The original IBM PC and other machines (x86, 8080, 6502, PDP-11) emulated in JavaScript
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PCjs Machines

Welcome to PCjs, home of PCx86, the original IBM PC simulation that runs in your web browser. It is one of several JavaScript Machines in the PCjs Project, an open-source project that includes:

All PCjs machine simulations are written entirely in JavaScript. No Flash, Java or other plugins are required. Supported browsers include modern versions of Chrome, Safari, Firefox, Internet Explorer (v9.0 and up), Edge, and assorted mobile browsers.

Embedded IBM PC

The JavaScript Machine above uses PCx86 configured with an Intel 8088 running at 4.77Mhz, with 64Kb of RAM and an IBM Monochrome Display Adapter. For more control, there are also Control Panel and Soft Keyboard configurations, featuring the built-in PCx86 Debugger. For even greater control, build your own PC. The PCx86 Documentation will help you get started.

PCx86 has steadily evolved to support more classic x86-based machines, including the IBM PC XT, the 80286-based IBM PC AT, and the 80386-based COMPAQ DeskPro 386. PCx86 fully supports the original machine ROMs, video cards, etc, and all machines run at their original speeds.

The goals of the PCjs Project 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.


Some pre-configured machines are shown below, ready to run BASIC, DOS, Windows, OS/2, and other assorted software.

IBM PC running VisiCalc IBM PC running DONKEY.BAS IBM PC AT w/EGA, OS/2 1.0 IBM PC XT w/CGA, Windows 1.01 IBM PC XT w/EGA, Windows 1.01 COMPAQ DeskPro 386, Windows/386 IBM PC AT w/EGA, Windows 3.00 IBM PC AT w/VGA, Windows 3.10 COMPAQ DeskPro 386, Windows 95 IBM PC w/MDA, CP/M-86 IBM PC w/MDA, Microsoft Adventure IBM PC w/CGA, Zork I

There are many more PCx86 Demos, including an IBM PC with Dual Displays demonstrating early multi-monitor support, and multiple IBM PC XT machines running side-by-side with CGA Displays and EGA Displays.


Below is the OSI Challenger C1P, another simulation in the PCjs Project. It simulates Ohio Scientific's 6502-based microcomputer, released in 1978. More details about this simulation and the original machine are available in the C1Pjs Documentation.

Embedded OSI Challenger C1P

Developer Notes

The PCjs repository on GitHub contains everything needed to run PCjs computer simulations. All the PCjs emulators run in any modern web browser, with or without a web server, and examples are provided for both local and remote operation.

The project includes:

The bundled web server is not strictly required. Any web server (Node, Apache, Nginx, etc) that can serve the necessary JavaScript files to your browser will work. However, instructions for doing that are beyond the scope of this introduction.

In fact, you can run PCjs simulations without a web server at all, using the "file:" protocol instead of "http:". However, most of the machine configurations require additional resource files (ROMs, disk images, etc), which are included in the project, but unless all the resource files are moved into a single directory (as they are in these Demos), your browser will probably be unable to load all of them, due to security restrictions. Using the bundled web server is the preferred solution.

The project includes a large selection of disk images, and a powerful DiskDump utility that runs on both the client and server, featuring a command-line interface (CLI) and web server API. Originally created to dump existing disk images as JSON, DiskDump has evolved into a full-featured disk image generator, capable of creating PC-compatible diskette and hard disk images from either lists or directories of files (including all subdirectories).

Installing PCjs with Node

The following instructions were originally written for OS X. However, users of other operating systems should have no problem following along. There are some prerequisites:

  • Node with NPM (download an installation package for your OS from
  • Git (included with OS X Developer Tools; separate download required for Windows)

Some additional (optional) tools are also recommended:

  • Python (included with OS X; separate download required for Windows)
  • GitHub (useful for getting Git set up on Windows; also available for OS X)

Once you have the prerequisites, open a command-line window, cd to the directory where you'd like to install PCjs, and type the following commands:

git clone pcjs
cd pcjs
npm install --production
node server.js

Now open a web browser and go to http://localhost:8088/. You're done!

