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. Little Mouse


      I just recited the Clown/Ring-Master's "Roll up, roll up" intro to myself. Verbatim.

      It's still stored away up there, unlike much of the French, Shakespeare, etc that I was actually trying to memorise at the time...

  1. Potemkine! Silver badge

    Ah, memories...

    The 16KB extension was a PITA because of its frequent disconnections when the computer was accidentally moved, as was the tape recorder way to save and load programs...

    Nonetheless, we spent many hours as teenagers with a friend on our ZX-81s learning BASIC first and Assembler programming next, many hours of fun and wonder discovering programming. Not surprisingly, we both became developers in the following years. Thanks ZX-81, you little box enabled us for a reasonable price to discover a new World! I still have you preciously stored in a drawer, next to my beloved ATARI-2600.

    1. Ryan Clark

      Re: Ah, memories...

      My main memory was spending a considerable amount of time typing out the code from a magazine before my brother knocked the desk set up in front of the TV and it reset and I had to start again. Don't actually remember playing games or the code, just the annoyances.

  2. Zog_but_not_the_first Silver badge
    Thumb Up


    ...a minor cascade of loving tributes to this brilliant little machine.

    Feel free to add mine.

  3. Christian Berger Silver badge

    I have a ZX80 with the ZX81 upgrade

    So I didn't have the "slow mode".

    Using tokens to store BASIC code wasn't uncommon back then, as it not only reduced the memory footprint, but also gave you faster BASIC execution.

    Such low end home computers also nicely show where the line between a "single purpose" computer and a real universal one lies.

    1. Simon Harris Silver badge

      Re: I have a ZX80 with the ZX81 upgrade

      Using tokens to store keywords was quite common on many computers back then, but the tokens were usually expanded to keywords only when the LIST command was used.

      On the ZX80/81 the tokenised keywords were displayed in full even from within a program if you had a line PRINT CHR$( x ) where x corresponded to the value of a keyword token. Using PRINT CHR$( x ) on most computers would normally display a single character or some screen control action such as clear screen or cursor movement.

  4. Outer mongolian custard monster from outer space (honest)

    I had one, well a couple after accidents with shorts and electrical issues, 1k at first, then the infamous sinclair ram pack. Cured wobbly ram pack crashes by gluing zx81 and rampack solidly to a formica board, end of crashes.

    Also decided to get a bit experimental, built my own full size keyboard from a recycled industrial keyboard from the "Computer Junk Shop" in wallasey (magic emporium) which at the time was jammed full of weird stuff and PETS and decomissioned mini's amongst other wonders and learnt about keyboard matrix's etc. Also added a extra chip piggybacked on the char rom, and this meant that the ascii charset got shunted into ram and could be edited for customisable graphics!

    Also remember the wonderful "Buzz" organ, which drew bands onto a CRT tv causing it to hum loudly with the abuse. Different keys produced different band frequencies, which caused different tones of hum, voila a organ on a machine with no sound hardware.

    For tapes we found a certain brand of small tape deck was perfectly matched, and I still have one today (it was a sharp, I'd have to go dig it out as my zx81 today is a display cabinet thing rather than in actual use, and its original not sprouting hook up wire out of every melted in hole in its casing like my real one was)

    Did the writing stuff in z80, then encoding it into hex, then ascii, and storing it as a load of REM statements and jmp into it to run like another poster above. Tedious but fun to learn and do. It was just what you did back in those days wasn't it? I think it was fantastic and I really pity a youngster of today trying to try and understand the innards of a x64 apu based black box system to the same level we were able to read and understand that simple little 8 bitter. I showed my son zx81 basic and helped him write the classic hello world goto 10 3 liner in it on the actual computer and he got it straight away, so still some value in simplicity.

    Also have the cushions in my gamesroom with mazogs on them, ascii graphics being perfectly suited to replication in patchwork designs, also in tiling, although the floor has a giant space invader tiled in, as my wife said mazogs would be a bit too obscure if we ever sold the house :D

    Nostalgia, still, glad time and performance has moved on, and the original keyboard is still bloody awful even today.

