Setname:  zx81   
Year: 1981
Manufacturer: Sinclair Research Ltd
Status: good  works
Type: Home Computer
Clones: Lambda 8300,
Power 3000,
Ringo 470,
Timex Sinclair 1000,
Timex Sinclair 1500,
Emulation info
Overall emulation:  good   
Color emulation:  good  
Sound emulation:  good  
Graphics emulation:  good  
Savestates:  unsupported   

Tech info
Z80 ("maincpu")cpu 3250000 Hz
Speaker ("mono")audio
Filtered 1-bit DAC ("speaker")audio
Wave ("wave")audio
Screen ("screen")raster horizontal 256 x 304 @ 50.652245
Media devices
cassette ("cassette") cassette cass wav, p, 81
BIOS options
3rd 3rd rev.
1st 1st rev.
2nd 2nd rev.
hforth Forth by David Husband
tforth Forth by Tree Systems
RAM options
1K 1024
16K 16384

Show detailed info about 'Configurations' of this system

TV system NTSC

Romset info
ROM NameSizeCRC32SHA1Dump StateBIOS option
zx81.rom8192 fcbbd617a0ade36540561cc1691bb6f0c42ceae12484a102good1st
zx81a.rom8192 4b1dd6eb7b143ee964e9ada89d1f9e88f0bd48d919184cfcgood2nd
zx81b.rom8192 522c37b8c6d8e06cb936989f6e1cc7a56d1f092da854a515good3rd
h4th.rom8192 257d5a3203809a6b464609ff924f7e55a85eef875cd47ae8goodhforth
tree4th.rom8192 716162383ee15779e03482b10fc59eb4df2446376c56b00dgoodtforth


* CPU: Zilog Z80A 3.5 MHz
* RAM: 1 KB (901 bytes available, up to 64 KB)
* ROM: 8 KB
* Text Modes: 32 x 24 (but 2 lines are reserved for system messages and commands)
* Graphic Modes: 64 x 44
* Colors: Black and white
* Sound: None
* I/O Ports: Z80 Bus, tape, video
* Keyboard: Touch-sensitive keyboard, 40 keys
* Built In Language: Sinclair Basic


MESS emulates the following computers

* zx81 [Sinclair ZX-81]
* ts1000 [Timex Sinclair 1000]

For both drivers, MESS supports the emulation with a "cassette" (cass) device, for tapes in .wav, .p and .81 format.


These systems require full keyboard emulation to work correctly. At startup, full keyboard emulation mode is enabled by default. Whilst in full keyboard emulation mode, some key associated functionality may be disabled (like the ESC key for EXIT). The keyboard emulation mode is toggled using the "Scroll Lock" key (by default).

BIOS options

MESS supports various revisions of the ZX81 bios. You can switch between them, changing the -bios parameter. At command line,

"-bios 0" or "-bios 3rd" = 3rd rev.

"-bios 1" or "-bios 1st" = 1st rev.

"-bios 2" or "-bios 2nd" = 2nd rev.

"-bios 3" or "-bios hforth" = Forth by David Husband

"-bios 4" or "-bios tforth" = Forth by Tree Systems

hforth and tforth options emulate a zx81 with swapped ROMs to use Forth instead of BASIC, as programming language.

RAM options

Different RAM configurations are possible for these systems in MESS. You can switch between them, changing the -ramsize parameter. At command line, you simply have to add ''-ramsize ram_value'', where //ram_value// can assume one of the following values

1k (default)

Known Issues

The emulation of this system is currently Not Working.

History and Trivia

A home computer built in the United Kingdom.

The Sinclair ZX 81 was the successor of the ZX 80, and can be regarded as an evolution of it.

The ZX80 could not handle floating point numbers or cassette data files, but the ZX-81 could. The ZX-80 had 4k ROM : the ZX-81 had 8K ROM with 30 additional functions and some instructions to drive the printer. Thanks to a higher level of integrations (the total number of chips in the basic system was 4, against the ZX80's 21), the ZX-81 cost £30 less than the ZX-80. The plastic case was also different. Whereas the ZX-80 looked cheap in it lightweight white case, the ZX-81 was beautifully designed in its black ABS plastic case.

The keyboard was still formed by an underprinted plastic, but this one was made of non-reflective material. Even with this slight improvement it was quite horrible to use, that's why a lot of additional keyboards appeared quickly on the market. Some of the keys sported up to 5 functions, right in the Sinclair tradition, accessible through the "GRAPHICS", "SHIFT" and "FUNCTION" keys.

Here are the functions added over the ZX-80 : ASN, ACS, ATN COS, EXP, INKEY$, PI, SGN, SIN SQR, INT, LEN, LN, TAN, VAL, <=, >=, < >, COPY, DIM A$, FAST, FOR ... TO ... STEP, LLIST, LLIST n, LPRINT, PAUSE, PLOT, PRINT AT, PRINT TAB, SCROLL, SLOW, UNPLOT. Some are quite useful and make you wonder how it was possible to make anything on the ZX-80 !? However, one function disappeared: TL$ which was used to return a string minus its first character.

The ZX-81 could be operated in two modes, SLOW and FAST. The FAST mode which was the only mode available on the ZX-80, only refreshed the display when the system had completed computing, resulting in a painful screen flicker! It was a useful mode when you had to do a lot of calculation without the need to see what's going on all the time on the screen. The SLOW mode, which was indeed quite slooooowwww, behaved like all other computers did, refreshing the screen all the time.

The ZX81 contained only four main chips : the ROM, Z80A CPU, 1K RAM and the Ferranti custom-made chip! It is as simple as that. The machine was assembled by Timex Corporation in their Scottish plant.

This computer was a very great success in Europe in the beginning of the 80's. It was very cheap and a lot of people who now are working on modern PCs or Macs, made their first move on a ZX 81 even though its performance was actually poor!

A very great range of peripherals were developed for this computer, among them : 3.5" floppy disk units, keyboards, high resolution graphic cards, RS232 or Centronics interfaces, RAM expansions, etc... In fact, it was possible to make a pretty good computer from the ZX 81!

It was followed by the ZX-Spectrum and was also sold as the Timex Sinclair 1000 in the USA. The main difference was that the TS 1000 has 2 KB RAM instead of the 1 KB RAM of the original ZX-81.

(info from old-computers.com)


* Achromic's ZX81 Page -- http://zx81.achromic.co.uk/
* Jame's Sinclair ZX-81 Page -- http://james.istop.com/zx81/
* Planet Sinclair -- http://www.nvg.ntnu.no/sinclair/computers/zx81/zx81.htm
* TS1000.US -- http://www.ts1000.us/
* ZX81 Stuff -- http://www.zx81stuff.org.uk/
* ZX81 Home Page -- http://www.honneamise.u-net.com/zx81/
* ZX Team -- http://www.zx81.de/
* ZX81 at old-computers.com -- http://old-computers.com/museum/computer.asp?c=263

Other Emulators

* VB81 -- http://freestuff.grok.co.uk/vb81/
* XTender -- http://www.delhez.demon.nl/
* No$ZX81 -- http://www.work.de/nocash/zx8.htm
* EightyOne -- http://www.chuntey.com/eightyone/

Edit the History info for this game.


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