hex calculations - with binary shifts and XORs too.

      2. Peter Gathercole Silver badge

        Re: Memories... @IMG

        I'll see your HP RPN calculator (mine was an HP-45), and raise you (because of difficulty in fitting anything useful in the limited memory) a Sinclair Cambridge Programmable and a Commodore PR-100 (I also had a Texas TI-57 programmable at one time, but it went wrong after about 2 weeks, and I got my money back).

        I've forgotten all of the other calculators I've had across the years. I still have a TI-58 as an ultimate fallback, but I mainly use my 'phone now.

        Interestingly enough, in the past couple of weeks, I've had to remind a colleague about the fact that some calculators did arithmetic hierarchy (generally TI and possibly Rockwell), and some didn't (Sharp, Commodore/CBM, early Casio, and most cheap 4/5 function calculators). HP were pretty much a law unto themselves, using RPN.

        1. travellingman_us

          Re: Memories... @IMG

          I had the first Sinclair programmable calculator... that I bought with money from my first after school job!

          My math teacher & I had great fun writing programs to do all sorts of fun (but otherwise) boring things. It was so "revolutionary" it was actually allowed into my math higher exam -- calculators were allowed, and no-one had thought to restrict programmables yet!

          Helped me get a few, otherwise dodgy, points in some areas!

          1. Peter Gathercole Silver badge

            Re: Memories... @travellingman

            I'm really not sure how much of an asset the Cambridge Programmable would have been in an exam over a normal scientific calculator.

            It did not have any stored memory capability, so you would either take it in powered on, and risk the battery running out, or remember any program that you wanted to use, not that much of a problem, however, with only 32 (or was it 36) programmable steps.

            I did use a high-function Commadore SR4190R in a physics exam at university to do some linear regression that I could not remember the formula for. Worked out the results, then reverse-engineered the calculations to fit so I could present my 'workings'. Non-programmable scientific calculators were allowed, but I suppose it was cheating (a bit). I don't actually think that that exam added much to my overall degree.

        2. Mark 56

          Re: Memories... @IMG

          Mine's the one with the SwissMicros DM41L

        3. Ian Michael Gumby Silver badge

          @Peter G. Re: Memories... @IMG

          If memory serves... mine had LEDs and I forget the model. We're going back over 40 yrs.

          Why play with a calculator when you had computers. ;-)

        4. AndyD 8-)&#8377;

          Re: Memories... @IMG

          "HP were pretty much a law unto themselves, using RPN."

          as did Sinclair's

    3. dmackenziephoto


      I built a Tangerine computer. I even had the rack mount for it and it's peripherals. Originally programmed via the hex keypad I graduated to a proper keyboard and the Basic ROM. Wonderful. I understood everything the 6502 CPU, and the serial chips could do. Loved it

  4. Geronimo!

    "Syntax error in line ..."

    "Magazines would publish reams of code to be laboriously entered before the user could spend a few happy hours playing "hunt the bug/misprint" and then be intensely disappointed with the results."

    1. Anonymous South African Coward Silver badge

      Re: "Syntax error in line ..."

      Some magazines (later on) used to have a checksumming utility with which you input a line of code, then it gives you a checksum on completion of that line, which you then compared to the one in the magazine listing. If it compares, you continue on with the next line, if it doesn't, you re-input the entire line.

      Especially when having to input machine code stuff. Which tend to crash spectacularly should you get just one line wrong.

      1. Anonymous Coward
        Anonymous Coward

        Re: "Syntax error in line ..."

        "Especially when having to input machine code stuff. Which tend to crash spectacularly should you get just one line wrong."

        That has always been true of most computer languages. You can't lie to a computer.

        The alternative to the crash is the subtle bug that only shows up on certain occasions. It is not unusual for a bug after an enhancement to actually be a mistake that had been there for years.

        A new version of the established O/S was built for the latest model's prototype. There were two other mainframe models which were already being sold with the same O/S. After working OK on the prototype for several weeks - it suddenly started crashing.

        It turned out that an established code path did a bit test on totally the wrong address. The outcome of the test in the past had always sent it down a well worn path - and the alternative possibility had never been expected or tested.

        The crucial difference was that the name of the O/S file had now finally been changed - in only one character - to reflect the different mainframe model.

        The file name was also stored in memory after loading. That single character's address was coincidentally the one being mistakenly tested. The previous two mainframe models just happened to have a consistent setting of the bit in that character in the file name - the new name had changed the tested bit.


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