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5 March 1981: The ZX81 home computer launches with 1kb memory (wikipedia.org)
125 points by open-source-ux on March 5, 2017 | hide | past | favorite | 85 comments

My first computer. Ordered the day it was released after saving up 50% of the £70 and my father added the other 50%.

Finished secondary school whilst waiting for it to be delivered, it arrived the following week - the first week of June 1981.

I spent the intervening months teaching myself BASIC programming from the total of 3 books on programming in the local library.

I remember the day it arrived well; I was busy cleaning house and didn't realise the postman had left the parcel in the kitchen until I stopped for a break a couple of hours later.

Had it unboxed and connected in a flash and I was still to be found lying on the lounge carpet in front of the television programming it (in BASIC) at midnight.

Started my agricultural apprenticeship the following week and continued programming late into the nights, quickly moving to write pure Z80 assembly language code.

Dropped the apprenticeship a year later, went self-employed, and been hacking ever since.

I still miss those days of actually counting the clock cycles of different instruction combinations to find the most efficient code via the look-up tables in the back of Rodnay Zak's "Programming the Z80".

Oh, and we had to manually enter the hex codes of the instructions to write those programs - before there was a decent assembler available.

I recall adding a full-size mechanical keyboard, a 16KB RAM-pack, and a weird multi-port expansion dock that had add-on modules (like a light pen) built into cassette tape cases and connected via a single-in-line pin connection.

I still have that original ZX81 along with a UHF<->VGA signal adapter. Time to fetch it out of its shoe box and fire up the nostalgia.

The Zaks book! I remember thinking it was such a weighty tome when I was a child, then being surprised to discover as an adult that it was just a regular sized book.

The ZX81 was best described as a terrifying bundle of hacks flying in close enough formation that from a distance it looks like a computer... a real masterpiece of hardware design, in a disturbingly twisted sort of way.

Also, the official manuals had some of the best cover art ever seen on a computer book, by science fiction artist John Harris:




My first computer.

To give an idea of the state of computing back then, the manual states (I checked now)

> to get '+' you must hold down the key SHIFT and while you are still doing that, press the key K.

Not something you find in user manuals now.

My English was so bad back them that I couldn't understand the full meaning of the sentence and I couldn't go through the example. I asked my classmates at school the day after. My mother was a touch typist but she didn't realize that the tiny keyboard of the ZX81 could work like the one of a typewriter. Computers were beyond geeky.

Not something you find in user manuals now.

Indeed, perhaps mostly because user manuals themselves are not something you often find now.

The reason I learned English was to read manuals and program my Soviet clone of ZX80.

Me too but for a C64 in Iran.

There should still be Berlin wall. Love to see genuinely good things spreading.

I wrote it wrong, I wanted to say that I vaguely remembered that the whenabouts of 1981 were wall's times, and referred to the computer design spreading.

My dad ordered it when it hit the States for, I think, $300. He was an English teacher and suppressed gadget freak (we weren't rich). He returned it because he couldn't see a practical use for it. I wasn't interested in computers. He died two years later. I went on to become a successful programmer and very successful businessdude. I deeply regret not being able to buy him every single PC, Mac, iPhone, and iPad that came out those many years later.

My first computer was ZX Spectrum (a successor of ZX81). By coincidence, a few days ago, I've finished reading the book "It's behind you" about development of R-Type, a top-notch arcade which pushed ZX Spectrum to its limits.

Here is a link to official free copy of this book:


About game:


Gameplay of R-Type on ZX Spectrum:


I'm still playing ZX Spectrum games once in a while in the urge of nostalgia.

> I'm still playing ZX Spectrum games once in a while in the urge of nostalgia.

Me too. Was playing Horace Goes Skiing earlier this week, but my all time favourite game is "Chaos: The Battle of Wizards":


(This is available to play in your browser, online. Fun!)

