Randall C. Kennedy, in Page 3 his article, The generation gap: Windows on multicore, says:
But it’s not all bad news with Windows 7. Microsoft’s new OS has a clear multicore scalability advantage over both Windows XP and Windows Vista, especially on less I/O-bound tasks like our multiprocess database workload. (We can thank SQL Server 2008 [...]
Interesting tidbit about Windows 7 performance