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author's profile photo Morten Wittrock

ZX81 RAM pack wobble woes

This tweet brought back some memories :-) The ZX81 was my first computer. It had a whopping 1 KB of memory (yeah, 1024 bytes), which you could expand to 16 KB with the RAM pack. The cartridge’s connector was notoriously wobbly, though, and moving it even slightly would crash the computer. At age 10, when my parents got me the computer and RAM pack, I was blissfully unaware of this problem.

I started learning a bit of BASIC from the ZX81 manual, and I managed to write a very, very simple adventure game. In the first location you had a choice of picking up a gold coin or leaving it, and in the next location you could cross a bridge, if you had a gold coin to pay the toll with. Something along those lines. Not very advanced, but hey, I was 10 years old :-)

I had written this game, and I was looking forward to showing it to my sister later in the day. Now, the ZX81 used cassette tapes for storage, but for some reason, that I can’t remember, I couldn’t save it to cassette. No problem, I thought at the time, I’ll just leave the computer on. But when I got back to it later, the screen was blank with only the K cursor bottom left. My program was gone.

It seems obvious to me now, that someone had moved the ZX81 to make some room on the desk, thereby causing a RAM pack wobble reset. But at the time I was baffled and quite upset, since it had taken me a very long time to get the program to work. But at least I learned a valuable lesson about computers at an early age :-)

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  • Dec 19, 2016 at 09:58 AM

    My first computer was not sooo old school (already a PC with Win3.1), but I remember the times when thinking about harddrive and RAM in GB was a thing of science-fiction. ^^

    I was excited when my harddrive finally went beyond the 100 MB capacity (what to do with all that space?!). And when I could buy a new RAM with 128 MB. And later on even a second one! Man, those were expensive.

    • Dec 21, 2016 at 07:26 AM

      128 MB!?

      I was happy when my old 486 was upgraded with 16MB of RAM!

      Ahhh! good old times!

      • Dec 22, 2016 at 06:31 PM

        Yes, I was further down the road with that thought. ^^ Going beyond the 100 MB was "woaaaah".

  • Dec 19, 2016 at 04:17 PM

    Mine was a Commodore Vic20, also with a cassette tape drive, and a 300-baud modem. I used a portable 4" black-and-white TV as the monitor, in my college dorm room

    • Dec 19, 2016 at 08:58 PM

      That was actually my second computer. A massive upgrade from the ZX81, with its proper keyboard, colours and, you know, sound :-)

      • Dec 19, 2016 at 09:14 PM

        Yeah, and 22-column screen. :) Though I used a terminal emulator program on it that expanded it to 40 columns, at the trade-off of being in all caps.

  • Dec 19, 2016 at 08:29 PM

    My first one was good old Soviet BK-0010. Technically it was not mine, my mom and dad have been borrowing those from work occasionally. Don't know who writes those Wikipedia articles but there was no way anyone would have this as a "home computer" in the USSR. First of all, 600 rubles was 3x monthly salary for an average Engineer (which could buy about 600 3-course lunches or 6 pairs of Levis jeans on the black market) and, second, they simply were not easily available in stores.

    • Dec 19, 2016 at 09:24 PM

      I like that keyboard!!

      • Dec 20, 2016 at 06:24 PM

        The picture on Wikipedia is actually the later 0011 model. The very first ones had sort of a thick plastic film instead of the actual separate keys. It looked rather glamorous and futuristic at the time but was terrible pain to use and broke frequently.

  • Dec 19, 2016 at 09:08 PM

    Mine was an "8086" IBM clone. In fact it may have been an "8088" or another of the variants but "8086" was always what my dad called it. I recall that it did not have a "turbo" button like some of my friends newer computers did. I always thought having a turbo button was so cool but I did not understand how it worked at the time. The turbo button actually slowed down newer computers so that software designed for the 8086 could be run on them. I recall the first computer in school was the Apple IIe. I don't remember which version.

    • Dec 19, 2016 at 09:17 PM

      In the early days of the IBM PC, I had a cheapie videogame for it called Scorched Earth, which was your basic missile ballistics game. It had crude animations of shells launched from stationary tanks, and the animation depended heavily on CPU clockspeed. With "turbo" turned on, the game ran too fast, the animation was faster than you could blink! And later, when I got a 386, it was completely useless.

      • Dec 19, 2016 at 11:59 PM

        Now that you wrote it, I remember... I started with a 386!

