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. LeeH

    Thank You Mr Chester...

    My primary school teacher brought his ZX80 into class so we could use it during breaks. Someone broke in and nicked it over a weekend. He replaced it with a ZX81 a few weeks later. Someone nicked that as well. The 3rd one stayed.

    Mazehogs and Bomber were the games we played. Vague recollection of 3D Monster Maze. I didn't play often but fond memories made. Good times.

    Girls in the class showed no interest in it but I do remember Mr Chester showing a few female teachers his new toy; they were interested.

    Thank you Mr Dick Chester for sharing your computer with us.

    1. andyp-random-number

      Re: Thank You Mr Chester...

      "3D Monster Maze"

      ...that scared me...I wasn't ever ready for the monster!

      1. LeeH

        Re: Thank You Mr Chester...

        I was going to do some work this evening but think I'll wake up an emulator and battle monsters instead.

    2. Dan 55 Silver badge

      Re: Thank You Mr Chester...

      Admit it, his name was Richard, but you all called him Dick...

      1. LeeH

        Re: Thank You Mr Chester...

        Only one lad in the class did. The rest of us called him sir. He was one of the most liked teachers in the school. Was not funny when I hit him in his eye as he picked me up off a table in a drama lesson.

        He had told me off for being naughty a few days before and made me stand against a wall in the playground so I told the other lad stood with me that I was "going to beat him [Mr Chester] up". Well, when he pick me up off the table I thought he was starting. I would have been 9 years old. Poor bloke. He was my teacher that year so we had to patch up.

  2. Kimo

    Knew a kid who had one. Me and the other TI99 owners in my school would make sympathetic noises when he showed it off, then laugh behind his back.

  3. Individual #6/42

    My tuppence

    My First: computer, introduction to machine code (there weren't any assemblers that I knew of) and lessons in ram management (PI-PI took up fewer bytes than 0) and counting chip cycles for alternative instruction combinations. Who counts chip cycles nowadays?

    I managed to fill 16k with a reverse engineered (and enhanced) RM 380Z Star Trek exploration and combat program typed out and debugged over weeks. I had never had any trouble with the RAM pack once I'd used milliput to fix the design. Happy memories.

    1. Boris the Cockroach Silver badge

      Re: My tuppence


      Who counts chip cycles nowadays?

      That was the bane of my 8 bit programming life (after getting sick of rampack wobbles and tapes failing to load that is)

      Having a loverly set of interupt controlled animation and sound routines for a game I designed go TITSUP whenever I enabled the sound.... turned out the processing time for all the interupts was about 3 lines too long and failed to exit the interupt routines before the next interupt arrived.

      Took ages to figure out which part took too long and rewrite into something a bit smaller

      Still got my spectrum sitting in the desk next to me(no PSU though), a MTX 500, and an atari ST(heavily modded) too... one day I'll get around to throwing them all out...

      1. deshepherd

        Re: My tuppence

        "Who counts chip cycles nowadays?"

        Well, us proicessor designers are sadly still obsessed by the number of cycles in a Dhrystone loop

      2. Simon Harris Silver badge

        Re: My tuppence - counting cycles

        You can still have all that fun programming a PIC in assembly code.

  4. x 7

    I still have one, not been used in 40 years so dunno if it still works. Original packaging long since gone, but fairly certain the cables and power unit are still around somewhere

    Any museum out there want it?

    1. steviebuk Silver badge

      Ask they might take it.

  5. John70

    The first time I programmed a computer was on the ZX81 and it was a security routine. I did it because I saw a game on a Vic20 at school asking for a password and was fasinated by it.

    10 Print "Enter Password"

    20 Input A$

    30 If A$ <> "password" Then GoTo 10

    40 Rem Do Something

  6. adam eyeball

    Still have one on my desk

    I still have one on my desk at work - I saved an analogue TV so that I can show my students what computing was like in my day. It's the pity I can't handle.

    (See your RPN calculator and raise you a slide rule)

  7. John Brown (no body) Silver badge

    Slow news day?

    I still enjoyed reading and contributing to the comments, but a 37 year anniversary? Didn't we do this at 35? And will do it again at 40?

    Surely there a list 8-bit micro launch dates somewhere and we can do many more of these. No matter the make/model, there will be readers here who owned one.

