Unless provided explicitly, Java VM will set up several performance-related options depending on current environment. This mechanism is called ergonomics. You can see what defaults would be used on the machine by invoking:
The decision on the settings will be made based on the number of processors and total memory installed in the system. On my 32bit EeePC with 2 processors (as visible by OS) and 2GB memory, the output is:
And just for comparison, the output from Oracle Java 7:
On 64bit system with 8 CPUs and 16GB memory, the output is:
Oracle Java 7 again gives exactly the same ergonomics defaults.