The current version of Node (0.10.32 at the time of this writing) should work fine, but version 0.10.26 is what's been used to develop and test PCjs so far.

Also, server.js was originally written using Express v3. Since then, Express v4 has been released, but the npm install command above will make sure that v3 is installed locally.

The plan is to eventually move development to a newer version of Node, and migrate the PCjs server to a newer version of Express; there's no desire to remain stuck in the past (well, ignoring the fact that PCjs is the quintessential "stuck in the past" project), but there's also no urgency to update.

Installing PCjs with Jekyll

PCjs can also be used with Jekyll and the Ruby WEBrick web server, now that a gh-pages branch has been created to work with GitHub Pages. This is how the project is currently set up at

This isn't going to be a Jekyll "How To" guide, because that would unnecessarily repeat all the information available at GitHub Pages. But we'll summarize the basic steps, which replace the npm and node steps above.

To install Jekyll for use with PCjs:

  1. Install Ruby (on OS X, it should already be installed)
  2. Install Bundler (on OS X, run sudo gem install bundler)
  3. Checkout the gh-pages branch, since only that branch contains all the Jekyll-related files
  4. Create a Gemfile containing gem 'github-pages' (this is already checked in)
  5. Run bundle install (GitHub Pages alternatively suggests: bundle exec jekyll build --safe)
  6. Run bundle exec jekyll serve to start the web server

Now open a web browser and go to http://localhost:4000/. You're done!

Some useful Jekyll server options include:

bundle exec jekyll serve --host= --config _config.yml,_developer.yml

The --host option makes it possible to access the web server from other devices on your local network; for example, you may want to run PCjs on your iPhone, iPad, or other wireless device. And by adding _developer.yml, you can override the Jekyll configuration defaults in _config.yml. Using development (non-production) settings in _developer.yml is analogous to running the Node web server with certain development options; see Debugging PCjs.

GitHub Pages says you can run jekyll serve instead of bundle exec jekyll serve, but with the addition of more gems to Gemfile (eg, jekyll-sitemap), running jekyll serve may trigger dependency errors on some systems. bundle exec jekyll serve should always work.

Don't see any YML files in the root of your project? You probably forgot to switch to the gh-pages branch:

git checkout gh-pages

Last but not least, run bundle update periodically to keep Jekyll up-to-date.

Building PCjs

Unlike a typical project, where you have to build or configure or make something, PCjs is "ready to run". That's because both the compiled and uncompiled versions of PCjs emulation modules are checked into the project, making deployment to a web server easy.

However, in order to build and test PCjs modifications, you'll want to use Grunt and the Grunt tasks defined by Gruntfile.js.

Although Grunt was installed locally when you ran npm install, you'll also want to install the command-line interface to Grunt. You can install that locally as well, but it's recommended you install it globally with -g; OS X users may also need to preface this command with sudo:

npm install grunt-cli -g

Now you can run grunt anywhere within the PCjs project to build an updated version. If no command-line arguments are specified, grunt runs the "default" task defined by the project's Gruntfile; that task runs Google's Closure Compiler if any of the target files (eg, pcx86.js or pcx86-dbg.js in the versions directory) are out-of date.

To ensure consistent compilation results, a copy of the Closure Compiler has been checked into the /bin folder. This version of Closure Compiler, in turn, requires Java v7 or later. Use the following commands to confirm that everything is working properly:

java -version

which should report a version >= 1.7; eg:

java version "1.7.0_67"
Java(TM) SE Runtime Environment (build 1.7.0_67-b01)
Java HotSpot(TM) 64-Bit Server VM (build 24.65-b04, mixed mode)

Then run:

java -jar bin/compiler.jar --version

which should report:

Closure Compiler (
Version: v20160911
Built on: 2016-09-13 16:51

If you don't have Java installed, it's recommended that you install the JDK (not the JRE), because the JRE may not update your command-line tools properly. Note that Java is used only by the Closure Compiler; none of the PCjs client or server components use Java.

