Virtual Machines

2.8 Virtual Machines
The concept of a virtual machine is to provide an interface that looks like independent hardware, to multiple different OSes running simultaneously on the same physical hardware. Each OS believes that it has access to and control over its own CPU, RAM, I/O devices, hard drives, et

2.8.3 Simulation
An alternative to creating an entire virtual machine is to simply run an emulator, which allows a program written for one OS to run on a different OS.
For example, a UNIX machine may run a DOS emulator in order to run DOS programs, or vice-versa.

2.8.4 Para-virtualization
Para-virtualization is another variation on the theme, in which an environment is provided for the guest program that is similar to its native OS, without trying to completely mimic it
Solaris 10 uses a zone system, in which the low-level hardware is not virtualized, but the OS and its devices ( device drivers ) are.

2.8.6 Examples
2.8.6.1 VMware
2.8.6.2 The Java Virtual Machine



http://www.cs.uic.edu/~jbell/CourseNotes/OperatingSystems/2_Structures.html