Are virtual machines hardware or software dependents?

A virtual machine allows multiple operating systems to co-exist on the same hardware at the same time. You can switch to each without losing your place in the other OS.

This is not the same as multiple boot.

The penalty is that the OS's run slower.

The OS must be able to natively run on the hardware in the strict definition.

In a non-strict definition the Macintosh emulated the 68000 processor on a PowerPC platform. They also had a program that would run Windows in the PowerPC platform, but the makers had access to the Windows source code.

Do a Google search on Microsoft Virtual Server and also VMWare Virtual Server. Both will return the two most used virtual computer platform providers.

VMWare has been doing it the longest. We are currently over 90% virtualized in our environment and are running VMWare ESX with clustered host servers connected to a Storage Area Network (SAN). They allow you to run many different "computers" on a small grouping of hardware.

For example, on four physical hosts, we are running almost 30 servers. They all share the same hardware and the hosts will allocate the resources based on need.