Java is known to be a valuable technology for building platform independent applications, based on an independent execution environment provided by a virtual machine (JVM, Java Virtual Machine) and an API formed by a set of classes. The Java platform was conceived as a solution for application transportation between heterogeneous platforms without the need of adapting and recompiling the source code. Some previous analyses of Sun JVM implementation (Java 2 SDK 1.2.2-006) establish that the HPI (Host Porting Interface) layer does not abstract enough the concurrency offered by the underlying platform.Consequently, the execution of the same Java application over distinct HPI platform implementations offers different behavior, being a possible cause of incorrect program execution. We consider that it's necessary a new HPI layer that can really abstract the concurrency supplied by the platform, giving a set of operations whose semantic does not vary between diverse platform implementations. With the new HPI, the JVM will be capable to perform a uniform behavior independently of the operating system. The new JVM with ULT offers an acceptable performance on multiprocessor architectures increasing the throughput and it implements a synchronization mechanism that achieves better results than the original JVM on SMP architectures.