About PCjs

The PCjs Project is a collection of computer simulations written in JavaScript. It is an open-source project maintained and hosted on GitHub as pcjs.org (formerly jsmachines.net).

The goals of the project are to create fast, full-featured simulations of classic computer hardware, help people understand how these early machines worked, make it easy to experiment with different machine configurations, and provide a platform for running and analyzing old computer software.

The simulations are written entirely in JavaScript and run well in a variety of web browsers, on both desktop and mobile devices. Machines are created with simple XML files that define a set of machine components, along with the features that each component should enable. More details about machine definitions and component capabilities can be found in the Documentation.

Simulating the Challenger 1P

The first PCjs simulation was C1Pjs, which emulates the Challenger 1P, a 6502-based microcomputer introduced by Ohio Scientific in 1978. C1Pjs v1.0 was released in July 2012. More information about the first release of C1Pjs was posted on the OSI Discussion Forum at osiweb.org.

Simulating the IBM PC

The next PCjs simulation was PCx86, which emulates the original IBM PC, IBM PC XT, and IBM PC AT. PCx86 v1.0 was released in late 2012. Browse the source code here or on GitHub.

PCx86 emulates the Intel 8088, 80186, 80286 and 80386 CPUs, as well as IBM Monochrome Display Adapter (MDA), Color Graphics Adapter (CGA), Enhanced Graphics Adapter (EGA), and Video Graphics Array (VGA) video cards, along with assorted motherboard and expansion bus components. It also includes an optional Debugger and a user-configurable Control Panel.

Read About PCx86 to learn more about its history, features, and upcoming improvements.

Migrating to Node

The PCjs web server was originally written in PHP and hosted by DreamHost as jsmachines.net, but in 2014, it was migrated to a Node.js web server and hosted by Amazon Web Services as pcjs.org.

The goals included:

  • Using JavaScript exclusively, for both client and server development
  • Leveraging the Node.js web server to provide more sophisticated I/O capabilities
  • Improving overall website design, including structure, appearance and responsiveness

The PCjs Node web server includes a number of custom Node modules that provide many of the same server-side features found on jsmachines.net, including new ROM and disk image conversion APIs, and a Markdown module that supports a subset of the Markdown syntax, including extensions to the link syntax that make it easy to embed PCjs machines in Markdown documents.

Migrating to GitHub Pages

To simplify hosting requirements, the PCjs Project was migrated to GitHub Pages in late 2015. The project still includes the original Node-based web server, which is useful for development and debugging, but for production sites (including pcjs.org), using Jekyll to generate a static copy of the project for the web is the preferred solution.


The PCjs Project is now an open-source project on GitHub. All published portions are free for redistribution and/or modification under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

You are required to include the following copyright notice, with a link to pcjs.org:

PCjs © 2012-2017 by Jeff Parsons (@jeffpar)

in every source code file of every copy or modified version of this work, and to display that notice on every web page or computer that runs any version of this software.

See LICENSE for details.

More Information

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