ok a friend told me that XP 64bit will not use a quad core processor efficiantly. Where as vista will?

Any thoughts? I have a AMD Phenom 9550 Quad Core 2.20 running XP 64 bit

and have been considering moving over to Vista 64bit thoughts?

The effectiveness of a quad depends on the available software. Some Vista software is designed to include quad functionality. In as much as Microsoft has stopped supporting XP, software developers are not going to put resources into an unsupported operating system.

Therefore, by process of elimination, subject to the full release of Win7, Vista is the only option left. And, even after Win7 is released, it will probably take a few years before we see Win7 software supporting quads. I think it depends on how close Win7 is to Vista software wise.

Even with dual core system, for most applications, when you look at a core monitor, you can see the one CPU knocking it's brains out and the second CPU barely being accessed. The same applies to quad systems. It all depends on if the software truly takes advantage of the four processors or simply can run on a quad system.

Hope that helps.