    1. CrazyOldCatMan Silver badge

      Also remember the wonderful "Buzz" organ, which drew bands onto a CRT tv causing it to hum loudly with the abuse

      I remember trying to make music using the 'polyphonic' sound chip on the BBC B. Was very proud of the 'song' I made.

      Trouble was, when I came to ask my friend to add a guitar over the top (using his advanced 4-track tape mixer) we discovered that the tones used by the BBC were nothing like correct in pitch.. So, even though the song was supposed to be in C, in actuality it wasn't.

      So, of course, I blamed the computer rather than my musical skills. What else are computers for?

    2. Anonymous Coward
      Anonymous Coward

      Minimalist Electro on the ZX81 (and why programming an x86 isn't)

      "Also remember the wonderful "Buzz" organ, which drew bands onto a CRT tv causing it to hum loudly with the abuse. Different keys produced different band frequencies"

      I did that too! Found a program in my Dad's old "Sinclair Programs" magazine that- IIRC- toggled between FAST and SLOW modes producing an audible buzzing then experimented myself with delays and other effects (repeatedly sending a COPY to the printer when there was no printer attached also made noise IIRC.)

      There might still be a tape of 10-year-old me singing nonsensical- and frankly strange- lyrics alongside the alleged "music" I made this way. It'd probably be hailed as a minimalist Kraftwerk/Numan-influenced electro masterpiece nowadays. (#)

      Also, you can- in theory- still program an x86 based computer using assembler, but it's worth remembering that since the Pentium Pro and Pentium II came out, all recent Intel processors (and presumably AMD by now) use a completely different internal microarchitecture and instruction set.

      Some have described this instruction set as RISC-like, though others dispute that (##)- regardless, the important part is that it's *not* x86. The x86 instructions are converted on the fly via a decoder into the native format, so even any "native" x86 code you write is still effectively being run under emulation by a completely different architecture anyway!

      (#) It wasn't, I preferred ABBA, even though this was 1986 and they, Numan, Kraftwerk and the ZX81 were all passe by this point. I got an Atari 800XL soon after this...

      (##) Since this internal instruction set isn't- AFAIK- exposed or available for regular programming use, there's nothing stopping them from completely changing its design to suit themselves anyway; all that has to change is the x86 emulation "API".

  5. Nugry Horace

    15 SCROLL

    Otherwise the program will stop with error 5 when it reaches the bottom of the screen.

  6. James Cullingham

    Every byte counted

    My 'favourite' feature related to the storage of numeric constants that formed part of a line of BASIC. As background, you have to bear in mind that the machine was very storage constrained, but also very performance-constrained, especially when it came to FP arithmetic.

    Say, for example, you had a line

    10 LET A=1

    10, as the line number, was stored in 2 bytes

    LET was a keyword, so was stored as a single byte token

    A and = obviously took 1 byte each

    But then came the numeric constant 1. Due to the performance hit of parsing that into an 5 byte FP representation (1 byte exponent, 4 byte mantissa), this was done as the line was entered, so what actually ended up in memory was the code for the character 1, followed by the marker byte 0x7E, followed by 5 more bytes of data.

    Horror! One character took 7 bytes!

    It was actually more efficient to write instead

    10 LET A=PI/PI

    because PI was, again, a single byte tokenised keyword, so now you had 3 bytes instead of 7 - a substantial saving and one that would add up over the length of a full program.

    Similarly 3 was INT(PI), and arbitrary constants were, IIRC e.g. INT("12345") (still saving 3 bytes).

    You got the performance back by writing every-increasing amounts in machine code (process: write it out, then hand-assemble, then create a hex entry utility, then type in the entire codebase in hex)

    And you saved bytes in your machine code by referring to your disassembly of the entire ROM (published as a book -,%20O%27Hara%29.html) to see if you could abything from a full routine down to a few bytes here and there.

    Happy days!

  7. WozNZ

    10 PRINT "Hell

    arrgh bloody ram pack wobble

    10 PRINT "Hell

    oh ffs, again. really

    Place I cut my first code :)

  8. Soul assassin

    3d monster maze!!! Scariest game in creation!!! :)

    1. Michael Strorm


  9. Hockney

    3D Monster Maze

    The best computer game ever.

    Okay, it was all in your imagination, but it had a maze. And a dinosaur. You ran until you died.

