Virtual machine is a collection of software like JVM (java virtual m/c) that provides run time environment (e.g. data structure support) to user applications. Such software is now referred with the terms virtualization that is running two or more copies of the same operating system or two or more different operating systems and virtual servers. The host software, which provides this capability, is often referred to as a virtual machine monitor or hypervisor. It resides between the hardware and the "guest" operating systems.
There are four major conceptual models of Virtual Machines used today and cater for different problem The IBM Model as demonstrated in the IBM S/390 solved the need for a single computer system that could simulate multiple computers with different operating systems.
instruction set and maps JVM calls to operating system calls. It simulates a fake CPU that interprets the fake CPU instructions (what is usually referred to as byte code). The most significant feature of the Java Virtual Machine the ability write a program once and execute it with Java Virtual Machines on multiple platforms. The OSI Virtual Machine and the Unix Virtual Machine, represented by the Unix user shell are used to create operating systems and providing services and functions at the operating system level that did not exist in the system hardware.
The OSI Virtual Machine model solved the problem of providing services and functions at ...