A Java Virtual Machine is a set of computer software and data structures that use a virtual machine model to execute other computer programs and scripts. JVM model use a form of computer intermediate language commonly referred to as Java bytecode
To run the java applets, some websites as well as some programs require Java runtime Machine to perform.
*If same is not installed on your PC, you can download and install on below link:
Under the above mentioned websites, there are JRM for almost all operating systems.
See also http://www.microsoft.com/java/default.mspx
on Java support by Microsoft.
Sun has signed an agreement with Java to support its Java Virtual Machine but however did not develop and distribute more which however enables anyone to install and use the Java Virtual Machine.