Microsoft Virtual Server is a virtualization solution that facilitates the creation of virtual machines on the Windows XP, Windows Vista and Windows Server 2003 operating systems. Originally developed by Connectix, it was acquired by Microsoft prior to release. Virtual PC is Microsoft's related desktop virtualization software package.
Virtual machines are created and managed through an IIS web-based interface or through a Windows client application tool called VMRCplus.
The current version is Microsoft Virtual Server 2005 R2 SP1. New features in R2 SP1 include Linux guest operating system support, Virtual Disk Precompactor, SMP (but not for the Guest OS), x86-64 (x64) Host OS support (but not Guest OS support), the ability to mount virtual hard drives on the host OS and additional operating systems including Windows Vista. It also provides a Volume Shadow Copy writer which enables live backups of the Guest OS on a Windows Server 2003 or Windows Server 2008 Host. A utility to mount VHD images is also included since SP1. Virtual Machine Additions for Linux are downloadable here. Officially supported Linux guest operating systems include Red Hat Enterprise Linux versions 2.1-5.0, Red Hat Linux 9.0, SUSE Linux and SUSE Linux Enterprise Server versions 9 and 10.[1]

Learn more about Microsoft® Hyper-V Server 2008 R2 today. The next generation of Virtual Server is here; Microsoft® Hyper-V™ Server 2008 R2 is a FREE stand-alone product that provides a reliable and optimized virtualization solution enabling organizations to improve server utilization and reduce costs.
Get the Overview
The most cost-effective server virtualization technology is now available as a free download. Discover Virtual Server 2005 R2, a key component of any server consolidation strategy. Increase hardware utilization and cut power costs while enabling your organization to rapidly configure and deploy new servers.
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Upgrade to Service Pack 1
Now available Virtual Server 2005 R2 SP1. The latest release leverages hardware-assisted technology and enhanced support. Get upgraded today.
Explore Computing Options
Explore the new flexible desktop computing options that are available with Windows Vista Enterprise Diskless PCs and Windows Vista.
Update for Virtual Server 2005 R2 SP1 Available
This update qualifies support for the following additional Guest and Host Operating Systems: Windows Vista SP1 (Business, Enterprise, Ultimate), Windows XP SP3, Windows Server 2008 (Standard, Enterprise, Datacenter, Web).
Evaluate VHDs
Discover the VHD Test Drive Program. Take a spin through the enhanced server-based evaluation software and VHD catalog available from Microsoft.
Manage Virtualization
SCVMM provides centralized administration of Virtual Server, enables increased physical server utilization and rapid provisioning of new virtual machines.