This page is sponsored by

(The ZX81 Support Page)

The site for the ZX-81!

Welcome to this new support forum for all 16KZX81/TS1000 enthusiasts everywhere!

"The Sinclair ZX81 Support Page" was maintained by Steven McDonald but is sadly no longer updated (very much)!

I provide an archive here for reference purposes only! (I don't have the time anymore... Sorry!)


Last Update: Saturday, 31st Dec, 2011.

"Whatever else you do, keep using the computer. If you have a question 'What does it do if I
tell it such & such?' then the answer is easy: type it in & see. Whenever the manual tells
you to type something in, always ask yourself 'What could I type instead?' & try out your
replies. The more of your own stuff you write, the better you will understand the ZX81.
(This is called unprogrammed learning.) Regardless of what you type in, you cannot damage
the computer."

From ZX81 BASIC Programming, Second Edition
By Steven Vickers
(c) Sinclair Research Limited, 1980


zx81small.gif (8053 bytes)

- Why The Fascination? -


In case you are reading this and thinking to yourself, "what on earth is a ZX81", either because you never heard of it or were not born at the time, then read on...

Another question often asked is, "why the fascination with that old computer?". Well let me try and explain...

The ZX81 was the successor to the ZX80 and one of the cheapest home computers. Sinclair was able to make huge manufacturing savings by the inclusion of a custom Ferranti ULA or "glue chip" that connected the other components together in a way that made them do more than they otherwise would.

This ULA was responsible for the ZX81's low chip count. Other things like the cheap membrane keyboard used also kept costs down. In the UK, it was the first sub 100.00 computer - cheaper than its predecessor and more powerful to boot!

The chips consisted of a Z80 A CPU (clocked at 3.5Mhz), an 8KBASIC ROM, 1KB RAM and the ULA. There was no graphic chip; the CPU had to do the job! This was actually a major plus point for clever programmers, as it gave them total control over how the TV display was generated. Sir Clive himself once said that High Res was impossible...

I often wonder if he ever knew about what was achieved with his machine in later years?

The ZX81 was sold retail and as a DIY kit back in 1981 and thousands of them were sold at the time. A 16K memory expansion pack that connected directly onto the expansion bus (prone to wobble) was available that boosted its capacity for serious applications.

Programs were stored on tape through the cassette interface operating at a slightly slow 300Baud and a special thermal ZX printer was also available.

Clever software was later written to LOAD and SAVE from tape at vastly increased speeds and to print out on the ZX Printer in High Res.

Over the years many hardware experts have come up with interesting add-on projects for the ZX81. Back in the 80's, I kept in contact with a great guy and clever programmer, (Fred Nachbaur) who actually had a disk drive interface for his ZX81! Devices such as High Res colour graphics boards, sound cards, SCRAM memory boards, replacement keyboards etc. were available from enterprising companies.

People such as Wilf Rigter, Kevin Baker, Kai Fischer, Peter Liebert-Adelt and The German ZX-Team are still very much active!!! In addition, here at the end of the 90's, many ZX81 enthusiasts are using the Internet to stay in touch, help each other out and to share their ideas and projects. Indeed, Wilf Rigter continues to develop designs for a portable ZX81 for the 90's complete with LCD screen etc.

So what is it about this machine then?

Well, it was a lot of people's first computer and had an excellent manual that introduced you to its BASIC programming language. After that you could progress to programming the machine in Z80 assembler, if you fancied, that gave you full control over the machine at every level!

I think that it is this power over the machine and the ZX81'sinherently simple but extremely clever design that made it so attractive.

Although technically, its successor, the ZX Spectrum was far more advanced, featuring colour displays and sound, to me it just wasn't as exciting a machine because you couldn't take direct control of the tv picture generation for example!

These are the things that make this machine stand out from the rest and to this day you can still buy ZX81 kits on the Net and build for yourself this most rewarding little computer.

The ZX81 is an excellent machine to learn about the basics of computers on and the principles learnt can still be applied to current computing in the90's!

Above all, the ZX81 was a computer you could experiment with and try things out on! The paragraph from the ZX81 manual quoted at the start of this page is my favourite from any computer manual I have ever read, as it encourages you to not take things for granted and to figure things out for yourself. When I was starting out on computers, this was a great philosophy to follow and today I would say that everything I know about them goes back to this excellent advice from Steven Vickers in that book!

So even if you have an all-singing, all-dancing Pentium II300Mhz multimedia computer, you could still learn a thing or two from the old SinclairZX81! So why not try out some of the emulators or programs available here.

There are a few PC ZX81 emulators out there but none come even close to matching the realism of Carlo Delhez's excellent XTender2 - now in Beta testing.

If you still own a ZX81, get it down from the attic and dust it off and be prepared to be surprised at what can still be achieved with it!

zx81small.gif (8053 bytes)

- Technical Description -

Computer: ZX81
Manufacturer: Sinclair Research Ltd.
Released: 1981
CPU/Clock speed: Z80A clocked at 3.5 MHz
RAM (Expandable): 1 (16) Kbyte
Screen: TV (50 or 60Hz)
Text mode: 32*24
Graphics mode: 64*44
Colors: Black/White
Sound: None
Keyboard: Membrane Keyboard (40 keys)
Interfaces: TV, Earphone, Microphone, Expansion Bus
Size (in mm): 167*175*40



- Rock Crush 2011 Rewrite Now Available! -

31st Dec, 2011.


Rock Crush has been re-written!!! A pixel perfect ZX81 version is now available for the iPad! Get it here

Written by the original author - it is an authentic version of the game with many new features if you want them!

PC, Mac and iPhone versions are coming!!!

- Rock Crush eBook Now Available! -

20th Feb, 2011.

irst update to this page in ten years! The time was right for the release of some documents - 25 years after the event! Detailing the writing of Rock Crush - A high res ZX81 game! Click here to get your copy!

- The Page Lives!!! -

13th Nov, 2001.

Greetings fellow enthusiasts! The page is back up on yet another new server! Thanks to for sponsoring this page!

Please bear with me at the moment - there is much to be fixed on this page!!

In the meantime, I will say that if you need to contact me - send an email to and nowhere else! It will reach me.

I felt it was more important to get this page back up than to fix everything that's wrong in one go.

The address is not updated yet. The ZX81 survey link should not be used. Some links are broken.

Bear with me - I will get there!

So what's new?

Well... I can now present the first update to this site in around two years!

Click below for the exclusive new Software Farm Tribute Page - complete with downloads - I haven't seen 'Spectrumiser' or 'Booster' featured anywhere else!

Visit the Software Farm Tribute Page


- Update To Fred Nachbaur's Page! -

14th Feb, 1999.

Fred's been busy lately, converting over more of his files. Take a look below at this rather large update! Thanks, Fred!

- Fred Nachbaur's ZX81 Page Just Launched! -

21st Jan, 1999.

I've been in constant touch with Fred Nachbaur, since his 'arrival' back on theNet... He had been away totally from computers for over 10 years butis catching up fast on the latest developments. I remember when I did a similar thingback in the early 90's for a few years. Things move so fast... I was like,"Windows... What's that?".
Anyway, Over the past week or so he has been very busy raiding his attic andconverting all his old software over to the PC (using ZXD!). After discussing this ideawith Fred, he was more than happy to document and make available his treasure trove ofprograms.
On this page, exclusive to Tech/Worlde you can now rediscover all these gems. Fred'sin charge here so look forward to updates... Link at the main menu below as usual!


- Updated Release of ZX81 Converters! -

18th Jan, 1999.

I have just finished putting the final touches to Release 3.0 (final build). Many newfeatures and bug fixes. Grab it from the usual place below. Special thanks go to FredNachbaur for all his real life testing and feedback on V2.0!


- Fred Nachbaur Contacted! -

11th Jan, 1999.

It was great to hear from the one and only Fred Nachbaur the other day - Last I heardfrom Fred was way back in 1988... Fred wrote some of the most technically advanced softwarefor the machine I can remember, using Wilf's hi-res system and the good old SCRAM boardwhich he was happy to ship over the pond to me back then...

He wrote:

"Hi Steven,

It was a delight to find your ZX81 home page. At one time I was quite involvedwith the machine, to the point where I _almost_ made a living writing software for it (Ihad a very low overhead at the time ;-)

Anyway, there are a couple items: Any of my programs may be freely posted,circulated, done with however/whatever, as I have put the entire catalogueinto the publicdomain. The two most significant programs were "Dungeon of Ymir" (apretty fancy D&D game) and "ZX*TERM*80" (a BBS terminal programfeaturing 40, 60, even 80-column screens). Both used Wilf Rigter's WRX16 (SRAMbased) hi-res system.

The web sure is a funny thing... you might find this unbelievable, but theway I found your site is by entering _my_ name in a search engine (ego curiosity, I guess)and one of the things it came up with was a reference to me by Wilf which pointed to yoursite! Bizarre, isn't it?

You wrote some of the finest software for the little machine, and I'mreally flattered that you still have the stuff I sent
"way back when." When I wrote to you I wasn't sure if you were _The_ StevenMcDonald... heh, heh. So I thought I'd play it safe and keep it low-key.

