Sinclair ZX81: 30 years old
Tomorrow, 5 March 2011, marks the 30th anniversary of the arrival of the machine that did more to awaken ordinary Britons to the possibilities offered by home computing: the Sinclair ZX81. While its successor, the Sinclair Spectrum, got the nation playing computer games, the ZX81 was the tipping point that turned the home …
This topic is closed for new posts.
You fibber!!!!
The ZX81 didn't have sound.
Shame on you sir!
Perhaps you're thinking of the Speccy?
@ForthIsNotDead re. sound.
Although out of the box, the ZX81 did not have sound, there were a number of third party add-ons that gave you sound.
I had a Quicksilver board that had an AY8910 on it, feeding a secondary modulator to add sound to the TV signal.
Quicksilver also had a number of other accessories including a high resolution graphics board and a programmable character board. You needed an interface board that sat between the ZX81 and the RAM pack, which provided two interface slots for the add-ons. Ugly as sin, and made the RAM pack wobble problem different, but as I added an external keyboard to mine, complete with power switch and reset button, I did not have to touch my ZX81 at all.
As I've said before on these forums, my ZX81 actually had 18K of memory, the 16K RAM Pack, the 1K of internal static memory re-mapped to a different address when the RAM Pack was plugged in, and another 1K of static RAM on the ULA side of the data bus isolating resistors to hold programmable characters that were accessible by changing the contents of the Z80's I register, which was used to hold the base address of the character generation table, normally in the ROM. Happy days!
Actually...
It might not have had sound hardware, but by switching between FAST and SLOW mode you could get the TV it was attached to to play tunes ... sorta .... ish.
Managed to get mine to do a passable attempt at a bit of Bach back in the day.
Actualy it had a 3.5 audio in and out
You could control the value of the output cassette port directly with a poke or machine code. Idealy machine code for ability to change the pitch up and down - could get a good octave and a half out of it. It was capable albiet very limited due to the way it would save your works of wonder to tape or inted load them back up. I also managed to get the same resolution highres(sic) graphics that the spectrum did by rewritting the display control code, ok it was realy slow and not colour but hey I did it. Best part was you could then point to your own block of memory and have UDG's instead of an alphabet and it would actualy run slightly faster than normal as it was running from RAM and not ROM. But you needed to have the wobbly attached to pull that trick.
Nice first machine, went for the Oric after that instead of the Spectrum as it had that technical appeal and a 6502 after that I went Atari ST though I do think I missed out on the whole Amiga area, but we all make mistakes. I know COBOL I'm allowed, OK.
Yes it did (kind of)
You had to put it in "fast mode" and the blanking of the screen was able to be kind of tuned to play musical notes.
Ah! The smell of the Thermal printer
...as we printer out naughty ascii art... he got on a C15 Cassette from an older boy at school...
we burnt out 2 of those printers in a year....^_^
@Bill Cumming
Actually, they were not thermal at all. The paper was covered with aluminium, which conducted electricity, and was 'written' by a wire that passed a current through the paper as it wizzed round on a rubber belt. Where the 'spark' hit the paper, the aluminium vaporized, letting the black paper below show through. Crude, noisy, and completely incompatible with listening to the radio. That is why the 'paper' was silver with black print, and also why you got a new high power supply for the ZX81 if you bought the printer.
I believe that they were not allowed to sell the printer in the US, because (surprise, surprise) it contravened the US electrical interference regulations.
This was an example of innovative thinking that made Britain good at creating ideas, but pretty crap at exploiting them!
Well thats a nostalgia trip
and my MK14 still works - though I've transferred a lot of dust from its 'keyboard' to this one.
The zx81 and rampack are still bluetacked to a piece of board to avoid the cost of a cable but I dont think I've got one of those telly things I can plug it into.
Ahh..... the memories!