Back in the day I used to hack games for infinite lives, and received a bunch of swag from Your Sinclair, and Sinclair User for posting them.

I credit the 48k Spectrum with getting me into programming, first BASIC then Z80 machine code. (Largely because the "bundle" we received had a dead tape-deck, so for the first couple of weeks the only thing we could do with it was read the manual(s) and type in simple programs..)

I swear i ran into a clone of that game for either DOS or early Windows at some point. Would love to find it again.

Don't know R-type, but Rockman did speech [1] on a machine whose buzzer only admited 2 states (some sort of PWM?), and Uridium [2] did multicolored characters by changing colors in interrupts handled in controlled TV scan-lines.

[1] https://www.youtube.com/watch?v=UyFrOHDDXrU [2] https://www.youtube.com/watch?v=6S8rGc4Osu4

That latter trick was used on many an early micro that was designed for TV use. Back then games had a very intimate relationship with the CPU and the electron beam of the TV.

For example using the cycles while the beam was moving from the bottom right to the top left to start a new image to do non-graphical work.

That book is great and a nice quick read, and though it's focused on one developer's work on making one game, gives lots of insight about the environment that he worked in and how things were done. You get a lot of the sense of the milieu of the U.K. 8-bit computer industry.

I really wanted a ZX-81, and my dad ordered one not long after they came out. But typical for Sinclair, the delivery lead time was on the order of months! Not even weeks or days, and my dad gave up and brought home an assembled Acorn ATOM that one of the techs at the university has soldered up from a kit.

Great little machine, and introduced me to programming in ATOM Basic and 6502 assembly, leading to a career in computing that's still going 30+ years later.

Oddly enough, I just ordered parts from Mouser to build David Johnson Davies' Tiny Lisp Computer 2, ... DJD being the author of ATOMIC Theory and Practice and Practical Programs for the BBC Computer and ACORN ATOM.

I had a similar story with the Spectrum; they had industrial action and wound up not shipping. My dad cancelled and bought a Commodore 64. I think I dodged a bullet there (although I'm sure the Spectrum would have been interesting).

Haha, I remember that. My maths teacher DM had a mate in the factory who eventually got me a speccy out the factory door, but it was a longgg wait. Spectrum was a fun machine. Basic was ok for very simple games. I never did learn z80 assembler.

This was my first computer, and I remember it fondly.

Sadly, my parents dumped it (and my two ZX Spectrums), but I still have one of the manuals squirreled away.

Edit: JS emulator, for that extra touch of nostalgia


The first computer I used at home was either this or the Timex Sinclair 1000. Membrane keyboards are the worst.

I did learn a lot about modern day programming, though. Everything I wrote was really just copy/"pasted" from a book or magazine.

I found a replacement in ebay a few years back.

But no I don't have the TV to plug it in!

I might never have gotten into programming or IT without the ZX81, dodgy RAM pack, crappy keyboard and complete lack of audio included!

I wonder if anyone has managed to connect a ZX81 to a modern display? Apparently the design cuts corners, omitting the "back porch" part of the signal, so modern TVs cannot determine the correct black level, and display everything black.

(More here: https://www.vintage-radio.net/forum/showthread.php?t=73664)

Modern TVs are pretty poor at displaying analogue video. All sorts of retro computers and consoles have quirky video output. Most retro enthusiasts use an old CRT TV, typically a late-model Sony Trinitron. They're as cheap as chips these days. If you're really keen, you can't do better than a Sony BVM broadcast monitor.

Tell me about it :-/ I've been trying on and off to hook up my PS2 to a 55" flatscreen TV, and it's been a trial. The TV has component video inputs, and I have the appropriate PS2 component cable, but certain US games cannot be played because the TV cannot handle "too low" (480i) resolution.

How hard could it be to design a circuit that would reshape the video signal into something reasonable? Or to feed the video signal into an analog input and reprocess it in software?

