The end result is achieved through using server virtualisation technology, which allows one physical platform to run multiple virtual machines simultaneously.
Each virtual machine has its own processor(s), memory, disks and network interfaces, and the operating system running in each virtual machine is referred to as a ‘guest’. Functionally, each virtual machine is autonomous and unaware that the hardware is being shared, enabling multiple servers (even of different operating systems or versions) to run on just one hardware platform.
This means, for example, that a single machine is able to support three different virtual machines such as:
•Windows Server 2003 and Exchange Server 2003
•Windows Server 2000 and SQL 2000
•A domain controller (DC)
The third machine in the example above, a virtualised DC, is particularly popular with large distributed branch offices that require a local DC but do not wish to pay for the physical asset. It is also useful for disaster recovery sites for the same reason. The key to these solutions is in the complete autonomy between virtual machines and their respective operating systems and applications.