My ZX81 is gathering dust in a box in my parents' attic I think. I think my RAM pack gave up the ghost but will have to dig it out and see if it still works. Ours came from a family friend who had departed these shores (for Paraguay as memory serves), I wasn't really into computers so I barely prodded it at the time. Missed opportunity!
I had a look on eBay to see if they're exchanging hands for any kind of money. A basic unit without any of the gubbings seems to fetch around £30 going up to c.£100 depending on additional kit and publications. Wonder whether to punt it now or wait until the Chinese get a taste for computer nostalgia.
Paris, because she has a RAM pack slot too (sorry!)
Raise a glass
Ill raise a glass to a old friend tomorrow, we'll fire up my zx81 and 16k rampack and play mazogs on the big projector for a laugh. Ive already introduced my 6yo to basic on it in the past, although we mostly use a emulator running on a xbox out of respect for fragile aging hardware.
j shifted p shifted p day it is ;)
What was really the spirit of the age was opening the thing up to add stuff. I remember a book called the explorers guide to the zx81 touting adding ram over the udg roms so you could have definable ascii, currah keyboards (although we rolled our own from a ancient industrial keyboard that we had to make the matrix to suit ourselves, being poor) and lots of other general vandal soldering activities. In fact my current zx81 was picked up a few years ago pristine because my original had long since died spewing kynar hookup from multiple places in the quest for comprehension and tinkery. Its spirit of mad hardware hackery lived on, they can't teach that with a degree ;)
MK14
Still have mine. 256 bytes of memory
Programmed it in raw machine code. Nothing like it for building character or driving you insane
So grateful for an 6502 assembler on my next machine ( UK101 )
If so many ZX81s are still around
why not make a cluster of them. It should only take about a million Z80 cores to compete with a netbook
But...
If you run a decent (non-windows) OS then you need just one.
Fact failure
Sorry, but the ZX81 did not contain dedicated video circuitry to prevent the bounce. Instead, it had two modes, "fast" and "slow". In fast mode, it was just like the ZX80, and bounced just as much. In slow mode, it gave priority to maintaining the display, so everything you tried to do went even more like molasses than normal for the day.
For maximum fun, tap out a long line of gibberish BASIC in slow mode, then try to backspace across it. Be aware that you will need something to keep the spiders from building webs on you while you wait for each character to be erased. For even more fun, set this up on one you find in a shop. (This was a common affliction of Timex-Sinclair 1000s (the American name for the same thing) found in US stores.)
ZX81 video circuitry
Steve the Cynic
Fact failure #
Posted Friday 4th March 2011 13:44 GMT
Sorry, but the ZX81 did not contain dedicated video circuitry to prevent the bounce. Instead, it had two modes, "fast" and "slow ..
iirc, video was handled by a ULA and the Z80 cpu, as in the ULA forced the data bus low and fed NO OP opcodes to the CPU, the CPU then reading the character bitmaps from ROM back to the ULA.
9. ZX81 character display timing
http://home.germany.net/nils.eilers/zx81/wilfvid.htm#ch5
Although...
... in 'fast' mode it had considerably more raw processing power than the BBC Computer.
I remember hand compiling assembly language and sticking the byte values into DATA statements in BASIC. These then had to be POKEd into a REM statement at the beginning of a BASIC program. Typing RAND USR <number I can't remember> then ran the machine code for you. Later there was the ZXAS assembler which made the whole process easier. Amazing what could be done in 1k let alone 16k. Which looking back gives you a whole different perspective on the slowness of a 256MB PC!
Anybody else remember 3D Monster Maze? Given the limited (64x48 black/grey/white) graphics it played surprisingly well. Basically just being chased round a maze by a dinosaur but, wow, in your own living room, controlling something on TV?
@AC re Although....
Although I am in danger of resurrecting a long dead argument, I dispute that the ZX81 had more compute power than the BBC micro.
Although the BEEB's CPU only ran at 2MHz, whereas the ZX81 ran at 3.75MHz, the BEEB's CPU was a 6502 that executed most machine instructions in a single clock tick, whereas the Z80 in the ZX81 averaged four clock ticks per instruction, and some of them required up to 13.