        • Dec 20, 2016 at 07:04 AM

          Hm, what version then, a "real" 386DX or the "restricted" 386SX?

          I recall the first computer in school was the Apple IIe.

          Me, too:) - And I remember it took several edit efforts until I realized I had to somehow "store" my first code...


          FWIW, this current CC comment editor with its formatting pecularities (How do I undo "CODE" mode?) requires several edit attempts, as well, not everything has improved over the last 32 years....

          • Dec 20, 2016 at 07:55 AM

            I don't know, I was ~15 at the time and that was the first computer whatsoever I ever came in contact with, so nooo clue. :)

    • Dec 21, 2016 at 07:28 AM

      I still play Scorched Earth (Thanks DosBox!).

      It's still one of the best games imho: easy to understand but tricky to master (wind, rebound and so on).

  • Dec 19, 2016 at 09:35 PM

    I can't find a picture of it but in 19xx we started with a Syntrex Word Processor - a dedicated word processor with a great keyboard. You could logon, share files, etc. Then we graduated to a personal computer with 1 floppy drives. Times have changed fast!!

  • Dec 20, 2016 at 09:06 AM


    Memory lane. (or I do member! for south park aficionados )

    My first computer was the Zx spectrum the one with the rubber keys. A lot of gaming consisted of buying game magazines and then typing over the source code listed in them.

    I didn't really code then, just copied. Now the second home computer, as they were called was I think this Msx 1 Favorite game was the Hobbit text adventure game which took a whopping 15 minutes to load into memory. I was in my early teens and started to play around with coding, a bit of music and some graphics.

    There was also this one extremely difficult shooter called Zanac which I never managed to finish back then. Years later I got my revenge by finishing it with an emulater.

    Later I found an emulator which supported save states and with that I managed to finish a couple of games that I couldn't when I was a kid.

  • Dec 20, 2016 at 09:35 AM

    That whole thread makes me feel somewhere between nostalgic about the Old Days and really old – you know, the "they've got this covered" section from the latter one:)

  • Dec 20, 2016 at 11:52 AM

    Thanks for all the nice stories about your first computers! Keep 'em coming :-)

  • Dec 20, 2016 at 12:31 PM

    LOVE these stories!!!!

    A good friend of mine had a Radio Shack "Trash 80" (TRS-80) which was probably the first time I saw a "home computer". We would play some "Zork"-like adventure game on it for hours (I was in charge of mapping haha). I thought it was amazing. I wanted one. My first a couple of months later...a TI-99 (Texas Instruments) that my Dad brought home one day (he worked at a bank). I learned a bit of programming (from magazines of the day where you keyed in Assembly language code and most had typos/bugs so never worked) and played games from "cartridges" (like an Atari). But the world really opened for me when my Dad brought home my second computer, a Commodore C-64 Educator ...with a cassette tape drive (later I got a external floppy disk drive and thought it was so futuristic) ! Somehow, folks at the bank got a deal on them, so he brought one home for me. I learned BASIC and Terrapin LOGO languages. I wrote a database without knowing I was a directory of all my fellow school mates. Around that time, I learned that another neighbor friend also had a C-64...but his was soooo much cooler...and he had this thing called a "modem". He showed me how to get on bulletin boards, find pirated games, and this thing called "hacking"......and my world was forever changed (haha). But that's a story for another day...... PLEASE SHARE YOURS!

    (ps. I still have my TI-99, a C-64 I got later and several of my early programming "hobbyist" magazines......hoarder? Nah, just a fan of "nostalgia". haha)

    • Dec 20, 2016 at 01:48 PM

      The C64 is still my favourite computer ever. So awesome. I've still got one (and a ZX81, by the way). They both still work perfectly. How's that for longevity :-)

    • Dec 20, 2016 at 03:26 PM

      Bulleitin boards for games were awesome! So many horrible games and so little time to download them all while tying up the phone lines. Still have my Atari and all the games. It's actually listed for sale right now. I was able to get rid of most of the Nintendo stuff and make a nice little pile of cash. I made more on some of the games than I would have paid for them originally.

      • Dec 20, 2016 at 03:50 PM

        Oh the games!!!! "Satan's Hollow" was my favorite that we downloaded. I played it in arcades (wow, there's another blast from the past!) and thought it was amazing that I could play it at home. "Zaxxon" was another top favorite too....but sooo hard!(haha) It was sooo funny what amounted to hacking then....most were some kid got ahold of a hex editor and simply changed some on-screen text to something like "cracked by CRACKER JAX KIDZ" or something silly. Yeh...real hack there! haha....but we thought it was cool and amazing and "how they'd do that?!?!" back then. is a time sink if you didn't know about it ....

