AMD Upgrade Paths

While many are thinking about upgrading an AMD AM2 motherboard, there is a story on Ars Technica concerning the availability of AM3 CPUs coming down the pike, which will be a much better choice for anyone wishing to get more performance, and greater energy efficiency. A side benefit of the proposed solution is a possible lengthening of the CPUs useful life.

What is meant by this is that when the new 45nm chips start rolling out from AMD that are designated AM3 (current ones released just before CES are AM2+ parts) they will be also usable in AM2 and AM2+ motherboards, with a BIOS update. Now some manufacturers will want to sell new motherboards, so the motherboard you own might never get that update released, but if that is the case, third party BIOS manufacturers just might start selling a fix for these orphaned boards. The AMD 780G boards will be the ones that are possibly in doubt, as far as I am aware, the 790 chipset boards are already being touted as capable, with the attending promise of BIOS updates without problems.

The benefit of the AM3 part is three-fold. First, the parts will be faster, as swapping even lower speed chips will show increased performance through greater work done per clock cycle, as well as increased cache on chip, allowing more data to fit on chip and resulting in fewer calls to main memory. Second, the chips will use less power, which means that motherboards that might not have been capable of use with AM2+ Phenoms simply because of power dissipation (heat buildup on motherboard parts) will allow the use of Phenom IIs that fall within the thermal envelope of that motherboard.  Third, when prices come down, or the economy picks up, or both, the CPU will simply drop in to an AM3 motherboard (which by definition means DDR3) and then the user will get another speed bump, as if the CPU had gotten faster when the motherboard was changed.

from AnandTech

“Socket-AM3 Phenom II parts will also work in Socket-AM2+ motherboards, the two are pin-compatible. When in an AM2+ board, these upcoming Phenom II processors will work in DDR2 mode, but when in an AM3 board they will work in DDR3 mode. How cool is that?

This unique flexibility is largely due to the work that was done on the DDR2 and DDR3 specs at JEDEC. The number of signaling pins and the signaling pins themselves between DDR2 and DDR3 don’t actually change on the memory controller side; the main differences are routing and termination at the memory socket side. AMD just needed a physical memory interface on Phenom II that could operate at both 1.8V (DDR2) and 1.5V (DDR3) as well as work with timings for either memory technology. The potential was there to do this on the first Phenom, it just wasn’t ready in time, but with the Socket-AM3 Phenom II processors you’ll be able to do it.”

from Ars Technica

The compatibility, however, only goes one way; Socket AM2/AM2+ CPUs are not compatible with Socket AM3 motherboards. As for the relationship between AM3 and DDR3, that’s a tad less clear. On the one hand, Socket AM3 has always been billed as a DDR3 chipset; one reason Socket AM2/AM2+ processors are incompatible with Socket AM3 is because they lack a DDR3 memory controller. Said incompatibility will always exist for physical reasons—AM/AM2+ processors have 940 pins, compared to just 938 on an AM3. If the full-fledged push towards DD3 is delayed, however, it raises the question of whether or not we might see AM3 motherboards using DDR2. (There will be no hybrid DDR2/DDR3 boards for trace length and latency reasons).

So for many, it makes a bit of sense to hold off on an AMD CPU purchase until the parts stated AM3 (and can use DDR3) are available. The wait will allow manufacturers to size up whether they will offer the BIOS updates necessary, and also allow AMD to get the clock speeds up, as well as efficiencies.

Patience is a virtue, and may hold great benefits!

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