This was the subject of endless controversy between Sinclair/Amstrad owners and BEEB/Apple/VIC20/C64 owners at the time.
In general, the Z80 instruction set was more advanced that the 6502, containing more instructions, more addressing modes, and even some proto 16 bit arithmetic instructions (by treating pairs of 8 bit registers as a 16 bit register). The 6502 contained enough instructions to do what was required though, and was considerably easier to program (the bible of both processors, written by Rodney Zak, "Programming the Z80" was at least twice as fat as his "Programming the 6502", and had smaller print to boot). This made the debate a forerunner of the CICS vs. RISC argument, which hinged around similar concepts.
Remember, though, that BBC BASIC was blindingly fast for the time, and it remained the fastest BASIC available well into the advent of 16 bit micros, as documented by PCW's BASIC benchmark that they ran on all the systems that they reviewed.
And the BBC micro had a built in assembler, and a means of passing arguments between BASIC and your machine code, and also documented all of the OS I/O, sound and graphics calls that you could make from your machine code. And of course, the display in the BBC was totally hardware driven, freeing the CPU up to run your programs.
I used to write both Z80 code on a ZX81 and Spectrum, and 6502 on a BBC, and believe me, 6502 was easier, and for basic data manipulation, faster.
Happy memories
The BBC Micro IMO set the gold standard for home computers until the IBM PC came along. With its phenomenal graphics, superb firmware, real keyboard and better looks it trumped the ZX81 and all else.
The ZX80 and ZX81 do deserve praise for being an important step on the road, the ZX81 was a marvel for its time, in minimising the electronics into just a few chips, and was significantly cheaper than the BBC so it can never be a fair comparison between the two. Unfortunately it suffered from 'could have been far better' (*) which plagued Sinclair in near everything he did but he was a giant upon whose shoulders everyone has stood.
On what's inside; I was a Motorola 6800 man myself; and would place that higher than the 6502 but lower than Z80 in terms of architectural niceness. It's a shame the 6800 never got into the mainstream (I used the SWTPC which wasn't cheap and not a games machine), the Dragon with its 6809 should have become the king but failed to take off.
(*) I've still got my Sinclair Scientific calculator. Yes, the one which uses Reverse Polish Notation., has no "=" key. Unsurprisingly everyone who 'stole it' when at school brought it back :-)
@Peter Gathercole
Surely the 6502 takes two cycles to do the most basic operations, in practical terms? It's one cycle to read in the op code, and then a second to perform the thing. I think part of the reason the 6502 gets a bum rap in general is that it accesses RAM every single cycle, whether it needs to or not (or, if you prefer, doesn't properly indicate its intent), whereas the z80 accesses RAM only as required — and that tends to be more infrequent due to the more complicated instruction set.
So as soon as you put a 6502 into a system where RAM is clocked at a similar speed to the CPU but shared with video circuitry, it gets seriously hobbled. Comparing the Electron to the slightly later Amstrad CPC is instructive: the former hands at least 50% of its RAM cycles to the video circuits, causing the CPU to run at half rated speed; the latter hands 75% of its RAM cycles to the video circuits but the CPU continues to run at (per empirical observations, usually passed around as a rule of thumb) around 82% of its rated speed.
Obviously the BBC Micro gets around that by coupling a 2Mhz CPU to 4Mhz RAM, interleaving video and processor accesses, so it's not a relevant concern. I just think it's something that likely affected the tone of the debate.
The real proof is in the pudding. Elite is clearly faster on the BBC than the ZX Spectrum, but that's partly because the Spectrum does a software frame copy, lacking page flipping in the 48k machine. I, Of the Mask, Starstrike 2 and Carrier Command (asll solid 3d polygon pushers with good real time frame rates) on the Spectrum side are probably more impressive than Revs on the BBC, but the market was so much larger and most of those Spectrum titles are sufficiently later that they're probably as much a result of the greater amount of interested talent and various lessons already learnt.