        80s Top Computer Games Online

        • Dec 23, 2016 at 02:36 PM

          Your "cracked by CRACKER JAX KIDZ" statement reminded me of all the hacks of AOL and AOL Instant Messanger from the 90's. Except they would have written it like this, "cRaCkEr JaX kIdZ".

    • Dec 20, 2016 at 06:39 PM

      My husband and I met on a bulletin board, which is very difficult to explain to other people these days.

  • Dec 20, 2016 at 02:00 PM

    The first PC, which we got at home, was a 286... yay!
    At that time it was very rare that families could afford such luxury - it was about a year's worth of salaries for an engineer, and even if you had the money, you needed really good connections to buy one.
    Of course, I did not have it all for myself - my father used it for work (he made construction modelling calculations with it, which was our main source of income).
    The PC had DOS 5.0, some MSOffice program equivalents in Bulgarian, GW-BASIC. Of course, I got a few games on diskettes from reputable sources (it is good that we also had an anti-virus installed).
    A few days after we got the PC, I waited for my father to go out for work, locked myself into his study and started disassembling. Unfortunately, he came back earlier, than I expected.
    Dad tried to rush into his study and realizes that the door is locked from inside.
    'Vesi, what are you doing there?'
    'Don't worry, dad, I am not with a guy!'
    'WHAT ARE YOU DOING? Open the door! Immediately!'
    I opened the door.I had no escape plan... silly me.
    Poor dad, he almost fainted, when he saw the components scattered around the room. He sat down and said quietly: 'I expect no parts will be left unassembled when you finish'.
    At that time, I did not realize, that I was acting irresponsibly, I went on explaining in a very cheerful manner what each part is used for and how do you assemble and disassemble it... I think, this is how parents get white hairs.
    I managed to assemble back everything, I turned the computer on and everything worked just fine.
    Many years had to pass until I realized, that I was supposed to apologize...

    • Dec 20, 2016 at 02:25 PM

      So good! It reads like a scene from a movie!

    • Dec 21, 2016 at 10:46 AM

      What a cool story, reminds me a lot of me.

      I was not a nice child, I was extremely inquisitive and autodidact reading and writing. Alas for my parents, self-exploration did not stop there.

      I wanted to know how stuff works and in the process dismantled many appliances in our household since I was about 3,5 years old. About 1,5 years later I figured out how to reassemble stuff, much to the relief of my parents you can imagine :)

      • Dec 21, 2016 at 03:48 PM

        Yeah I bet the folks who post "dear gurus, my client has a requirement..." questions on SCN were super nice children and never disassembled anything in their lives...

  • Dec 21, 2016 at 04:16 PM

    The first computer I owned was an Acorn System 1. It looked like this:

    Hex keyboard, single line 8 character, 7 segment LED display, 1 kB RAM, programmed in hex. It cost me about £100 in 1981 (apparently almost £400 in today's pounds). There was no permanent storage. A cassette could be attached, but you had to key in (in hex) the save/load programme manually before you could use it:-)

    I actually *loved* this machine, and learned so much about how computers work from it, much of which knowledge I still make use of today.

    After this I became a student, and then got a job, and saw no point in spending my own money on computers since I had access to much better devices than I could ever afford through the University. The next machine I bought was in 1994, ran Windows 3.1 (later Windows 95) and had 1024x more RAM (a whole 1MB:-). This one ended up on the internet via a 9600baud modem!

    Oh the memories...

    acornsystem1.jpg (23.2 kB)
  • Dec 22, 2016 at 08:28 AM

    The first computer I used was a DGC Nova 210. The first I owned was a Kim1

    followed by a UK101

    with 2K of ram. I found an old Phoenix Disc drive (10Mb fixed/10Mb removable) in an 18" rack at a scrap yard. Refurbished that and wrote myself a disc operating system. The drive sounded like a jet engine starting up and initially drew 30amps which caused a problem with the fuses....(Hmmm.....)

    I'm currently going through a phase of getting emulators for all the machines that I have used. The most interesting so far is an IBM 370/185 running MVS and JES2. I can also boot Music and Vm370.....