Newer versions of the Closure Compiler should work as well, and at some point, a newer version will be checked into the project.

Building with Gulp (and the JavaScript-based Closure Compiler)

I've started dabbling with Gulp, but the current gulpfile has a long way to go before it can replace the Gruntfile. At the moment, all Gulp builds is a single emulation module with hard-coded settings, using Google's new JavaScript-based Closure Compiler.

Here's what I installed to get Gulp working:

sudo npm install -g gulp
npm install --save-dev gulp gulp-concat gulp-rename gulp-replace gulp-header gulp-foreach gulp-wrapper run-sequence
npm install --save-dev google-closure-compiler-js

Running gulp should build a new pcx86.js in the versions directory. However, you should consider Gulp support (and anything built with Gulp) as experimental until further notice. The JavaScript-based Closure Compiler is in a state of flux as well; for example, output_wrapper support is documented in their blog but hasn't been implemented yet.

Using PCjs

From The Browser

The PCjs Node web server is little more than a file/directory browser for the PCjs project, plus a collection of APIs.

If a URL corresponds to a PCjs project folder and no "index.html" exists in that folder, the Node web server loads an HTML template (common.html) and generates an "index.html" for that folder.

The contents of the "index.html" will vary depending on the contents of the folder; for example, if the folder contains a, then that Markdown file is converted to HTML and embedded in the "index.html". Similarly, if the folder contains a machine XML file, that is embedded as well.

To work well with both the Node and Jekyll web servers, all Markdown files containing one or more embedded machines should contain a Jekyll "Front Matter" header that describes the machines. For example, here's the header from the home page (

layout: page
permalink: /
  - type: pcx86
    id: ibm5150
    name: "IBM PC (Model 5150) with Monochrome Display"
    config: /devices/pcx86/machine/5150/mda/64kb/machine.xml
  - type: c1p
    id: demoC1P
    config: /devices/c1p/machine/8kb/large/machine.xml

Then the following lines are inserted at the points where the machines should appear:

{% include machine.html id="ibm5150" %}
{% include machine.html id="demoC1P" %}

For more information on all the machine options supported in a Markdown file, see the project's Jekyll include file machine-engines.html.

From The Command-Line

The PCx86 client app can also be run from the command-line mode using Node, making it possible to script the application, run a series of automated tests, etc:

cd modules/pcx86/bin
node pcx86

The pcx86 script in modules/pcx86/bin loads all the PCx86 browser scripts listed in the root package.json and then starts a Node REPL ("read-eval-print loop"). The REPL handles a few special commands (eg, "load", "quit") and passes anything else to the PCx86 Debugger component. If no Debugger component has been created yet, or if the Debugger didn't recognize the command, then it's passed on to eval(), like a good little REPL.

Use the "load" command to load a JSON machine configuration file. A sample ibm5150.json is provided in the bin directory, which is a "JSON-ified" version of the machine.xml displayed on the home page.

The command-line loader creates all the JSON-defined machine components in the same order that the browser creates XML-defined components. You can also issue the "load" command directly from the command-line:

node pcx86 --cmd="load ibm5150.json"

In fact, any number of "--cmd" arguments can be included on the command-line. A batch file syntax will eventually be added, too.

When a PCjs machine runs in a browser, an XML machine configuration file is transformed into HTML with a set of DIVs for each component: an "object" DIV whose data-value attribute provides the initialization parameters for the corresponding component, along with a set of optional "control" DIVs that the component can bind to (eg, a Run button, or a visual representation of DIP switches, or whatever).

When a PCjs machine is run from the command-line, there is no XML, HTML, or DIVs involved; this is basically a "headless" version of the machine, so there is no simple way to view its video display or interact with its keyboard, mouse, etc. You have to use Debugger commands to dump the machine's video buffer.