Ashamed to admit it...
I sooooo wanted a Spectrum, but in their wisdom my folks bought me a Mattel Aquarius instead :-( To this day I'm still not quite sure how from my christmas list, they managed to arrive at the word "Aquarius" from "Spectrum Spectrum Spectrum Spectrum Spectrum".
30 odd years later I've still never met another person who had one.
Anyone?
Never had one...
...but do remember playing on one. Quite a decent version of space-invaders I seem to remember.
Aquarius
Yeah, I had one of those. Strange machine. Strange BASIC, with bizarre restrictions on where you could PEEK and POKE.
sniff
was wanting a +2 for ages what did i get an Atari 65XE never knew anyone with those either:(
re: 65xe
I had one!!! (years later, 2nd hand from a car boot even then...)
trying to create my own awesome graphics - as 8 year old it consisted of scanlining my own rectangles and triangles, making up a rubbish version of the Jurassic park logo
don't get me started about the film trailer i tried to do...
RE: Ashamed to admit it...
Never be ashamed! 16 colours, sound, rubber keyboard... I loved mine!
Although I remember playing the Grand Prix' game that came with it... hmmm.
I used to type all the programs from the flipchart book that came with it... concentric circles!
My dream of recreating Mr Do! on it failed however...
LOAD ""
I can recall playing somthing Horace-like on a ZX81, and also messign about with the graphics keys to make something TARDIS-like. Though my own first computer was a Spectrum+ a few years later.
Quality problems, and quantity (vs BBC micro)
I was doing vacation jobs at Acornsoft at the time, and I remember the slogan that Acorn's marketing people didn't dare to use was "We've sold nearly as many computers as Sinclair has faulty ones". Sinclair sold about four times as many as Acorn, but about a quarter of them were returned as faulty. Rumour had it that the returned ones were marked with a green sticker internally, and re-sold on the assumption that it was just that the user couldn't get them working. Any returned ones which already had a green sticker were assumed to be genuinely faulty.
first pass green?
Really wouldn't surprise me if that was the case, I used to work with a bloke who claimed to have organised and tidied up Sinclair's repairs workshop, the stories he used to tell...
Sir Clive, we owe you
Started at the age of 10 with an '81, followed by a ZX-Spectrum (the "big" one, 48K) a year later which I then used for six years.
This thing started my IT career and radically changed my life and those of many others. In a parallel universe someone else would have made the first popular UK low-cost machine, but Sir Clive actually did it in ours. Bravo.
Antipodean Computing
As a youngster I had the Australian spin-off of the ZX-81 - the Z300. Sold by Dick Smith Electronics (The Australian equivalent of Maplins) it also was a Z80 based machine with a keyboard which looked exactly like the ZX-81.
16K ram and a dubious tape drive for storage. If you wanted to try out a program from a computing magazine, you had to methodically 'POKE' machine code instructions into memory via the BASIC interface. Get even one wrong and you'd wasted an hour or more of painstaking hard work.
I got through four ZX81s
I had the three dead ones up the wall, flying ducks style.
I sprayed the last one gloss white, very posh.
Also I had the Memotech 64KB memory upgrade with the beautiful anodised extruded aluminium case that hugged the back of the ZX81 and NEVER WOBBLED.
3D Monster Maze was utterly terrifying.
Memotech.....
I had a ZX-81 and wobbling rampack. and could only dream of getting the non wobbling memotech thingy.
Lots of badgering of my dad only resulted in "go get a job ya lazy bum" "but daaaaaaad its 1981 , there are no jobs"
Later on the only mometech product I got was an MTX512( who had 1 of those?) Brilliant machine, excellent quality, built to last , shame about the marketing.
Still got my one... sitting in the drawer next to me. and it works
As for the Zx81...... lost somewhere between here and my parents home...or lost forever
Best present we ever got as a kid
ZX81, then the 48k Spectrum - hour upon hour of playing games, coding, reading about, building hardware for.....