The canonical solution to this problem is the Framemeister XRGB-mini, which can convert pretty much anything into a 1080p HDMI signal.


I do wonder if whatever is sitting at the heart of that thing has more computing power than the ZX81.

Lovely kit but also £450 in the UK :-(

Yeah, I see no reason why such a thing should cost as much as a smart phone. You should be able to do it with a Raspberry Pi Zero plus the right software.

Apparently there are alternatives, including an open source one. This video talks about them: https://www.youtube.com/watch?v=lHoOKLWIMKU

Also my first computer. Definitely a gateway drug. I was lucky enough to have a 16k RAM pack (held on with blutac). Later we had a series ZX Spectrums, the Acorn Archimedes A440, then an Acorn RISC PC. After that, boring x86 only :/

RISC OS today runs natively on the Raspberry Pi, if you want to revisit your history.


I do wonder how well it works with one of those Ceed Pi-Top products.

You can buy a Pi-Top with a custom version of RISC OS preloaded.


My first home computer. My other non-home computer being an IBM mainframe. ;) Still sitting in my parents attic somewhere. I gotta get it up and running again.

I really wanted an Atari video game console but my parents thought the ZX81 would be more educational. And I guess they were right.

Endless hours on the floor in front of the TV writing programs in Basic with that spiral bound user's manual for reference. I got the 16KB expansion pack since the 1KB grew old pretty fast.

I remember the user's manual had the pins for the expansion port and a list of all the Z80A assembly instructions. I spent hours looking at those having absolutely no clue what that was. No Internet to look things up back...

I also upgraded to the Spectrum. An then surprisingly enough to an Atari 512ST after the next Sinclair, the "QL", turned up to be a bit of a fail. Really should have gotten an Amiga in retrospects ;)

Anyone remember the tricks to save a few bytes when you didn't have the 16KB extension pack?

A number (in source code) used a lot of memory, 6 bytes or so, while a command used only 2 bytes, so you would replace numbers by VAL("1") or ORD("A") or something along those lines, saving a full 3 bytes... :-)

My first computer as well. As there was no hard drive included, I had to save on audio tape the programs I was inventing or typing from UK 'Your Computer' weekly magazine. Also, graphical definition was 64 by 44 if I remember well, meaning that imagination was welcome when playing 'games'!

IIRC, graphics used 2x2 block characters. With 24 lines of 32 characters, that would give you 64x48.

However, video memory ate into your 1k RAM. At 24 lines of 32 characters, a conventional video memory would need 75% of that 1k bytes, so they did things differently; video memory was laid out as you would do in a text editor, with each line ending in a line separator character.

That way, an empty screen took just 24 bytes, a full one (32x24) + 24 = 792 bytes, leaving 232 bytes for a program.

=> few programs for the 1k version could use the full screen.

You are correct, but the screen's last two lines of text required some tricks to take advantage of (search for “reserved” in http://www.tebbo.com/archive/pw810601.htm ), so “64x44” is also a correct description from the programmer's point of view.

The particular trick that enabled the program to use the last two lines was easy to come by (I was in the countryside, hundreds of kilometers from the nearest user group, and I only had a few books as source of information). The existence of such tricks, including the pure software “hi-res” more that I read about at the time but didn't get to see until the Internet made it possible 12 years later, is one of my fond memories of that era.

Also the reason why 1K Chess occupied the left hand side of the screen. That way it needed much less video RAM. Screenshot: http://www.retrogamer.net/wp-content/uploads/2014/02/1k-zx-c...

I remember implementing the Mandelbrot set ("Apfelmännchen"), and it would plot one of those "pixels" every few seconds, so the whole thing only took a few hours :-)

yes but there was that hack that made "hi-res" graphics possible - bubbleman ?

For people interested, there's a small community of Spectrum fans on reddit at /r/zxspectrum and one just for the zx81 /r/zx81

Still have mine but dead, for now; infamous for ribbon keyboard decay, and the Ferranti chip may have died, also an infamous component. But both the earlier kit and the assembled computer made us start thinking about what to do, what can be done.

