Virtual machines in Virtual Server

Virtual machines

Virtual Server 2005 can accommodate a large number of virtual machines on one physical computer. Virtual Server can support up to a maximum of 64 virtual machines. The practical limit of how many virtual machines you can run simultaneously depends on system resources, the amount of memory assigned to each virtual machine, and the total memory available on the physical computer. Virtual Server supports up to 3.6 gigabytes (GB) of RAM per virtual machine. Each virtual machine has a unique set of files for storing configuration information, an operating system, and data. This topic describes the virtual machine files and folders, CPU usage, and memory usage.

For more information about the components of Virtual Server, see Virtual Server Components.

Files and folders

Each virtual machine uses the following files:

  • A virtual machine configuration (.vmc) file in XML format that contains the virtual machine configuration information, including all settings for the virtual machine.
  • One or more virtual hard disk (.vhd) files to store the guest operating system, applications, and data for the virtual machine. For more information, see Virtual hard disks.

In addition, a virtual machine may also use one or more of the following files:

  • Any undo disk (.vud) files created by Virtual Server if the Undo Disks feature is enabled on the virtual machine.
  • One or more differencing disk (.vhd) files, if differencing disks have been created for any of the virtual hard disks assigned to the virtual machine.
  • A saved-state (.vsv) file, if the machine has been placed into a saved state.

By default, Virtual Server stores all the files that make up a virtual machine in one folder for simple management and portability. Virtual Server stores the files in a folder it creates with the same name as the virtual machine. If, for example, the virtual machine is named Windows 2000 Test, the folder is named Windows 2000 Test. By default, these folders are located in the Shared Virtual Machines folder, which is located in Documents and Settings\All Users\Documents\Shared Virtual Machines.

Renaming a virtual machine does not rename the virtual machine folder.

CPU usage

Each virtual machine runs on a separate thread in Virtual Server. This means that on a multiprocessor physical computer, more processors are available for use by the virtual machines. Each virtual machine uses a maximum of one processor; however, it may share the processor it is using with other virtual machines, depending on the number of processors on the physical computer and the number of running virtual machines.

Memory usage

Each virtual machine requires enough memory to run the operating system and applications, plus approximately 32 MB required for the emulated video RAM and code cache. You specify an amount of memory for the virtual machine when you create the virtual machine. The amount you specify represents the maximum amount of memory that the virtual machine can consume. You can modify this memory allocation only when the virtual machine is turned off. The virtual machine consumes memory only when it is running or paused. A virtual machine will not start if there is not sufficient memory available when you try to start it. If the virtual machine does not start, an error is logged to the Virtual Server event log.

The memory assigned for the virtual machine’s memory is allocated at a low level and is charged to the Virtual Server service. Because memory allocated by such a method is not charged to a process, the memory quoted by Task Manager in the host operating system for the Virtual Server service is not accurate. You can use Task Manager in the guest operating system to determine the current memory usage for a particular virtual machine.

Memory allocated to virtual machines is not available for paging by the host operating system.