From Tom's Hardware:
"As soon as Microsoft Vista arrives, things will change a bit. Windows XP is unable to tell physical processors apart, and it will distribute the processing of threads to all CPU cores as they are available. Whether the cores are located on one, two or multiple CPUs is irrelevant here, which can cause inter-processor thread-switching. This should be avoided, as it might entail the relocation of thread data as well - isn't that a nice new bottleneck!
Threads that were processed on one physical core might be handled by a different unit the next time they are being executed. If you now think of an Intel quad core created by putting two dual core processors into one physical processor package, you will realize that the Front Side Bus is the only way for inter-processor communication and main memory access.
In a worst case Windows XP scenario, processing unit A has to wait until unit B completes memory access. Then A accesses the memory to fetch data, which it stores in its L2 cache to provide it locally for processing. If, however, Windows assigns the thread to CPU B, it will have to fetch the current data from A's L2 cache, causing additional Front Side Bus traffic. For coherency and performance reasons, data cannot be fetched from the main memory again at this point, since it was already processed. In the end, all of the elements involved are slowed down by this manoeuvre.
Windows Vista Ultimate Edition will be able to tell processors or nodes apart from simple processing cores. This allows the operating system to assign threads in a more resource-efficient manner: one large task can be executed exclusively on CPU A, while another huge workload runs autonomously on CPU B. Inter-processor task switching is eliminated due to the enhanced hardware awareness of Vista Ultimate, and performance will scale much better with increased core count per processor."
Does this mean that all other version of Vista have been hobbled on the performance front? That's astonishing if this is the case