Since I was not inclined to add XML support to my Node environment, this has created some divergence between client and server operation: PCjs machines on the client supports only XML machine configuration files, whereas PCjs machines on the server supports only JSON machine configuration files.

I haven't decided whether I'll add support for JSON configuration files to the client, or add some XML-to-JSON conversion to the server, or both.

Debugging PCjs

NOTE: The following information assumes you're running Node as your local web server, not Jekyll. You can certainly debug PCjs while running Jekyll (ideally with --config _config.yml,_developer.yml), using http://localhost:4000/ and your favorite web browser's Developer Tools, but none of the special server or client features discussed below will be available.

Server Components

To help test/debug changes to PCjs server components (eg, DiskDump, HTMLOut), you can start the server with some additional options; eg:

node server.js --logging --console --debug

The --logging option will create a node.log that records all the HTTP requests, --debug will generate additional debug-only messages (which will also be logged if --logging is enabled), and --console will replicate any messages to your console as well.

If you want server.js to use a different port (the default is 8088), set PORT in your environment before starting the server:

export PORT=80

or add --port to your command-line:

node server.js --logging --console --debug --port=80

A complete list of command-line options can be found in server.js.

Client Components

A special command parameter ("gort") can be appended to the URL to request uncompiled client source files, making the PCjs emulators much easier to debug, albeit much slower:


The "gort=debug" command is unnecessary if the server is started with --debug; the server always serves uncompiled files when running in debug mode.

Conversely, if the server is in debug mode but you want to test a compiled version of PCx86, use:


and the server will serve compiled JavaScript files, regardless whether the server is running in debug mode or release mode.

Another useful gort command is "gort=nodebug", which is like "gort=debug" in that it serves uncompiled files, but it also sets the client-side DEBUG variable to false, disabling all debug-only runtime checks in the client and allowing the simulation to run much faster (although not as fast as compiled code):


Regrettably, the gort command "Klaatu barada nikto" is not yet recognized. Fortunately, there are no (known) situations where PCjs could run amok and destroy the planet.

Other parameters that can be passed via the URL:

  • autostart: set it to "true" to allow all machines to start normally, "false" to prevent all machines from starting, or "no" to prevent all machines from starting unless they have no Run button; e.g.:


  • aspect: set it to a numeric value >= 0.3 and <= 3.33 to modify the default aspect ratio of a machine's screen on the specified page; e.g.:


Updating PCjs


To start developing features for a new version of PCjs, here are the recommended steps:

  1. Change the version number in the root package.json (and _config.yml)
  2. Run the "grunt promote" task to bump the version in all the machine XML files
  3. Make changes
  4. Run "grunt" to build new versions of the apps (eg, "/versions/pcx86/1.x.x/pcx86.js")

You might also want to check out the blog post on PCjs Coding Conventions.

You may also want to skip step #2 until you're ready to start testing the new version. Depending on the nature of your changes, it may be better to manually edit the version number in only a few machine XML files for testing, leaving the rest of the XML files pointing to the previous version. Run "grunt promote" when the new version is much closer to being released.


In the course of testing PCjs, there may be stale "index.html" files that prevent you from seeing application updates, changes to files, etc. So before running Node, you may want to "touch" the default HTML template:

touch modules/shared/templates/common.html

The HTMLOut module compares the timestamp of that template file to the timestamp of any "index.html" and will regenerate the latter if it's out-of-date.

There's a TODO to expand that check to include the timestamp of any local file, but there are many other factors that can contribute to stale "index.html" files, so usually the safest thing to do is "touch" the common.html template, or delete all existing "index.html" files, either manually or with the Grunt "clean" task:

grunt clean


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 © 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

Learn more about the PCjs Project and PCx86. To create your own PCx86 machines, see the PCx86 Documentation for details.

If you have questions or run into any problems, feel free to tweet or email.