 <p>Read <a href="http://docs.oracle.com/javase/7/docs/technotes/guides/vm/performance-enhancements-7.html">here</a></p> <blockquote> <p>Tiered Compilation</p> <p>Tiered compilation, introduced in Java SE 7, brings client startup speeds to the server VM. Normally, a server VM uses the interpreter to collect profiling information about methods that is fed into the compiler. In the tiered scheme, in addition to the interpreter, the client compiler is used to generate compiled versions of methods that collect profiling information about themselves. Since the compiled code is substantially faster than the interpreter, the program executes with greater performance during the profiling phase. In many cases, a startup that is even faster than with the client VM can be achieved because the final code produced by the server compiler may be already available during the early stages of application initialization. The tiered scheme can also achieve better peak performance than a regular server VM because the faster profiling phase allows a longer period of profiling, which may yield better optimization.</p> </blockquote>