Just-In-Time (JIT) compiler is valuable Java related technology that dynamically compiles selected bytecode methods of executing Java applications into native (binary code) methods, thus greatly reducing the overall execution time of such applications. IBM's JIT compilers provided with various configurations of J9VM are all based on the same advanced technology adapted for effective use with Java ME CLDC, Java ME CDC, Java SE, and Java EE configurations of J9VM. Specifically, the "embedded" JIT compiler used in Apogee's JREs does not implement, due to limited memory and CPU resources of targeted devices, the same set of optimizations that are implemented in the "desktop" JIT compiler, and does not include certain non-essential features that tend to increase the runtime footprint. However, this embedded JIT still implements all of the "high payoff" optimizations, which means that it typically achieves the 5 to 8 times runtime speed-ups of compiled Java applications compared with interpretive execution of such applications, while having the minimum overhead and small runtime footprint.
IBM JIT compiler technology is highly configurable and tunable for achieving the highest possible speed-ups of Java applications when subjected to JIT compilation. Specifically, it allows: