Java Virtual Machine
JVM: Java Virtual Machine
The JVM was rather revolutionary in the world of computers in that Sun Microsystems (the creators of the various Java technologies) pushed Java out the door very effectively. The use of a Virtual Machine to run bytecode had been played with before but it was Sun who pushed the technology with a language that both new programmers and die hard C programmers could both get to grips with.
However, Sun's greatest move was utilising the JVM to allow Java programs to run wherever there was a JVM. This allowed the hard work of writing portable code to be mostly forgotten as the low level interaction with the computer was taken care of by the JVM. Windows, buttons, writing to disk, talking to the Operating System all was handled by standard routines which the JVM processed and translated into the specific instructions of the host machine.
Needless to say most people will have a JVM present on their system since it is necessary to run any Java programs but one doesn't have to use the one made by Sun. IBM created a clone, as well as Microsoft and there is even an Open Source version. However, none work quite as well as Sun's incarnation nor come with quite the support.