Chiming in to say, this model was my dad's first home computer in the 80s in Scotland. As such me and my brother did not fiddle with it much; however later on we upgraded to the Spectrum ZX 16K with 48K removable daughterboard, a much more amenable model to children. I learned BASIC on that machine and played all kinds of amazing graphic and text games - I wrote about my experiences with this machine on my blog http://nchristiny.com/history/#fnref:fn-2

Correction: 32K removable daughterboard for a whopping 48K RAM

My first computer. I had already taken a programming course at school. I was working on a project that required some repetitive calculations (designing a loudspeaker using textbook formulas). The ZX81 went on sale at K-Mart for 40 bucks, and I rode my bike out there and got one.

I couldn't get the cassette storage to work, so for several days, I begged my family to not unplug it. I remember one amusing thing about its architecture, which was that it used the CPU for video generation, and did all of its execution of BASIC programs during the vertical blanking interval.

Yes, and it had the "FAST" mode, where the CPU would not do video, screen would go black, and it would race through your program 4x faster :-)

And a generation of programmers whose parents couldn't afford an Apple II continued. I am so grateful for Sinclair, Atari, Commodore, and TI for making computers for the rest of us.

The idea that an Apple II could have been "the computer you used when you were growing up" was a rather late and surprising discovery to me. Nobody I knew could afford an Apple II, and to this day I don't think I've ever seen one running except under emulation. (Of course the Apple came out a good few years before the Sinclairs as well, but I gather it was still sold throughout the 80s.)

My own first computer was a Spectrum, which I loved, but I didn't have access to a colour TV at the time. I got to know all the fancy colour games in black and white.

Schools bought them because that was what schools bought in the late 70's and it did carry over even into the IBM era (1981+). To Apple's credit, they did get how to do educational sales.

I didn't know anyone who owned one personally, but that was probably an income-based observation.

Here in the UK, I think schools in the 70s often had the Research Machines 380Z (https://www.theregister.co.uk/2013/11/13/archaeologic_the_re...) which was a marvellously chunky Z80-powered machine running CP/M.

I used those at school and liked them a lot but, I guess like the Apple II, nobody would have bought one for their home because they were expensive and sold mostly through education channels.

In the 80s they generally switched to BBC Micros, which were affordable enough that some better-off families had their own.

So I can see it being a regional thing that I never used an Apple II -- they didn't appear in schools in the UK -- but I wonder about other countries besides the US. Was the Apple all that widespread anywhere else?

I think Canada, and something about Japan since their was a special model: Apple II J-Plus.

The Apple II was really mostly a US thing. It was more of the higher end of the home computer market. Having a Spectrum makes me think you are from the UK. The BBC micro was basically the Apple ][ equivalent there. I'm from the US and actually had a Franklin Ace 1000 (a cheap Apple II clone that was sued out of existence by Apple) growing up

Yep, I'm from the UK. And it may have had to do with exchange rates, but I think even the BBC Micro (£400 then, £1300 in today's money) was only about half the price of the Apple II. Though I can't seem to find a good source for the UK selling price of Apples back then.

(I'm fairly sure the Franklin Ace was available over here as well; at least it appeared in listings at the back of computer mags I used to get. I never saw one and, at the time, never registered that it was an Apple clone.)

Some variant of the Apple II sold into the early 90s.


Don't forget the BBC Micro - hugely popular in schools and at home, at least in Australia and the UK. The first computer I used was a Beeb :)


Acorn Electron for home use, the Model B was a bit pricey.

Which then begat ARM...

My first one too!

So many things came together back then. On TV I saw a documentary about kids in Japan writing their own games. In our city's airport there was a advertising installation for the IBM PC (forgot which model exactly) in form of a lunar lander game. And my best friend in school had just signed up for a BASIC course taught by students of the local university.