I'll have to take a good look through your site and the others you linkto, to see what's involved with converting ZX files to work on the emulator. (This is awhole new field for me... When I packed away my Sinclair stuff, I basically didn't touch acomputer for some ten years, and am just now getting back into things.)"

Well, welcome back Fred!! It's been a long time...

Fred later let me know that he had Rock Crush up and running on his 486...Great to hear.

It would be great to see Fred's ingenious software up and running aswell... He really knew how to push the machine to its limits and sometimes even beyond...

In the future, I plan a page here to show off Fred's work...

In the meantime, why not check out Fred's very interesting website and seewhat he's up to... or


- XTender2 Moves To BETA 6! -

2nd Jan, 1999.

Just released at the tail end of 1998, Carlo Delhez has released Beta 6 of XTender2!This build features minor bug fixes and extends the testing phase. Read below for the linkto Carlo's site.

- V2.0 RC1 ZX81<=>PC Converters Released! -

28th Dec, 1998.

I have finally bowed to pressure and all the requests to release this! I am pleasedto announce you can now download my ZX81<=>PC Converters. This is release candidate1 (of version 2.0) and is available at the usual menu below.


- XTender2 In BETA Testing -

24th Sept, 1998.

There have been a number of exciting developments in the pastyear or so and I will cover them all in due course...

The biggest news is that Carlo Delhez - author of 'XTender' haswent back to the drawing board and is currently writing XTender2. It is free for testingat the moment during the Beta development stage. The latest build is Beta 6 (Dec. 98) andis available now at Carlo's excellent new homepage at:

XTender2 is a "2nd generation" emulator from Carlo and issuperior to XTender in all respects. The price you pay is that it requires a Pentium133Mhz or better processor to run smoothly. If you have less than this, you can still runthe original XTender which flies even on XT/AT/386 and 486 systems. XTender is a sharewareproduct and has many thousands of devoted users. You can get full details at his siteabove.

Major Features In XTender2 Include:

new.gif (641 bytes) Emulates manydifferent systems, for example ZX80, ZX81, Aszmic, PC-8300, or even a user-developedsystem.

new.gif (641 bytes) Full low-levelemulation of ZX80/ZX81-compatible hardware, in particular including the complicated videosystem (ULA 'nop-logic') at T-cycle accuracy, with numerous user definable settings suchas PAL/NTSC video, physical memory allocation, memory shadow modelling.

new.gif (641 bytes) NMI-generator control, ULA-accesscontrol.

new.gif (641 bytes) Runs any hi-res, semi-hi-res, mixedresolution, and low resolution ZX81 program.

new.gif (641 bytes) Can run ZX81 programsdirectly from the DOS commandline, or by double-clicking a P-file in Windows9x/NT (so youdon't have to type a LOAD "..." command inside the emulator).

new.gif (641 bytes) Can load & save ZX80 programsfrom & to disk in O-files.

new.gif (641 bytes) Supports both SLOW and FAST mode, andalso intermediate modes (as generated by specific tools).

new.gif (641 bytes)Very realistic video output - not seenbefore on any other ZX81 emulator  - because XTender2 includes a TV-emulator: your PCmonitor responds like a real TV-set when the ZX81 does not provide proper video timing(this happens in FAST-mode, for example). XTender2 lets your screen flicker, flash,tremble and roll, very similar to what you would see on the real thing!

new.gif (641 bytes) Provides an excellent keyboardinterface. The keyboard will never lock, multiple simultaneous keypresses are possible,and even keyboard matrix errors are emulated correctly! Supports PC-keyboards with QWERTY,AZERTY and QWERTZ layout.

new.gif (641 bytes) Produces graphical printer output.

new.gif (641 bytes) Includes a virtual tape interface:save/load your data to/from a virtual tape recorder and watch the tape signals beingechoed to the screen! The virtual tape interface is the ultimate method to get data intoand from any system (including ZX80, ZX81 and Aszmic) and/or by any original (fast)Save/Load tool  that you ever may have used. Original tape recordings can beconverted to virtual tape files, and vice versa.

new.gif (641 bytes) Has a very flexible interface to the"outside world" via non-intrusive user-definable ROM-patches that are fullyinvisible for the emulated system (PEEK, etc.) and that are handled by external programs(i.e. not by XTender2 itself).

new.gif (641 bytes) ...and lots of interesting newfeatures still to come!  Just wait & see!

Carlo is doing an outstanding job on this project - it really is mind blowingstuff!

I have used many emulators over the years both computer emulators andarcade game emulators etc. and I can say that nothing touches the realism builtinto XTender2! It features something totally unique - a TV emulator - so your monitorpicture actually jumps up and down in FAST mode etc. exactly like the real thing!

