This chapter briefly covered virtualization and hypervisors to provide a background for understanding the JRockit Virtual Edition product family. Virtualization is the practice of running software on emulated, virtualized, hardware, and may potentially increase the resource utilization of a machine park. Virtualization also typically comes with some overhead because of the hardware emulation. A virtualized piece of software, for example an operating system, is called a guest. The two most important types of virtualization are full virtualization, where the guest does not know it is virtualized and can run unmodified in the virtualized environment, and paravirtualization that requires the guest to use a communication layer with the underlying system.
The piece of code making it possible to run multiple guests on a single piece of hardware is called a hypervisor. Except for "faking" the hardware to the guest and handling context switching between guests, it can help provide services like device drivers. Hypervisors are either hosted, running as standard operating system applications, or native, installed on bare metal hardware.
JRockit Virtual Edition works by removing the need for a standard general purpose operating system layer in a virtual application stack. Thereby, it increases the performance of a virtualized system. JRockit Virtual Edition can be likened to an operating system that is only able to run a single process—the JVM. Having to provide only the functionality the JVM needs, JRockit VE is vastly simpler than any general purpose operating system. This provides both speed and security.
Offline manageability of virtualized software running on top of JRockit VE is handled by the Image Tool that is part of the JRockit VE product suite. Online manageability and deployment is handled by a hypervisor-specific management framework, such as Oracle VM Manager.
Finally, this chapter discussed how to potentially gain even more power and performance in virtualized Java environments, given the prerequisite that we completely control everything between the hypervisor and the Java application. Our longterm goal is to provide virtual environments for Java that actually perform better than physical ones. We believe this can be done.