Differences between JVM implementations

Question

Where do JVM Implementations differ (except licensing)? Does every JVM implement Type Erasure for the Generic handling?

Where are the differences between:

Answer 1

If the JVM claims to be Java it must pass the TCK, providing a lot of stock funcitonaltiy.

The differences are in non-core places, like garbage collection, the jconsole/visualvm in the Sun JVM, precompilation etc.

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clarification: TCK is the test suite that a virtual machine has to pass in order to be officially Java compliant.

Answer 2

Another difference between JVMs is behaviour on undocumented API. (e.g. com.sun.xxx) For example, Sun's JVM and IBM's JVM both have slightly different behaviour on signal handling. (IBM's JVM doesn't allow the application to trap the "INT" signal in certain cases.)