Number of virtual processors in Hyper-V Guest Operating Systems
INFORMATION TECHNOLOGY 2014/10/19 10:43
http://technet.microsoft.com/en-us/library/cc794868(WS.10).aspx
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Windows Server 2008 (all versions, including R2 and SP1) - 1,2,3 or 4 Virtual processors (vCPU)
Windows Server 2003 (all versions, inluding R2) - 1 or 2 virtual processors
Windows 2000 Server with Service Pack 4 - only one (1) virtual processor
Windows 7 all versions including SP1 - 1,2,3 or 4 virtual processors
Windows Vista - 1 or 2 vCPUs
Windows XP SP3 - 1 or 2 vCPUs
Windows XP SP2 - 1 vCPU only, Windows XP x64 Edition with SP2 - 1 or 2 virtual processors