Thanks Clive Sinclair - you put me on the path that has led to a wonderful, varied IT career.....
My first was an MK14
Which I still have - drove me mad...
Then a ZX80 which arrived with faulty components, cheap diodes from memory.
After which I gave up and went the Tangerine route to 6502 heaven. Never did like the Z80 processor...
I wonder what else £49 bought then
How many Mars bars or another price stable equivalents.
Argos
This 1986 Argos catalog will give you some idea - ahhh, memories.
http://www.flickr.com/photos/38301877@N05/3593028702/in/photostream/
Hrmph
Thanks for that - I didn't have anything planned for the last hour and a half, anyway.
Looks like all my teenage possessions came from Argos...
At todays prices....
A quick search online shows the Retail Prices Index was 78.3 in 1981 - in 2010 it was 228.4.
That makes the £49 equivalent to £143 at today's prices - or the £69 pre built for about £201.
Memories - lots of them and glad to see so many of 'us' still around - also lmao at the 'old arguments' about who's was best resurfacing after all these years :D
PRINT "TITLE"
Ah, happy memories indeed! I fondly remember 3D Monster Maze with its T-Rex made up of a jumble of ASCII characters and blocks. Surely the natural fore-runner to Duke Nukem 3D and all FPS games since.
I'll raise a glass tomorrow to my long gone ZX81, strapped to a placemat with rubber bands with an empty fag packet stuffed under the 16K RAM pack to stop it wobbling. Probably one of my big brothers packets of Craven "A"s, but that's a whole different memory lane! :-)
Paris, cos err... something to do with being strapped down with rubber bands? That'll do!
well, a mate of mine
had a ZX81, and we used to go round to his house to watch him programme it or run a game on it. How sad is that? He became our acknowledged genius about technology for a while.
He quickly decided the ZX81 keyboard was too crappy and the memory pack too unreliable so he moved on to a Beeb and I got a TRS80 model 1. With a '5.25 floppy disc'. Remember them?
And we never looked back.
The thing with the ZX81 design I always thought is it looks stylish and small but is tethered at one end to the mains and at the other to a TV, making the smallness a bit pointless.
Ferranti ULAs
The ZX80 and ZX81 achieved their small size, low component count and price due to much of the necessary logic circuitry being provided by a single Ferranti ULA (Uncomitted Logic Array) on each machine. The ULA had a whole load of gates which were not connected until the final stage of manufacture - the interconnection of gates could then be determined by the customer, in this case, Sinclair.
Ferranti have long since gone but it is nice to remember that Britain produced some significant innovations.
ULA...
The ZX80 had 21 ICs inside but no ULA - the ZX81 had just four; the custom ULA in the ZX81 combined 18 generic TTL ICs from the ZX80 into a single package. The ZX80 ran hot because of all the circuitry inside and there wasn't much room internally due to all those chips, but the ZX81 was a lot cooler.
The ZX range and all the UK home computing explosion of the early 80s was at a pivotal point for the UK - it is often seen as the birth of home computing but at the same time it was the beginning of the end for many UK "hi-tech" businesses; from then an increasing amount was outsourced overseas.
The ZX81 is still used as a classic computer design in some US colleges in particular because it splits the four basic sections of a computer across the four ICs - RAM, ROM, CPU and the ULA handling the interface jobs. It's highly optimised and that demand from the colleges keeps the kit price high - in US terms, it's about the same $price as it was 30 years ago, at least on the sticker and without taking inflation into account (in the UK, kits currently fetch about £100, which is more than it cost in the beginning).
The ZX81 Lives On
It is great to see so many positive stories about the ZX81 and such enthusiasm for it in what were the very early days of home computing.
I had my first ZX81 at the age of 13 in 1982 - purchased from my brother, so he could buy a Spectrum. I too had everything screwed to a board, to stop the ram pack wobble - but then I needed something, as it had to be balanced (together with the TV) on top of my bed!