There are other ZX81 emulators out there, some of which are really goodbut the bottom line is nothing comes close to the realism of XTender2 (or will).

I have a future page planned that will cover XT2 including custom scriptsand setting up XT2 for running certain programs etc.


- New Updated Site Layout -

24th Sept, 1998.

The Sinclair ZX81 Support Page has been restructured and a new site layoutrevealed! The main 'page' had been growing far too big and was taking a while to downloadas a result! I also needed to plan for the future and bring about some order to this site!The result is the new Site Menu showing all the sub pages available from here. Some of thisis still work in progress but at least it is a better way to organise things!

There is a shortcut to the Menu from the very start of this page - just click on The site for the ZX-81! and youwill be taken there instantly!

From now on, the main page will feature all the latest news andinformation on the ZX81. As time progresses, the older stuff will be taken down from thispage and posted into the News Archive to free up room here.

I hope you like the new layout!


- The Sinclair ZX81 Support Page Relaunch! -

17th Sept, 1998.

Finally, after 18+ months of being pulled from the Net, this sitehas been re-launched! It was not my intention for it to be down this long but due to awhole catalogue of problems, it was not possible for the site to be published as it was,on Tech/Worlde.

So the good news is, this site is back and here to stay! All the code hasbeen converted over to FrontPage 98 with the result that site maintenance will be mucheasier! (I was previously hand coding the HTML.)

Please bear with me during this changeover phase, as I get around toupdating everything!



The Sinclair ZX81 Support Page Menu:


zx81small.gif (8053 bytes)

As this site has grown over time, the mainpage had started to get too big!
In order to combat this and bring some order to this site, things have beenrestructured as detailed below!

I hope you like the new layout.


ZX81 News:

ZX81 News Archive

Steven McDonald's Software:

Free High Res Games - 'Rock Crush' And 'Dans Revenge'
AUTOREM - Machine Code Storage
ZX-FILE 2.0 - Fast Tape OS
16K ZX81 Ramdisk Operating System (ROS)
N E W * * * ZX81<=>PC Converters V3.0 * * * N E W

ZX81 Support:

ZX81 Survey And Free ZX81 Mailing List Service
ZX81 Users Contact Forum
ZX81 Guest Book
Details On The Jack Raats ZX81 Listserver

ZX81 Hardware:

Wilf Rigter's Column
ZX81 Kits For Sale in 1999!
Enrico Tedeschi's Book - 'Sinclair Archeology'

ZX81 Software:

N E W * * * Fred Nachbaur's ZX81 Page * * * N E W
Author's Personal ZX81 Software Library
The XTender2 Page
Other ZX81 Emulators

ZX81 Programming:

The Secrets Of Pseudo High Res Display Generation
Z80 Machine Code Programming On The ZX81
ZX81 Magazine Programs To Type-in


Note: Links in BLACK are still under construction at this time.

ExternalZX81 Site Links:

Carlo Delhez's XTender - ZX81 Emulator Site

ZX81 Home Page

ZX81 Software

Paul Robson's ZX81 Emulator

Kevin Baker's ZX81 Site

Mathew's ZX81 Homepage

James' Sinclair ZX81 Page

Planet Sinclair



- As Yet Unreleased ZX81 Software! -


The following items are planned for the future . . . (and may arrive inany order!)

1/. New versions of Rock Crush and Dan's Revenge - V3.0 (to run at thesame speed on all cpu's and improve performance on XTender). I also plan a V4.0 for usewith XTender2 only. I have had to 'tweak' my games over the different versions to optimiseperformance with XTender. XTender2 is capable of running the original code exactly as itwould on a real machine - so with V4.0 it will be back to the original codebase but withupdated documentation etc.

2/. Future project - my new ZX81 O/S ported over to XTender. I have buildsworking for XTender which have been specially 'tweaked' to work correctly. The originalcodebase works fine with XTender2, I am glad to report - even the interrupt drivenflashing cursor routine! Once I have documented this lot, expect a release!

3/. ZX-FILE 2.0 - an extremely fast crash-proof Turbo Tape Filing System!I have this ported over already and it works bug free with XTender2. It really is amazingstuff to watch on your PC monitor!

4/. My personal ZX81 Software Library - a lot of goodies will be posted uphere! For copyright reasons, you must actually own the original before using it on anemulator or a real ZX81!

5/. The results of the ZX81 survey and action on what you are all after.

This little lot will obviously keep me very busy, however I know there is still a lot ofinterest in this amazing little machine and there is still plenty of life left in it yet!

This site will be kept up to date with all the latest newsand views from ZX81/TS1000 users from around the world!

Please feel free to send in any questions, advice, commentsor news you may have.

Long live the ZX81!


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