Windows 7 doesn't detect all CPU cores?

Because Windows 7 has been running well on my computer, I have installed it on my next door neighbours computer so he can try it. He has a Q9550 processor and it works well in Vista with Task Manager showing 4 cores.

When we tried Windows 7 it only shows 2 cores, even though this is a quad core CPU (not dual core).

If the computer boots back into Vista it shows all 4 and it works fine, so I don't think it's a hardware problem. Updating the BIOS didn't change a thing either.

That's strange, did it do it from a clean install? Try running msconfig from the start menu (as an admin).

Then click boot > advanced options > then click Detect HAL and set the number of processors at 4.

Once you restart, that should do the trick

Thanks. Went round to my neighbours last week and tried this, and it worked straight away. Do you know why it needs to be set manually, I thought it should be able to work out of the box?