Hi there,
I did some looking around since i got a AMD FX-9590 (8 cores)
but noticed my fps was quite low in populated area's and noticed wow used 4-6 cores out of the 8 available.
I remembered seeing a post on the official wow forums about this issue and did some digging,
now finally i have wow using all 8 available cores :)
This is the "thing" that influences the amount of cores your client will use: processaffinitymask.
this. under normal circumstances is automatically assigned by your client itself with the first startup of the game.
You can change the value in your world of warcraft/wtf/config.wtf file.
Changing the value can help your game run better but also A LOT slower so be careful with what you do. (best to backup your config.wtf)
how to set Processaffinitymask:
Basically tells your PC which cores to use.
The values:
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To change this:
go to your config.wtf and edit it with notepad or notepad++ both work.
If you see this line: SET processAffinityMask "x"
replace the X with one of these values given above.
If you cant see the line, simply Copy, or Type it with the correct value.
How to know if your client uses which cores
There are addons that monitor these things, yet i do not know what their names are, probably 5 minutes of googling will help a lot.
However if you are using windows 10 (and i think its the same in 8)
you can just open your Taskmanager> Click on more details> Go to the Processes tab> CPU>
if you see one graph, rightclick and select (Change graph to> logical processors) >
Start up your client, login and when you load your character hover your mouse over the last core(s),
if you see a small popup windows saying "CPU x Parked" it means windows is not utilizing it. (then this quide will work)
I hope this Guide helped you, in case you still have questions, try reviewing one of the given sources and or ask it in this thread.
Sources
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