J2SE 5.0 Server Ergonomics is not on by default on Windows. The basic reasoning here is that Windows is largely a client platform and automatic server tuning may negatively impact startup performance. We are revisiting this for Mustang, but for now do the following to enable server ergonomics on Windows: 1). Specify JVM tuning options equivalent to server ergonomics java -server -Xmx1g -XX:+UseParallelGC 2). Check to make sure server ergonomics is enabled by checking the JVM version: $ java -server -Xmx1g -XX:+UseParallelGC -version java version "1.6.0-rc" Java(TM) 2 Runtime Environment, Standard Edition (build 1.6.0-rc-b69) Java HotSpot(TM) Server VM (build 1.6.0-rc-b69, mixed mode) If you see "Server VM", you're ready to test.