More about the legalities of running multiple virtual machines on the desktop:I did some research on Microsoft's website. The language seems quite clear: OS licenses are tied to physical machines, not virtual machines.In the current EULA for Windows XP Professional Edition Service Pack 2, the relevant text says:1.1 Installation and use. You may install, use, access, display and run one copy of the Software on a More about the legalities of running multiple virtual machines on the desktop:I did some research on Microsoft’s website. The language seems quite clear: OS licenses are tied to physical machines, not virtual machines.In the current EULA for Windows XP Professional Edition Service Pack 2, the relevant text says: 1.1 Installation and use. You may install, use, access, display and run one copy of the Software on a single computer, such as a workstation, terminal or other device (“Workstation Computer”). The Software may not be used by more than two (2) processors at any one time on any single Workstation Computer.Seems clear to me that the license is tied to the hardware, not to any VM running on the hardware.Here’s the relevant text from “MICROSOFT SOFTWARE LICENSE TERMS WINDOWS VISTA BUSINESS“:2. INSTALLATION AND USE RIGHTS. Before you use the software under a license, you must assign that license to one device (physical hardware system). That device is the “licensed device.” A hardware partition or blade is considered to be a separate device. a. Licensed Device. You may install one copy of the software on the licensed device.You may use the software on up to two processors on that device at one time. Except as provided in the Storage and Network Use sections below, you may not use the software on any other device.And, f. Use with Virtualization Technologies. You may use the software installed on the licensed device within a virtual (or otherwise emulated) hardware system. If you do so, you may not play or access content or use applications protected by any Microsoft digital, information or enterprise rights management technology or other Microsoft rights management services or use BitLocker. We advise against playing or accessing content or using applications protected by other digital, information or enterprise rights management technology or other rights management services or using full volume disk drive encryption.This last is a baffling set of restrictions, but does not require a separate license for each VM.Note that there is a lot of confusion on this subject, driven by the use of “Virtualization” both for server-side processing (for example Citrix, where you do need a license for each user) and for multiple VMs on the desktop (what I’ve been talking about).– Bob Technology Industry