A New Mounting System:
Along with the new pin arrangement, AMD has also changed its heatsink retention system. As a direct result of this, there will be changes made to the cooling solution specifications. This doesn't change the dimensions of the cooler, but it does change the mounting mechanism used ever so slightly.
Socket AM2, Socket 939
Worry not though folks, as most heatsinks that used the previous heatsink retention system will still work on the new design - we'll come to the type that don't in due course. Higher-end heatsinks that don't use the retention bracket and attach directly to the motherboard will not fit, though. This is because AMD has changed the number of mounting screws on the retention system.
Instead of the two that were on all Socket 939, Socket 754 and Socket 940 motherboards, there are now four mounting screws. This was probably done to improve the stability of the retention system when heavier heatsinks are installed on the board. It is definitely an improvement over the older design, which relied on the retention bracket providing stability. The new design relies on screws through the motherboard for stability.
We hope that heatsink designers will release mounting system conversion packages, allowing older screw-to-the-motherboard heatsink designs to work on Socket AM2 motherboards. If heatsink manufacturers choose not to do this, many enthusiasts will be forced to change their cooling solution, even if it is only as a result of the changed mounting specifications.
One thing that we feel has changed for the worst though is the number of lugs at each end of the retention system - there is now only a single lug at each end compared to the three that were on the older retention bracket. However, there looks to be a new way to mount coolers, using the four clips that are right next to each of the four mounting screws. This is not confirmed at the time of publication, but the clips look robust enough to securely hold a heavy cooling solution.
Other heatsinks that will not work on the new retention bracket are heatsinks that were clip-locked onto the older retention system. Notice that the Socket 939/940/754 retention system has a fourth lug in two opposite corners. This was used for retaining certain spring-loaded cooler retention systems that some heatsink designers opted to use. These lugs are no longer on the new retention bracket, so you'll have to use a newer cooler in this scenario, too.