    1. Anonymous Coward
      Anonymous Coward

      Re: Slow news day?

      ... well it is its silver anniversary in hex!

  8. Deltics

    My first step in a journey of 1,00 miles...

    I remember my dad taking me to the local sorting office 37 years ago to collect the parcel from Sinclair, a shiny (well, actually no) new ZX81. One of the pre-assembled ones. I imagine this is why I ended up in software rather than hardware - no soldering required. I never could get the damned thing to load anything from tape, so I had to bash in listings from magazines, and then from that took the step to figuring out that by understanding this "gibberish" I could then change those games and make them do what I wanted.

    And so began my life as a self-taught software developer.

    My own personal computing history then went down a slightly esoteric route. While most of my friends had Speccies or Breadbins (C64's), with a couple of Electron's and even one Dragon32, my upgrade path took me to a TI-99/4a since a lot of my family (large number of aunts and uncles) not to mention my own parents at an earlier time, worked for Texas Instruments. When they pulled out of the home computing market staff they sold off stock to employees at bargain basement prices. Idiosynchratic as it was, it was a damned fine machine.

    My path then returned to a more conventional route, with an Amiga 500 and after teaching myself C and Pascal programming with the multitasking GUI OS I then landed a job building software for this new fangled "Windows" on PC's which seemed positively antique compared to the Amiga (this was before even Windows 3.0).

    Thus began a career in computing and software, all thanks to my late dad and that ZX81.

    I've recently started assembling a museum of that personal computing history (the original equipment having been on-sold or disposed of, sadly not being appreciated at the time for the future value - sentimental or otherwise - that it would hold).

    The one exception being my original ZX81, but that hasn't actually worked since the late 80's. But I have now replaced it with one from ebay in near-mint condition, including original box and sleeve.

    There's something magical about switching on these old machines and seeing them spring to life as eager to please as ever, oblivious to the passing of time that has rendered them obsolete as anything other than curios and objects of affection.

  9. David Roberts Silver badge

    Generational thing. Passed me by.

    By the time this came out I had been computing on mainframes for a long time so had no real idea that small computers were a thing.

    Only really got into it when the kids were old enough to take an interest, and got an Atari STe which also did word processing and spreadsheets. Games for the kids, of course. Dot matrix printer that could do imitation hand writing instead of the usual fonts.

    Fascinating how a decade of enthusiasms can pass you by if you are the wrong age.

  10. Binraider666

    Late to the party

    I started off on the Spectrum 48K, which thankfully had a keyboard better than a calculator. The manual, to this day, is still a great primer on BASIC programming. Not a great primer on basic programming, of course. I can hear the academics turning in their graves over the use of GOTO rather than functions!

    That machine got lemonaded while meleeing over a joystick; so we went backwards to a Sharp MZ80 for a couple of Christmasses, then leapt forwards with a C64. To this day I'm grateful to my Dad for putting us through the iterations as it's ultimately been my ticket to a job ever since! I'll be damned if I could still remember how to use the MZ80, but all the other machines I can still bodge my way through.

    I recently returned to the C64, fully re-capping and heatsinking the whole system and the excellent Epyx Fastloader Reloaded cartridge with an SD card reader. You forget how hard programming is without a proper text editor or variable names longer than two characters. The C64 programmers reference is hilarious. The complete opposite of modern editing practise. I don't know, encouraging the use of super-condensed code, avoiding comments, minimal spacing, condensing multiple functions into single line numbers and using near-unreadable short symbolic codes for the BASIC keywords.... The kids don't know how easy they have it with Python and virtually unlimited resources!

    It even encourages you to jump into assembler for maximum efficiency. Hard to find assembler being actively used now, other than for a handful of specialised operating system functions... And even then most of the op system you are reading this on was probably done in C or C++.

  11. martinusher Silver badge

    I never went the Sinclair route

    My forays into early home computing started with a Superboard (6502/ROM BASIC), an Osborne 1 and a Jupiter Ace. The Jupiter was similar in size and general crappiness to the ZX81 but ran FORTH which meant you could actually do useful work with it. I've always thought that the history of computing took a number of wrong turns, one of the really bad ones being computers running ROM BASIC such as the ZX81 and the BBC; these types of machines taught a generation of people not only how to write code but also not how to program.

