Virtual Computers
Posted on June 24, 2006
Filed Under Software, Windows |
It can be very useful to run different operating systems on a network or even a single computer. Linux for example might offer software or services that Windows doesn’t and for testing purposes, an operating system that can be easily deleted and recreated if something goes wrong is invaluable.
Running different operating systems used to mean either purchasing more than one computer, or dual-booting a single computer. Multiple computers were of course an expensive option and dual-booting allowed only one operating system to run at a time. Dual-booting also means messing with the way the computer boots and that can potentially be dangerous.
That’s all changing thanks to virtualization.
The term “virtual” in the computing world refers to something that is not real. A virtual computer is one that runs entirely in software and does not physically exist. Virtualization software allows an operating system to be installed in software rather than in a real computer.
Virtualization software is installed on a “host” system and can then provide as many virtual computers as the host’s resources permit. VMWare for example runs on either Windows or Linux (the host system) and uses some of the resources available to the host (disk space, memory, etc) to allocate to virtual machines.
If there is 512 MB of memory and 10 GB of hard drive space available on a Windows machine for example, you could allocate 256 MB of memory and 4 GB of hard drive space to a Linux virtual machine.
The Linux virtual machine in this case runs entirely in software. It looks and acts exactly like a real and separate Linux computer but requires only a host computer and the virtualization software to run in. In other words it is not tied to the computer hardware and can easily be transferred from physical machine to physical machine.
Most virtualization software works by creating a file or series of files on the host system that contain the virtual machine. The files can be moved easily or completely deleted if the virtual machine is no longer needed.
The major benefits of this approach are that both the host and virtual machines run at the same time and the virtual machine is completely isolated from the physical hardware. A virtual machine can be moved to another physical computer in minutes and this has major implications when it comes to quickly recovering from a disaster.
On a workstation, virtualization software shines at providing a safe and effective testing platform. Testing new software for example can be done in a virtual machine without the risk of harming the host operating system.
On a server the picture gets more interesting. One could buy a fully loaded server and run more than one server operating system on it. Windows and Linux can run at the same time, SQL and Exchange server can be separated without the need for additional hardware, or a single server could be virtualized solely to allow for easy recovery in the event of disaster.
In our next column we’ll look at virtualization software and some of the scenarios that make virtual machines an attractive alternative to physical computers and servers.
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