Last month I talked about virtual machines and virtualization in general. This month I am going to go into more detail about the hypervisor. A hypervisor is the core of a server virtualization solution. A hypervisor is a very small program or operating system that runs on your server and allows your server to run multiple virtual servers at the same time.
Once the hypervisor is installed on your server, you can begin building and running virtual servers. As each virtual server is turned on, the hypervisor provides a set of resources to each virtual server based on the settings the virtual server was created with — a digital mirage of sorts, telling the virtual server you have X amount of memory and X amount of hard drive space. Once a virtual server is turned on, the hypervisor continues to monitor the virtual server and can be configured to make sure all of its needs are met by the physical hardware, allocating the needed amount of physical resources to the virtual server as they are needed and releasing them when no longer in use.
The hypervisor can be controlled remotely using management software designed to make monitoring, moving, and backing up virtual machines easy and intuitive. This management software can tell the hypervisor to pause or shut down a machine. It can tell the hypervisor to begin moving a virtual machine from one server to another or to begin backing up.
VMware, Microsoft, and Citrix all have hypervisors capable of running virtual Windows servers, as well as Linux and other server operating systems. Each hypervisor provides the same basic functionality, allowing you to create virtual servers and run them. What you might not know is that free versions of these hypervisors are available to download. Your company could begin virtualizing its servers today for free. It is important to mention that Microsoft has a number of licensing requirements that should be followed when virtualizing their operating systems. These licensing requirements are different for each edition of the operating system. Before you put any virtual Windows Servers into production, make sure you are in compliance with the license requirements.