I remember I sat there next to the phone going back and forth, unsure about whether I should do the BASIC course and get one of those strange computers myself, or not. Almost didn't do it.

When I did finally decide it basically set me on the path for my entire career continuing to today.

Of course the first thing I did was figuring out how to do the lunar lander (today I know what I did was the Euler Method).

Edit: I also remember I had a hand-written Z80 op code table of 256 op codes. Using that I would write machine code.

My first ever computer, before the Spectrum and Commodore, when my parents decided to let me touch it. Any combination of pure cyan, red and yellow colors still reminds me of the ZX Spectrum's tape loading screen and its dial-up modem-like sounds.

Also my first computer (though I also had the 8K? expansion). It was already pretty old when I was given mine but it definitely started something. From there to C64, Amiga and then onto PC/Mac where it all started to get a bit boring.

Most likely the 16K "rampack". It was pretty much essential to get anything done with the machine[1]. The rampack infamously suffered from "rampack wobble" where a slight movement of the machine would disconnect lines between the motherboard and the rampack causing a crash. Eventually I got a larger case/keyboard and mounted the rampack internally.

[1] Though there was 1K chess, a mostly complete chess game in 672 bytes https://en.wikipedia.org/wiki/1K_ZX_Chess

That was it! And I remember the wobble well. Had it set up on the kitchen table and the slightest knock would screw everything up. Good times.

The rampack infamously suffered from "rampack wobble" where a slight movement of the machine would disconnect lines between the motherboard and the rampack causing a crash.

Oh, that wobble! Definitely on my short list of the most annoying hardware problems in computing history. You’d spend ages typing in the code for a game from your book, and then just as you were ready to go…

Did teach you to save frequently though, on cassette tape, which only took a few minutes! :-)

Cassette tape? We didn’t have such luxuries until we got an Acorn Electron a few years later! So jealous. :-)

1KiB of RAM (1024 bytes) is 8 times the RAM of the Atari VCS/2600 (1977).

Yeah but it's only 1/64 of the Intertec Superbrain, available for only $11.000 at the time.

Don't forget the 2K ROM. I have the 64K model here.

Or of course the 64 KB of the C64 later... (though that was cheaper :-)

A great progress point! Budget phones now have 1GB RAM, a million times more.

The GPUs of budget phones have 10's of GFLOPS... to make a comparison with the ZX81, what's the fastest Z80 routine you could write to multiply 32-bit floating point numbers? Or perhaps, how fast is the routine in the ZX81 ROM BASIC (by Steve Vickers)?

Thw ZX81 had a 4MHz Z80, but in "slow" mode, about 3/4 of that was occupied in rendering the screen, making it effectively 1MHz. In "fast" mode, the screen went black...

This was the computer on which I first learned to program. After that it was the Spectrum. Then the MSX series.

Does anyone remember the MSX series of computers from various vendors?

My father still has his ZX-81. It was his first computer. I tried getting it hooked up to a modern TV a few years back but had no luck. I didn't have an oscilloscope handy, and there are no LEDs or status lights of any kind on the thing, so I didn't get round to figuring out what was wrong.

It's a pretty cool piece of history though. How many people can say they still have their first computer?

My first computer. 1k of ram and the membrane keyboard, but it worked so well. The inspiration for the raspberry PI.

Seems to have been heavily cloned as well. I think my dad owned one such clone called a Lambda 8300 or some such.

JFYI it has been recently revived (actually more ZX80 like, since it uses only discrete components), article on HN:


I remember it heating up significantly in "fast mode". Amazing times.

and you could use alternate fast and slow modes to make sounds through the TV!!

I was late to the home computer party. I sometimes wonder what would have been if I had started with a Z80 instead of a MOS6510.

my first computer too. I was 10 and spend all of xmas at my grandparents typing in hex. such a cool looking machine even today

Good point, the design has held up surprisingly well!

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