[citation][nom]Fokissed[/nom]The number is calculated with binary addition, you can specify which cores you want WoW to use by setting the affinity mask to the binary number that represents the cores used:core0 - 1 (2^0)core1 - 2 (2^1)core2 - 4 (2^2)core3 - 8 (2^3)core4 - 16 (2^4)core5 - 32 (2^5)Add these numbers up to get the affinity mask that suits the processor😀ual core - 3 (11)Tri core - 7 (111)Quad core - 15 (1111)Hexa core - 63 (111111)Using binary numbers as boolean values for each core (right to left) will convert into the affinity mask needed to use those cores.[/citation]
Back in the day, before patch 2.3, when this was needed, the setting for Core 2 Quads would be "15" and Core i7 would need "85" to avoid using the HT cores. However, setting any computer to "255" would cause it to use all available cores. So, that setting was the easiest.
However, that setting was no longer needed after patch 2.3. Blizzard defaulted to using all available cores at that point, but was limited to 4 threads, or 4 used cores. This setting was used frequently after that on Core i7 machines because it would sometimes use a HT virutal core and its corresponding physical core. (i.e. it would use processors 1, 2, 4, and 7, skipping cores 5 and 6 and limiting performance to three physical cores.)
In patch 2.4, this changed. It used the 4 cores much more prudently and stuck with physical cores only. It would detect HT virtual cores and avoid them.
In patch 4.0.1, they spread out the program to use more threads, and now makes use of all available cores up to 32. So, a dual 6 core Xeon would have 24 cores and they would all be used. They just use them to a much lesser degree.
No settings are needed to change this, but turning off HT can help performance a little.