    Perfect life lesson

    1. Anonymous South African Coward Silver badge

      Re: 3D Monster Maze

      Precursor to Wolfenstein and DOOM...

      1. deshepherd

        Re: 3D Monster Maze

        ... and looks like a sucessor of Minotaur for Acorn Atom - which according to the interwebs is a game wot I wrote. I worked at Acorn in the year before University and I think this was one of the items I ended up as author because I was the last person to work on them. Think on this I took what was an exisitng 3d maze program and added the "move the gold bars to the safe while being chased by the minotaur" bit. Anyway, it appears I may need to add "inventor of the 3D FPS game genre" to my CV!

        1. Simon Harris Silver badge

          Re: 3D Monster Maze

          Have an upvote - I remember playing that one!

          Back in those days I reviewed a few Atom games for Computer and Video Games - it's quite likely I reviewed that one.

  10. jrd


    First, type in 1 REM followed by 620 zeroes...

    --- on a keyboard with no repeat where the screen redraw takes a measurable amount of time and happens after each keypress...

    1. Anonymous South African Coward Silver badge

      Re: Nostalgia

      Why would you want to do that? :)

      1. GrumpenKraut Silver badge

        Re: Nostalgia

        > Why would you want to do that? :)

        To fill it up with machine code?

        1. jrd

          Re: Nostalgia

          Correct. You'd then write a small loader program which would allow you to enter hex machine code into the REM statement. You couldn't safely load machine code directly into memory as this would be cleared automatically when you typed RUN so hiding it in a REM statement was a common trick.

    2. ThomH Silver badge

      Re: Nostalgia

      Now do it on a ZX80 where each keypress is followed by a screen bounce as the CRT tries to resynchronise with a video signal that momentarily went missing. The ZX81's constant display is virtually space age!

  11. OldPalmFan

    I designed a bridge on my girlfriends' ZX81

    I was a Royal Engineer officer and had a task to build a wooden foot-bridge at a National Trust property. The design process was iterative; you guessed some dimensions, ran them through the calculations in the Improvised Bridge Design manual to see if the bridge was strong enough and if not could see what bits needed to be bigger (keeping it simple for you Register types). Perfect for a computer programme, I thought and my girlfriend had 'a computer' a ZX81 complete with wobble-pack. So I wrote a programme that worked through the iterative steps and ended up with a design. Somewhat proud of this I listed the programme in my design report CO completely po-poohed the idea of using a computer and thought it ridiculous that they could ever be of any use in RE tasks. A visionary he was not. After I left the Army I moved into IT where I've been for the last 25+ years (but not programming, I'm rubbish at it but the bridge was built and didn't fall down!).

  12. roger 8

    I had the zx81 my mate had a spectrum. Born in 69 was the right time. by the mid 80s when I was in comprehensive school we had Commodore PET and BBC B micro and a little bot with a pen. I think the program was called LOGO. pen up move 10 right 90 pen down move 10. I remember me and a friend drawing out the full map for manic miner on graph paper and sticking it to the wall. it was a big map. I remember my dad coming home from work wtht a parcel and gave it to me. said the IT guy from head office had brought it ( dad worked for Ciba-Geigy at the time.) it was a massive printout of a game. on green and white listing paper. looked like something from nasa. took me ages to type it all in and save it to audio tape

    1. dc_m

      it's called mslogo now.

      The "little bots" are known as turtles, they are still being used. There are variations of basically the same thing.

      It would have been a variant of the original valiant roamer. Uses two massive lantern batteries. I know for a fact schools were buying these no more than 8 years ago.

  13. Ian 45

    Yup my first

    With 16K ram pack!

    1. salamamba too

      Re: Yup my first

      My first computer as well, but with a 64k japanese ram pack that negated the warranty of the computer the moment you used it.

      Always fun when speccie users boasted about their 48k.

  14. fixit_f

    My school had a dedicated computer room with about 12 of these, and we’d have lessons where we worked on them in pairs. The teacher would line everyone up outside with no shoes on and then get each pair of kids to creep in and sit down as slowly as possible – any more people moving at a time and there was a good chance the expansion packs would move in several of them and they’d re-set, causing whatever program we were looking at to need to be reloaded from tape.

