SQL Server only using 4 out of 6 cores

Hi,

I noticed that SQL server only appears to be using 4 out of 6 cores.

I was doing a bit of reading around this and I think the solution may be to change some of the processor affinity settings. Has anybody got any advice on recommended settings, pitfalls when changing processor affinity and any useful links if you have them?

Oh, also if there's anything else that may be causing this I'd be keen to know.

Cheers

Paul