I eventually moved it into a case with a full sized keyboard, but then sold that and moved onto the Sinclair QL which was still my main machine until about 2002 when I bought my first PC!
I still support the old Sinclair computers and have daily contact with other users. Over the last few years, we have brought replacement keyboard membranes for the ZX81 to the market, and the 30th Anniversary will also see the launch of the ZXPander - a modern interface to provide both additional memory and the ability to LOAD / SAVE instantly from SD memory cards.
A lot of new software has been written over the past couple of years, much of it using hi-res graphics on the ZX81 (something that was not really achieved until about 1983/4) - see www.rwapsoftware.co.uk/zx81/zx81_software.html
The discussion forums at http://www.rwapservices.co.uk/ZX80_ZX81/forums/ are also very active, with plenty of ideas floating around and development occurring as a result.
I wonder how many people will be looking back at Windows based PCs and celebrating their 30th anniversary..... Bet no-one will be looking back in 2030 at the 30th anniversary of WIndows ME / 2000 - that's for certain!
Windows ME...
...Gah! I'd very nearly completely forgotten about that one already, Rich. Now I'm going to have to start working to forget it all over again!
Mines Still Boxed Up
In the loft, as is my Dragon 64, sadly both are 4000 miles away from where i currently live :(
ZX81 Video circuitry
Steve the cynic is basically right, there was no dedicated video circuitry. There wasn't an FPGA either, there was a custom logic chip (made by Ferranti?) which replaced a bunch of standard logic chips that the ZX80 had, reducing the chip count from I believe 21 to 4 (or 5 on some units). There was some sort of hardware modification in the logic chip to allow slow mode, that would not work on a ZX80 with the ZX81 rom upgrade.
The video was generated with the help of the DRAM refresh cycle built into the Z80 microprocessor, this wasn't needed as the computer used static ram (1x 1K or 2x 512byte).
The refresh cycle was set up by sortware at the start of each scanline to generate addresses to read the screen data, the logic chip kept the Z80 executing NOPs (No OPeration instructions) for the duration of each line by basically shorting the data lines to ground.
Lots of use and abuse of the components, but they made a working computer system using just 4 chips all the way back then, and it was affordable. Within its rather tight limits (it was cheap) it was a very capable little machine.
You didn't mention the manual. The manual was awesome, it started right at the start (it had to, most owners would never have used a computer before), introduced more concepts as you read through, working up to documenting many of the inner workings. My favourite page is where it introduces the concept of variables by using the rapidly increasing price of eggs!
Ahhhhhh. The memories......
My First ever computer. Badgered my dad for one for ages in the run up to christmas. First computer I ever owned/programmed/tinkered with.
This was the computer that launched my interest into all thing computers and gadgets and ultimately launch me in a career in I.T.
Still got a couple in my collection along with one of every Spectrum Model (including the resonably rare 16k Spectrum (fully boxed)).
I also had an Acorn electron and then a BBC model B. Those were the days...........
Of cours these days I still run emulators to play the old games for these computers and tinker with programming.
I shall lift as pint or two tonight in celebration.
Happy memories
Christmas 1981 what a great moment for a 11 year old.
After 6 months hanging around in WHSmiiths staring at it and begging my parents.
Ah I can still vividly remember the absolute thrill and joy as I pulled the polystyrene packaging from the cardboard sleeve. Looking at the pictures, I can still remember the smell of it for heavens sake!
Then Christmas day spent typing in the first programs from the manual. Something about the price of oranges I seem to remember.
What a major pivot point in my life. 30 Years on and I've got kids of my own and we're living a great life style. In no small way, thanks to that little black box.
Sir Clive and everyone involved - Thanks from the bottom of my heart!
ps I have a 4 year old daughter who is teaching her two year old sister how to play cartoons on our old iphone. I wonder if they will have similar memories?
This topic is closed for new posts.
