Server virtualization takes advantage of idle resources to reduce the number of servers required to provide services to users.
A special program called the hypervisor is used to manage the computer resources and various VMs. It provides VMs access to all of the hardware of the physical machine such as CPUs, memory, disk controllers, and NICs. Each of these VMs runs a complete and separate operating system.
With virtualization, enterprises can now consolidate the number of servers. For example, it is not uncommon for 100 physical servers to be consolidated as virtual machines on top of 10 physical servers using hypervisors. In the figure, the previous eight dedicated servers have been consolidated into two servers using hypervisors to support multiple virtual instances of the operating systems.
The figure displays the hypervisor structure on two servers. The hardware component is at the lowest level with the hypervisor on top of the hardware. Connected to the hypervisor are four instances of the operating system. For server 1 there are four instances of the Windows OS. On server 1, above the four instances of the Windows OS are services for Web Server, Email Server, SQL server and File server. For server 2 there are two instances of the Windows OS and two instances of a Linux OS. On server 2, above the two instances of the Windows OS are services for DHCP server and AD server. On server 2, above the two instances of the Linux OS are services Radius server and NMS server.
Many organizations use server virtualization to optimize network resources and reduce equipment and maintenance costs. Organizations are also using client-side virtualization to enable users with specific needs to run VMs on their local computer.
Client-side virtualization is beneficial for IT staff, IT support people, software developers and testers, and for educational reasons. It provides users with resources to test new operating systems, software, or to run older software. It can also be used to sandbox and create a secure isolated environment to open or run a suspicious file.
Some terms that are used when discussing client-side virtualization include:
- Host computer – This is the physical computer controlled by a user. VMs use the system resources of the host machine to boot and run an OS.
- Host operating system (host OS) – This is the operating system of the host computer. Users can use a virtualization emulator such as VirtualBox on the host OS to create and manage VMs.
- Guest operating system (guest OS) – This is the operating system that is running in the VM. Drivers are required to run the different OS version.
The guest OS is independent of the host OS. For example, the host OS could be Windows 10 and the VM could have Windows 7 installed. This guest of the VM would be Windows 7. In this example, the guest OS (Windows 7) does not interfere with the host OS (Windows 10) on the host computer.
Host and guest operating systems do not need to be of the same family. For example, the host OS could be Windows 10, while the guest OS is Linux. This is of benefit for users that need to increase the functionality of their host computer by running multiple operating systems at the same time.
The figure displays a logical virtual machine diagram. The bottom gray box represents the physical computer with its host OS (e.g., Windows 10). Hyper-V, Virtual PC, and VirtualBox are examples of virtualization software or emulator that could be used to create and manage the three VMs shown in the top of the figure.
The figure on this page is a diagram that represents a logical virtual machine. Three boxes aligned horizontally are each labeled as, ‘Virtual Machine’. Each of the virtual machines contains two smaller boxes stacked vertically and labeled as, ‘Applications on Guest OS’ and ‘Guest OS’. Below the three virtual machines is a larger box the width of the three virtual machines. This box is labeled as, ‘Physical Machine’. The physical machine contains two smaller boxes, also the width of the three virtual machines, stacked vertically and labeled as, ‘Virtualization Software (Hyper-V, Virtual PC, VirtualBox, etc.)’ and ‘Host OS’. Below this is a label of physical machine.