  15. jms222

    BBC Basic

    At the museum I really enjoy watching people of _all_ ages pick up BBC User Guide or our booklet and start playing. The biggest issue is that BBC Basic is uppercase. "Mistake" doesn't quite convey this.

    Ah Ciba-Geigy. I did a contract at a related company Techne in Duxford not that along ago working on Motorola 68HC code continuing my largely 8 bit career that started with the Z80. We used their canteen and would wander onto their site at lunchtime.

    1. Simon Harris Silver badge

      Re: BBC Basic

      "The biggest issue is that BBC Basic is uppercase"

      Back then I think almost all BASIC was upper case - at the beginning of the home-computer explosion it was quite a luxury if your computer could even display lower case.

      1. deshepherd

        Re: BBC Basic

        I suspect upper case may have been a BBC requirement as they wanted it to look like other Basic's of the day.Had it not been for then I think "Acorn Basic" was going to ditch line numbers and use labels which would only be needed for GOTO/GOSUB targets.

      2. Christian Berger Silver badge

        One has to be fair

        Lower case letters were only invented in 765.

  16. Anonymous Coward
    Anonymous Coward

    Over 40 and used one of these?

    nope. Not a chance. I got burned off of anything with a 'Sinclair' label on it with his Radios. Useless POS. Components were 'engineered' out to reduce cost which had a byproduct of reducing reliability.

    As for the Sinclair 'Digital Watch'... sigh.

    As I was working for a Computer Manufacturer at the time I had big boys toys to play with at work. 32bit Multi-User Operating Systems and 256Mb Disk drives that could be made to dance over the floor. As a result I never felt the need to get involved with any of this stuff.

    1. Anonymous Coward
      Anonymous Coward

      Re: Over 40 and used one of these?

      Not sure why the down votes for my fellow commentator above, the comment has merit. Having spent the last 5 years researching many of "Uncle Clives" firms and having collected one of each of most of his companies devices, many of them were frankly crap. Sorry. Some were design classics such as the Neoteric or the Forum Phone, but others, while pretty to look at, just didn't work eg, the Black Watch or Stereo 60

      Too many people seem to have a very rose tinted view on his work. While he may have brought many technologies into to home or workplace due to "at the time" great prices and a bit of style, many were just not as good as many of the competitors at the time.

      anonymously - I don't want to f*** up any chances for my forthcoming book........

      1. Anonymous Coward
        Anonymous Coward

        Re: Over 40 and used one of these?

        Think it might have been the "I worked in a job where I got access to whizz bang fancy computers, so I'm alright Jack" attitude as well.

        "As a result I never felt the need to get involved with any of this stuff."

        Yeah, good for him/her being lucky enough to be able to look down their nose at it in the first place. Not everyone- well, let's be blunt, not many people- would have been in jobs where they already had access to all those "big boys toys".

        I for one didn't, possibly because I was six years old at the time.

        Don't think anyone was under the impression that the ZX81 was the powerful leading edge of even home technology at the time. The Atari 800 (for example) was light years ahead... on the other hand, it would have cost- AFAIK- approaching ten times the price of the ZX81 on the UK market. Which is pretty much the bloody point- most people wouldn't have been able to afford an Atari 800 or Apple II, but the ZX81 was affordable.

        The blunt truth is that the ZX81 was the first opportunity many people would have had to play with a computer of their own (or their first experience of a computer full stop). Most of its limitations and idiosyncracies- bad RAM pack design excluded- could be forgiven on this basis, even if it was superseded by better machines fairly quickly. (Not least by Sinclair's own Spectrum, which was far from perfect either, but still the first computer at that price capable of hi-res colour graphics that could passably approximate arcade games; maybe less so in the "sound" department, though...)

      2. Andy3

        Re: Over 40 and used one of these?

        Hmm. I grew up making Sinclair kits and every one of them worked. The little radios (I had a Micromatic) worked fine and My stereo record player used two Z30's and a Stereo 60 pre-amp unit. All fine and lasted years. We even made an amplifier for our mobile disco using two Z50's and a PZ8. This may sound like a recipe for disgruntled dancers, but it only ever went off once - and it came back perfectly after a reset. I honestly think many of the complaints about Sinclair stuff come from people who built it badly.