  12. ricardian

    My first OU course was PM957 "Computing & computers" in 1977. I lived in Brora, Sutherland and all my coding (OU BASIC) was handwritten and sent off to the OU computer centre where it was keyed in and run, the results (warts & all) was then posted (Royal Mail) back to me. Later I did another OU course in computing which had HEKTOR, a small machine akin to the VIC-20 which fed an analogue TV. Great course, began hand assembly before progressing to a "proper" assembler and finally a version of BASIC).

    Later in 1984 I worked in R&D for a large government department which bought a few Commodore PETs. With the invaluable help of Raeto West's hefty handbook I taught myself 6502 assembler and produced some useful programs; some of which included speed-up tricks which avoided floating point operations such as multiplying by 10 by shifting left 3 times and then adding the original number twice. I remember that all the IEEE488 (GPIB) routines were hard coded into ROM and that there were a couple of spare sockets for "home-brewed" EPROMS.

    Then we got the first IBM PCs and shifted to "C" using the Aztec compiler. Still good fun though

  13. AndrueC Silver badge

    At least the membrane keyboard featured an early version of Intellisense, with commands and functions popping up while the user typed. A proficient user could rapidly fill the diminutive memory with only a few keystrokes.

    Actually, no. Like all versions of BASIC that I'm aware of the keywords were tokenised once stored in memory. What the article author is describing is some slightly clever keyboard handling that knew the rules about keywords and automatically put the keyboard into an appropriate shift state such that keys generated token codes instead of letters.

    With a lot of computers you typed 'PRINT "Hello"' and that was 13 characters. However a parser then stored that in memory as <PRINT token>"Hello" which meant it only occupied 8 bytes (note how the space after PRINT can be discarded by having the <PRINT token> expand to 'PRINT '.

    What the ZX81 was doing (and the Speccy did the same) was to put the keyboard into a shift state whereby the 'p' key generated <PRINT token> (Character 0xF5 on the Speccy). This saved typing and simplified the parser but had no impact on the amount of memory consumed while entering program statements.

    How interpreters optimise code storage is an interesting subject. My favourite 8-bit machine was the Amstrad CPC and its version of BASIC stored memory addresses alongside line numbers and variables to improve performance.

  14. MacroRodent Silver badge


    I never owned one, but borrowed from a friend for a while (enough to experience the data loss from the infamous wobbly RAM pack). One thing not mentioned in the article was that since the screen refresh was almost entirely handled by the Z80 CPU, your program ran much faster if you turned it off. The BASIC had FAST and SLOW commands for this. In the FAST mode, the screen just displayed "snow" until the program execution ended.

  15. cutterman

    Ah, what a blast from the past…

    Assembler, machine language, self-modifying code (to fit in that tiny memory space), peeking and poking. I got an AD/DA converter and ran lab instruments with it! The joys of the tape-recorder (not!)

    One trick I used was to modify the return address on the gosub stack to give me conditional jumps to a different code segment - you could really have fun being able to talk to the bare metal of the processor.

    Object-oriented code - why, all my code was OO, long before I'd even heard of it…

    Happy days :-)


    1. Individual #6/42

      Glad to hear I wasn't the only one playing silly buggers

      with self modifying code and the gosub stack. Have an upvote

  16. Hubert Thrunge Jr.

    Kempston Keyboard & Joystick

    Who had one of those as an upgrade to their Sinclair?

    As a teenage yoof, my friends and I "tested" the prototypes of those as the founder of Kempston Micros was out maths teacher.

    He was a very clever guy, but not much of a teacher sadly, or we were just a completely unruly bunch!

    He left the school and set up Kemspton Micros and the rest is history. One of my classmates went on to write software for him while he was at university.

    Nostalgia ain't what it used to be!

  17. ChaosFreak

    My First Computer Game

    OK, so not a Timex Sinclair 1000 but still nostalgic... I managed to get my parents to splurge on a TRS-80 ("Trash 80") as an "educational device" (not a toy) back in 1981 when I was still in primary school. My big sister (six years my elder) was taking night computer courses at Boston University and so we bought a modem so that she could dial into their PDP-10. I soon figured out where she kept her password and spent hours playing "adventure"... when I finally got a Commodore 64 a few years later, the first games I bought (OK, downloaded from a pirate BBS) were the Infocom games as opposed to the flashy graphics games, which were WAY more engaging. I remember spending almost 48 hours straight solving "Planetfall". But try and tell that to kids these days...

