The average server in the average data center--it turns out--isn't doing much. Kind of like the salespeople at your average mall...but that would be another rant.
In order to increase reliability, we once proliferated servers. We balanced load by creating more servers and directing part of the work to one and part to others. Now IT departments are putting servers back together--sort of.
These virtual server (and virtual desktop) systems allow technologists to create multiple "virtual" servers on the same box. Now you can have a web server, a database server, an email server, and a file server all on one box, but each running in its own space and each with only the programs loaded that it needs.
Since these servers are often stored in data files, load balancing and disaster recovery also become easier. To move a load to another server, just copy the virtual machine file to the new system and start it up. Since virtual machines use the hardware interface of the underlying operating system (usually a simple installation of Windows Server or equivalent), moving a server isn't a hardware issue. And disaster recovery becomes easier since the virtual machine can be backed up intact and moved from one system to another at will.
You could even run Windows and Linux on the same server at the same time.
This trend is one to watch. It can save you money and make your computing more disaster-proof at the same time.
Virtualization Picks Up Steam - VARBusiness