    2. Phil O'Sophical Silver badge

      Re: Over 40 and used one of these?

      I got burned off of anything with a 'Sinclair' label on it with his Radios. Useless POS.

      Not everything. My original Sinclair Scientific still works, RPN logic & all!

      1. Andy3

        Re: Over 40 and used one of these?

        And I still have my (working) Cambridge calculator which I bought in 1974 (I think).

    3. Alister Silver badge

      Re: Over 40 and used one of these?

      I bought the Zylog Z80 Programming Manual, with MY OWN money, on the strength of having a ZX81, and taught myself assembler.

      Unfortunately, when I started college 6 months later, all the Computing courses were done on Rockwell AIM65 machines, so I had to start again...

  17. MikeCorris

    My friend had a ZX81 for his birthday. I remember we used to lie on the floor in front of the telly laboriously typing as previously mentioned. When the 16K RAM pack came out we couldn’t imagaine anyone needing 16K! Eventually he got one of course and ram pack wobble became our nemesis. I got a 16K Spectrum some time later. After having that for a while it got sent away too have the 48k upgrade for my birthday. It arrived before my birthday but I was told not to play any 48K games until my birthday! Can’t believe it looking back but my mate got me a copy of manic miner and we used to play it secretly when my dad wasn’t there! Those were the days...

  18. AS1

    No wobbling here

    Never had a problem with RAM pack wobble; maybe I received the only Sinclair pack with a good connector, or maybe because I plugged in the pack once, and never removed it. It even survived being dropped a couple of inches while running a Nightfall clone at the local CUG held in a function room over the local (see icon, for the parents of course).

    I miss the manual; everything nowadays is so poorly documented and seems to rely on users helping one another. Cheap but inefficient.

  19. Anonymous Coward
    Anonymous Coward

    Ah, the memories. Excuse me while I find the bleach...

    My first computer, and the reason I learned Z80 machine code (lddr made for some interesting scrolling games...). Made my own joystick, attempted to make my own RAM pack...

    Also the gateway to a long career in IT. Very few regrets.

  20. DJO Silver badge


    Then as a reader of Wireless World I thought the ZX series was for kiddies so when WW published a design ( I saved up my pennies and built one, oh the fun of soldering 5k of 1 kilobit chips (with parity) that's 45 x 20 pin chips and then actually getting the bugger to work was a great source of joy (for "joy" read "frustration").

    But once it did work it was an interesting machine boasting a calculator chip as a "maths co-processor" which allowed far more complex programs and a novel version of BASIC using reverse polish notation which had the great advantage of confusing the hell out of almost everybody who saw it.

    Learned a lot about computer hardware and how to do terse programming, a skill that seems to have been lost now as memory and storage are cheap and abundant.

  21. Ken 16 Silver badge

    I had a ZX80

    because it got discounted when the ZX81 came out

    I spent hours typing games into it and never getting them to load from tape successfully after.

    I bought an ICL OPD when I was in college (spectrum with knobs on).

    Never follow my example when buying any technology.

    1. Lotaresco

      Re: I had a ZX80

      "I bought an ICL OPD when I was in college (spectrum with knobs on)."

      Errm the OPD was a Sinclair QL with a built-in telephone handset. The similar device that was a Spectrum with knobs on was the Amstrad emailer.

      1. Anonymous Coward
        Anonymous Coward

        Re: I had a ZX80

        IIRC the Amstrad Emailer had nostalgia-exploiting Spectrum games available- presumably via emulation- but I don't think the machine itself was a "Spectrum with knobs on" either.

        1. Uncle Slacky Silver badge

          Re: I had a ZX80

          I think maybe the SAM Coupé might qualify as a "Spectrum with knobs on", failing that, the TS 2068?

          1. ThomH Silver badge

            Re: I had a ZX80

            The SAM Coupé is a "Spectrum with Prince of Persia on (and not much else)", and I loved mine dearly.

    2. Anonymous Coward
      Anonymous Coward

      Re: I had a ZX80

      Both ZX80 and OPD worth a fair bit if you kept them, so maybe not such bad choices.

      I bought a Jupiter Ace. Look how much they are worth now.

      I continue to regret binning mine when I couldn't after all get on with Forth


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