Platform Specific Information: Finding a Good JVM

Jython is 100% Pure Java and should run successfully on any bug-free fully 1.1 or 1.2 compliant JVM. Unfortunately, such a beast can sometimes be hard to find. The following is a collection of notes for getting Jython to run (and run well) on specific OS's and JVM's. Since performance can also vary considerably across JVM implementations, this page will also contain information regarding Jython's performance on different platforms.

This list of platform specific information is clearly incomplete. If you find this information to be incorrect for your particular platform, or if you have tips for running Jython on a platform not mentioned on this page, please send that information to jython-dev. If your platform is not included in the list below, you might be able to get useful information from SUN's list of third-party JVM's.

Operating Systems


Java Development Environment 3.1.1 from SGI

Jython will work with the 3.0.1 version of the JDE (which is based on the 1.1.3 JVM), but there are a number of significant known bugs in this release. I strongly recommend using to the 3.1 release on this platform.


Following blackdown versions have been used with jython.
  • 1.3.0 ppc, i386
  • 1.2.2 i386, ppc
  • 1.1.8 v3 ppc, i386


Tower Technology Corporation

The TowerJ VM have shown impressive performance figures for some Jython application. TowerJ is still a not a complete java environment, but for some server type applications it can make performance around 2.6 times faster than the IBM and Blackdown JVM's. TowerJ is a commercial product that also runs on WinNT, Irix, HP, Solaris and others.


A guide for installation on Macintosh is available here

Mizutori Tetsuya has made available an application called JPython Runner to make it easier to use JPython on this system. More details on this system can be found at JPython Runner for Macintosh. This link also contains pointers to the latest JVM for Macintosh.

Hopefully, future releases of Jython will be able to incorporate either this technology or something like it to make life easier for Macintosh users.



  • Sun jdk 1.1.8
  • Sun jdk 1.2

Windows NT, 95, and 98, Windows 2000

JDK/JRE 1.3 from SUN (My recommendation for this platform)

This is amoung the fastest of the JVM's for Windows, and it also the most compatible with the official Java specification. I'd strongly encourage people to start with this VM, and only consider trying alternatives if they find performance to be a serious problem for their application.

JView from Microsoft

If you have IE 4.0 installed, you almost certainly already have this VM. Type "jview" at a command prompt to be sure. Note: if the copyright dates you see when you type "jview" do not include 1998, you have an older VM. Either download a recent version of IE 4.0, or download the VM directly from the site above.

If you want to write Jython code that takes advantage of Windows specific functionality (using win32 api's, interacting with COM objects, ...) then this VM will give you all of the platform specific functionality you could desire.

Cross-Platform JVM's


Jython does not work with the current version available from transvirtual. This appears to be both due to some small incompatibilities between this Java VM and SUN's version, as well as at least one serious issue which is the lack of a java.math.BigInteger class -- this lack will be a problem for any VM that only implements the PersonalJava subset of the full Java spec. It should be possible to get Jython working on this VM if someone has the time to invest, please let us know if you have any success here or need any help.