Socket AM2+ and AM3

Socket AM2+ and AM3

In our initial Phenom II review I already stated this, AMD has an approach that I like to see very much. That is trying to stick as long as they can with a processor socket design. Therefore the good news is, if you have an AM2+ compatible 790 chipset motherboard already, that you can pop in a new AM3 processor and it'll work. There is no need to purchase a DDR3 motherboard whatsoever.

Mind you that if you do so, and this is a very strong recommendation, upgrade your system BIOS (motherboard BIOS) for Phenom II compatibility. Typically this boils down to an AMD 780/790 chipset purchased last year. For AMD 780 chipsets there is a second restriction, please do make sure your motherboard can handle the power requirements of the processor. Please check this with your motherboard manufacturer.

What is the deal about Socket AM3 then?

This socket change was needed for merely one thing, to achieve DDR3 memory support.

As an example: today's processor used is a Socket AM3 processor. It fits fine on Socket AM2+ motherboards which support Phenom II. The only snag is that you are forced to use DDR2 memory, well.'.. that is not really a negative thing as DDR2 memory is intensely cheap to purchase.

Say you take DDR2 1066 with fast timings, opposed to 1333 MHz DDR3 memory typically with slightly slower timings. The performance advantage for DDR3 would very dismal.

Bottom line:

• AMD AM3 processors will work on most AM2+ motherboards (780/790 chipset | latest BIOS mandatory).
• AMD AM2/AM2+ processors will not work on AM3 motherboards because AM2 processors lack a DDR3 memory controller.

Two extra pins (940 for AM2+ vs 938 for AM3) makes the older chips mechanically incompatible with the new socket, preventing users from attempting to install an old chip in a new board.
So if you want to go for DDR3, the processor's memory controller can manage that as well. A migration towards a Socket AM3 motherboard is then mandatory. Once you do have a Socket AM3 motherboard, you'll get support for up to DDR3 1333 MHz memory. On socket AM2+ you'll be able to make use of DDR2-1066 MHz memory, while on socket AM2 you'll be limited to 800 MHz.

Socket AM3 in plain sight, as well as four DDR3 DIMM slots.