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Borrowing a page from the mainframe world, and operating systems like IBM's VM, virtual servers are becoming increasingly popular as a way to control costs and space needs as well as increase both manageability and flexibility.
So what is it?
It's software, run either as its own operating system or under another (Windows, Linux, etc) that creates a "virtual" environment. It carves out some disk space, an allowed amount of memory, emulates a network interface card, etc. and that is presented as a computer. If you're using the management tools, you see boot up screens, BIOS settings, etc. - just as if it was a real server. In reality, the virtualization software is sharing the host computer's CPU, RAM, etc. between all of the virtual servers running on it. A guest operating system running on virtual hardware are unaware of both the nature of the "hardware" it is running on and other guest / virtual servers running on the same host server.
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