JtyOne Online ZX81 Emulator

JtyOne Online ZX81 Emulator

The JtyOne emulator is a JavaScript port by Simon Holdsworth of Mike Wynne's original EightyOne emulator. The emulator covers all of the functionality of the ZX80 and ZX81, including accurate timing of the display update to support the high resolution graphics tricks some programs used. In this JavaScript version I've streamlined the loading process and added a touchscreen keyboard.

The Java Emulator: You can also still download the original Java emulator.

Loading: The emulator can load a program via URL parameters or using the buttons below, otherwise you get a new ZX81 on which to write and run programs (but not save!). If you know the name of the .p file you can also load it directly, for example LOAD "3DMONSTERMAZE" or LOAD "MAZOGS".

Speed: Use the buttons to change the size of the display and speed up or slow down the emulator. When running at normal speed the ZX81 should display 50 frames per second (FPS). If the FPS does not increase when you speed up the emulator then its running as fast as it can. For iPads 66% is the best speed to run, other devices may require slower speeds.

If you have enjoyed the site, please consider a donation towards preservation of more items:
It appears your browser does not support the canvas element so no emulator is available.

Using the emulator

The emulator behaves exactly as a classic ZX81, including the keyboard. When using the emulator with a real keyboard, some keys are mapped for convenience, including the backspace key, cursor keys and some punctuation.

You can also use the on-screen keyboard with a touch device. In that case the shift key acts as a toggle, press it once and then a key to get the shifted character; press it twice to lock the shift on, and again to release it.

After loading a program you can LIST it or RUN it. A few programs have more complex ways to run, for example ones which use high resolution graphics. The instructions for those can be found in the instruction or inlay scans.

For more information about how to use the ZX81, there is an online version of the ZX81 Basic Programming manual.


The Javascript version of Jtyone was converted from the original EightyOne emulator which includes code by Mike Wynne and Philip Kendall. The emulator uses adapted versions of js-unzip and js-inflate to access TZX files within ZIP files.

Use on Other Web Sites

The emulator can be used subject to the following license:

/* JtyOne - A JavaScript ZX81 emulator.
 * Translated from EightyOne  - A Windows ZX80/81/clone emulator.
 * Copyright (C) 2003-2006 Michael D Wynne
 * Java translation (C) 2006 Simon Holdsworth
 * JavaScript translation (C) 2015 Simon Holdsworth
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * GNU General Public License for more details.
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

The original JtyOne Java emulator

You can run the ZX81 emulator outside of a web browser as an application using jtyone.jar (pesky antivirus programs may likely warn you about downloading .jar files). Run the emulator by clicking on the JAR file icon or by running it from a command line. The command line supports some additional options:

java -jar jtyone.jar 
   [tzx file name[@track number] ]
   [-scale screen size multiplier]
   [-hires {qs|dk}]
   [-machine {ZX81|ZX80}]

For example:
java -jar jtyone.jar 10Games.tzx@3 -scale 3

The file must be a .tzx file or .tzx.zip file, like the ones available on this site. The emulator doesn't load individual .P files.

The source for the JtyOne emulator is available under the GPL, as required by the EightyOne source. You can download it from here.