What is the difference between a JVM v1.5 and v5.0

None. Sun just decided to change the notation. Versions 1.5 and 5.0 are exactly the same.

Before v1.5, the versions were noted 1.1, 1.2, 1.3, etc. This lead to some confusion because there were big changes made from 1.1 to 1.2, from 1.3 to 1.4 and from 1.4 to 1.5. This was not properly reflected in the version numbers. Sun Microsystems (which sets the Java Language Specifications) finally decided to remedy to this with version 1.5 that it properly renamed 5.0. This should have been done a long time ago, IMHO. Unfortunately, there is still some confusion because Sun Microsystems kept the 1.5 notation is some places. I will be using the 1.5 notation mainly because it is the one that will be returned by the

java -version

command used to determine the version number of the JVM installed on a system.