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The Sinclair ZX81 or Timex Sinclair TS1000 ROMs

There are multiple versions of the ZX81 ROM. The ROM of the ZX81 and Timex1000 are the same. Differences between the machines, e.g. TV frame rate, are performed in software based on a PCB jumper.

The 'standard' ROM

The original, buggy, first version of the ROM as shipped by Sinclair.

The 'improved' ROM

The debugged 2nd version of the ROM as shipped by Sinclair.
The disassembly by Dr. I. Logan & Dr. Frank O'Hara was taken from Kryten's web site (no longer online).

The 'Shoulders of Giants' ROM

This is a debugged variant by Geoff Wearmouth www.wearmouth.demon.co.uk/.

Other Languages

There were several replacement ROMs available which provided different programming languages as the default powerup language: Two Forth ROMs and a Z80 assembler OS, the Aszmic ROM. The latter was only 4 kB, so i believe that it also worked for the ZX80.


Some clones had slightly modified ROMs. Currently archived are the Lambda and the Power8300 ROMs, though these machines were just differently named and otherwise identical clones.

ZX81 fans kept on working with their machine and built improved versions, which used enhanced ROMs. The ZX97 ROM is a result of these efforts. It doesn't suit the original ZX81, e.g. it is 32 kB in size.

These ROMs were copied from various sources, e.g. from Nils Eiler's homepage home.germany.net/nils.eilers/zx81/ de.gif.


Name Letzte Änderung Länge 
Skywave Forth Rom/ 2008-09-14 16:11
aszmic (z80 assembler os).rom 2005-11-14 09:32 4096 
h4th (Forth).rom 2005-02-27 18:09 8192 
Lambda (org) (zx81 clone).rom 2005-02-27 18:09 8192 
Power8300 (org) (zx81 clone).rom 2005-02-27 18:09 8192 
tree4th (Forth).rom 2005-11-14 09:33 8192 
zx80.rom 2002-02-23 12:14 4096 
zx81 'shoulders of giants' rom source.html 2005-10-27 19:21 139466 
zx81 'shoulders of giants'.rom 2003-05-09 23:49 8192 
zx81 sysvars.pdf 2012-10-01 19:46 19372 
zx81 version 1 'standard' rom (Sinclair).rom 2001-11-27 07:14 8192 
zx81 version 2 'improved' rom (Sinclair).rom 2005-11-14 09:31 8192 
zx81 version 2 'improved' rom differences.htm 2001-12-11 08:53 42862 
zx81 version 2 'improved' rom disassembly (Logan, O'Hara).html 2005-11-07 08:59 291062 
zx81 version 2 'improved' rom source.htm 2005-10-29 18:23 417753 
zx81 version 2 'improved' rom source.txt 2014-10-18 17:36 373053 
zx97 32K enhanced ROM for an enhanced ZX81.rom 2005-02-27 18:09 32768 
Das ROM des ZX81 283 

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