    I did manage to teach myself BASIC from the manual included with the TRS-80, the start of a long and satisfying career. My sister also has spent her whole career coding. I think she made it in just before the home computer industry decided that computers were "toys for boys" and began marketing exclusively to boys. Most of the jobs I worked in the early days had a very healthy (even by today's standards) mix of gender among the programmers, but that was a window that soon closed, unfortunately.

  18. Anonymous Coward
    Anonymous Coward

    I still use mine

    It's in the loft, controlling my central heating. Needs to be started up again whenever there's a power outage but other than that, it's been fine for over thirty years (so far).

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

      Re: I still use mine


      I still use mine

      It's in the loft, controlling my central heating. Needs to be started up again whenever there's a power outage but other than that, it's been fine for over thirty years (so far).


      You sir win the internets. And to think I still feel guilty when I go to my old house and see the underfloor heating controller running on a pentium 90 powered toshiba laptop with a broken screen, running some years out of date version of redhat linux (hedwig I think was the last time it got upgraded, relax its now totally airgapped for some years now, although at one point it was the NAT and fax gateway for the house via a modem at the same time :p ). When I power it up and hear that brick being dragged round on a slate roof from the tiny hard disk and marvel that apache still manages to come up clean and present a working gui, until that bit works parts of my nether anatomy tighten slightly while I worry if I can rebuild it and redeploy all the source to something newer assuming I can find something with the right hardware ports to interface to my homemade controller while wondering if its finally time I swapped it for a atmel based pic system I made a few years back as contingency.

      I bet you have a couple of spare zx81's stashed as DR too...

      1. Anonymous Coward
        Anonymous Coward

        Re: I still use mine

        No redundancy I'm unhappy to report... ebay hunt while the Pest From The West freezes my nuts?

        My old PII266 laptop has been happily running off a CF card for years recording CCTV... quietly. Boots XP in under 20 seconds. When it was my software development machine, battery life trebled running off CF. You could get an IDE to CF converter, clone the drive. 'Board, RAM spares are easy to source on ebay of course.

  19. Stephen Wilkinson

    I started with a ZX-81, then a Commodore Vic-20 and then a Commodore 64 before going out to work doing data entry on a IBM System 360.

    Then off to uni to study Software Engineering and a career (employment more like!) so thanks very much Clive, it's all your fault! :D

    I didn't think the Commodore 64 Programmer's Reference Guide was bad, I've still got mine although I don't refer to it anymore.

    Back to the ZX-81, absolutely loved Mazogs and 3D Monster Maze but 3D Defendr was virtually impossible to play - great times to be growing up.

  20. Android Hater

    Just In Time Stock Control

    Yeah, I wrote a Just In Time Stock Control and ordering system for the ZX81. It needed a minimum of 16KB, 32KB was better. Lots of hacks to save memory: PI/PI for zero, Peeks and Pokes everywhere.

    The data was held on tape and needed loading into the arrays which could take 5 minutes to 10 minutes or longer.

    Amazingly, it worked and reduced our stock holding nearly 70%! I seem to remember even selling it to a number of companies via ads in the computer rags.

  21. War Puppy

    I was given a ZX81 as pay for my 1st ever dev job that was developed on my ZX80 (paid for through much wrinkled skin, car washing my weekends away).

    Basically my dad was a Quantity Surveyor, barely using a calculator (up from slide rule) and I wrote some code to work up costing for a building after inputting some basic data. From an hour down to 10 minutes.

    We went into his work, where slack jawed Neanderthals witnessed the future as I priced up a drawing in 10 minutes, that their best took 40 minutes over.

    I do miss the days of wonder, as 'new tech' appeared weekly or monthly in magazines, I had to travel on a 1 hour bus to buy.

  22. russmichaels

    amazing that this thing actually had a 3mhz processor but was so limited and rubbish. To think the C64, the best home computer of all time, only had a 1mhz processor, yet was a 1000 x better.

    1. This post has been deleted by its author

    2. Andy3

      Yes, but there was a rather large price difference!

