Wonderful for desktops, but nice for laptops too:
Basically there is a semi-hidden feature of Athlons so they can save power and keep cooler.
The problem with it is that it effects some applications (http://vcool.occludo.net/VC_Theory.html). "Well during my testing I found out that disconnecting the system bus might affect real-time applications, i.e. applications that use hardware in a time-critical way. For example I noticed that with the bus disconnect enabled a captured video is full of dropped or garbled lines. So this cooling feature comes at a cost - probably that's why they kept it hidden."