Java Virtual Machine

In computing, a program that sits on top of a computer's usual operating system and runs Java applets.

Different computers require different JVMs but they should run the same Java code. This means that servers only need to provide one version of each applet, instead of different ‘native code’ versions for PCs, Apple Macintoshes, and Unix workstations, as is the case with other plug-ins.

A JVM is commonly supplied as part of a Web browser but may be included as part of the operating system.

Because the JVM interprets Java code – applets are not compiled into processor-specific machine code like normal programs – Java tends to be slow. However, a just-in-time compiler (JIT) can be used to compile code on the fly for faster results. Another problem is that not all JVMs are the same, and incompatibilities mean applets may not in fact run correctly on every machine, as intended.