  23. Chris Johnson 1

    Capable of so much more

    My first outing with the ZX81 involved developing a new ROM for it to allow it to function as an assembler development station (ZX ASZMIC). Its biggest problem was the absence of dot-addressable graphics but by shorting out two lines on the rampack connector (others used diodes but these were not actually necessary). Once that was done you could have new character sets which included lower case and, by stealing the stack address used by the command interpreter, introduce exciting new commands for it. I had everything from line drawing commands to sprites and even windowing like that new-fangled Lisa computer. Fortune was assured, and then evil Clive introduced the Spectrum with colour and killed the ZX81 market :-(

  24. andyL71

    Say to Thorin "carry me"

    I saw my first computer in 1981 at primary school, when they were brought round for the kids to look at as part of a national programme. I was captivated and spent the next 2 years drooling over computer magazines, code listings etc. Every small town in the UK seemed to have its own computer shop and every time my folks took us on a day trip I would find myself with my nose pressed against a window, speculating on the relative merits of Dragon 32, Vic 20, and Spectrum.

    Spectrum won out, and I loved it. Perhaps not the highest level of quality - 6 passed through my hands in the early months of 1983 (including 2 in one day). It absolutely led to my career in IT, and Speccy No. 6 sits in a cupboard behind me as I write this.

    I won a modem for it in a Blue Peter competition, along with a year's subscription to Prestel, which I used for a space MMO and my dad used for Bank of Scotland Home Banking. This was around the time of the Duke of Edinburgh hacking scandal.

    From the code listings in magazines like Computer and Video Games and a bit of graph paper I figured out how to create and move 8 bit sprites. I sometimes wonder if programming a sprite of a helicopter to buzz over the screen and fire a missile at a sprite of a tank might be the best thing I have ever achieved in IT.

  25. Gordon 8


    I had a new ROM ZX80, and then a ZX81.....

    It was passed on to someone else when I got a Commodore 64....

    However at a Radio Rally in the early 90's I saw one with an original RAM pack for 5 Pounds

    I Still have it and last time I checked it works. I even brought it 8,000 miles to Singapore.

    I don't have a TV that works with it any more.... My Flashy Samsung thing does not seem to work with it.

    Beer for Sir Clive...

    Mine's the coat with the pocket large enough for a Zx81....

  26. Anonymous South African Coward Silver badge

    How long till we do the 48k Speccy's 37th anniversary?

    1. Anonymous Coward
      Anonymous Coward

      The speccy is 36 years old in April this year.

      You can order a future-proofed for another few decades version from

  27. Andy3

    Oh gosh, what memories! I bought one in 1981 and proceeded to teach myself Sinclair Basic. I was enthralled by the feeling of control, the way I could change a line of Basic and make different things happen. Before too long I was writing simple games like reaction timers and even a (rather slow-running) shooting game. We later got a BBC-B and that was a speed-monster compared to the Sinclair and I even managed to write a weather-fax decoder for it, all in BBC Basic. Happy days, and all in just 1k for the Sinclair and 32k for the Beeb! We've still got the BBC (and it still works), but I really wish we'd kept the Sinclair.

  28. Badgerxx

    Wireless ZX81

    My local radio station (Pennine Radio) in Bradford had a computer show where us budding geeks and nerds could post in cassette tapes of our latest lunar lander or bubble sort programmes for broadcast over the airwaves. Fellow geeks could tape the whistles and beeps and share in each other's creativity without ever having the meet in person or speak to each other on the CB radio! Happy days.

  29. Umpty Numpty

    Space Invaders

    May only be 1024 characters, but it took a bit of typing in in Assy

  30. Munkstar


    Got bored very quickly waited for the iPhone.

  31. StorageCamel

    ZX81 vs Atari 2600

    I had a ZX81 and later got the Sinclair 16KB RAM pack...the wobbly one.

    Missile Command was pretty easy to program on the ZX81, even in basic.

    Back then I showed it off to a friend of mine who had the Atari 2600. Apart from the colors and sound it looked like the real thing. That was until I got the Atari600XL of course.

    My main issue was that the off-the-shelf portable cassette player ( I think Panasonic) did only load the games once in a dozen times, despite me endlessly fiddling around with the volume.

  32. Curator

    My first computer and the start of a 30 year career in IT. If anyone wants to have a play on one, we have a working one at the Museum of Computing in Swindon.

  33. unwarranted triumphalism

    Still a better computer that anything by crApple.


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