    My scrapyard exploits continued, eventually ending up with a PDP 11 and a couple of ADM3A terminals. Luckily enough the scrappie hadn't touched any of the platters for the PDP so I also had RSTS/E


    • Dec 22, 2016 at 01:34 PM

      WHOA! Pretty dang cool!

      • Dec 22, 2016 at 03:19 PM

        I also helped a friend lug an ICL 2903 upstairs to his workshop where when he plugged it in for the first time it promptly blew up..... Said friend was doing something inside the terminal that housed my UK101 (head and right arm fully inside). I swear....Honestly!! To this day he said "turn it on"..... And spending 400 quid on a (I think it was) a 68010 maths co-processor back in the early 80's and watching it curl up in a puff of smoke on a bread board was disheartening to say the least....

        Oh.... and talking of MVS/JES2 etc HORST!!! How about an IDES of R/2 that I can host ????

        • Dec 22, 2016 at 04:01 PM

          hahaha I used to tinker with building my own computers and such. One day, a friend of mine was working on his. I had warned him NOT to go in there without knowing what he was doing...and namely making sure we was grounded and static shock protected. He called me later and said, "I don't know what I did but nothing is working now...I turned it on and a little puff of smoke came out." I laughed and said "Oh wow! You did it! found and activated the 'magic smoke' release controller!" =) All electronics come packaged with a magic smoke chip. =)

  • Dec 22, 2016 at 11:30 AM

    I remember playing 3D monster maze on the ZX81. Nothing worse than trying for about 3 hours to try to load the game, only to knock the damn thing when its nearliy finished loading and having to start again.

  • Dec 22, 2016 at 12:14 PM

    The first computer I had access to was a ZX80 my dad brought home from his school. I wrote a lunar lander type game for it.

    The first computer I owned was a ZX81 with a 16K RAM pack. One time, as my mother was hoovering, she managed to snag the power cables and the whole thing fell to the ground, bending the wires in the connector of the RAM pack - to such an extent that it never crashed again.

  • Dec 22, 2016 at 02:06 PM

    Dang.. I don't know the first computer I used. It was a school mainframe for teaching BASIC and the programs were stored on either tape punch or card punch. I used the terminal for the tape becasue I just knew if I used the cards, I'd either drop them or damge one somewhere in the middle.

    First home one was a Commodore 64 and then a IBM XT, (actually provided by work).

    Wow.. how fast things changed.

    Now I know how my folks felt watching cars change in a span of 40 yrs from the Model T's in the 20's/30's to the muscle cars of the 60's/70's. Probably the only other type of technology to make such technical leaps in such a short period of time.

    Of course we have also witnessed the change for telecommunications. From Telegraph, to party lines, to landlines, to mobile phones in briefcases, to pocket cell phones.

  • Dec 23, 2016 at 10:12 AM

    Our first computer was the ZX81, which we bought for $50 in kit. My father and I assembled it (mostly him) and we even expanded it from 1K to 2K! My first adventures in basic. From there we went on to the Sinclair QL with those infernal microdrives (little infinite loop microcassettes). For work, my father bought himself the Cambridge Z88 (another Sinclair idea). This was a great little portable machine. Thanks to its rubber keyboard, my father could quietly type away in meetings and on trains. He would always get curious looks from neighbours wondering what this quiet machine was. Then the switch to PCs.

    Olivetti in DOS (and wordstar!). Amstrad with GEM graphic interface. Then windows. Now Mac. Looking into Linux now...

    ...but my heart is still beating for those Sinclair machines...

    • Dec 23, 2016 at 10:19 AM

      The old computers did have more, for lack of a better word, personality, than the much more powerful, but also more generic, machines we've got today. I miss them :-)

      • Dec 23, 2016 at 02:44 PM

        It's kind of like old cars/trucks. They had more personality too. Now you just get in and drive. Doesn't matter what car they are nearly all the same. I can remember my old truck, you had to know it just to get it started, let alone drive it. Is it hot outside? Push the accelerator 1/4 down while turning the key, lift off after first turnover. Is it 32 or below? Push the accelerator to the floor 3 times. Release. Turn the key. Push pedal down slightly while turning the key if it won't start on first few turnovers (usually when humid). Is it below zero? Try all of the above while praying.

    • Jan 04, 2017 at 08:09 AM

      WordStar brings back memories....... And CP/M.

  • Jul 29, 2018 at 02:52 PM

    This seems on-topic :-) By the way, I was able to get decent picture quality on a (reasonably) modern TV. When I hooked up a Sinclair ZX81 to the same TV, the screen was way more blurry.

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