Real differences between "java -server" and "java -client"?

Oracle’s online documentation provides some information for Java SE 7.

On the java – the Java application launcher page for Windows, the -client option is ignored in a 64-bit JDK:

Select the Java HotSpot Client VM. A 64-bit capable jdk currently ignores this option and instead uses the Java HotSpot Server VM.

However (to make things interesting), under -server it states:

Select the Java HotSpot Server VM. On a 64-bit capable jdk only the Java HotSpot Server VM is supported so the -server option is implicit. This is subject to change in a future release.

The Server-Class Machine Detection page gives information on which VM is selected by OS and architecture.

I don’t know how much of this applies to JDK 6.

IIRC, it involves garbage collection strategies. The theory is that a client and server will be different in terms of short-lived objects, which is important for modern GC algorithms.

Here is a link on server mode. Alas, they don't mention client mode.

Here is a very thorough link on GC in general; this is a more basic article. Not sure if either address -server vs -client but this is relevant material.

At No Fluff Just Stuff, both Ken Sipe and Glenn Vandenburg do great talks on this kind of thing.