Socket-AM2, AM2+ and AM3: Backwards Compatibility

AMD fixed the cache size issue, it fixed the power consumption problem, and we even got higher clock speeds with Phenom II. What I didn’t expect was something more. AMD has always been a manufacturer for the customers. Over the past couple of years the problem has been that their processors haven’t really been desired by consumers, but prior to that the AMD that we know and love designed processors for today’s applications with a minimal number of platform changes between processors.

Phenom II carries AMD’s consumer focused nature to the next level. Today’s Phenom II parts are designed for Socket-AM2+ motherboards. AMD doesn’t qualify any of them for use on Socket-AM2 motherboards, but there’s nothing stopping a motherboard maker from enabling support on a standard AM2 motherboard. You will need a BIOS update.

Next month, AMD will launch the first Socket-AM3 Phenom II processors. The main difference here is that these parts will support DDR3 memory. Oh no, another socket, right? Wrong.

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.

While I’m not sure how practically useful the AM3/AM2+ flexibility will be, I’d rather have it than not. Being able to take one CPU and stick it in two different sockets, each with a different memory technology, and have it just work is the most customer-centric move I’ve ever seen either company make. AMD told me that this plan was in the works before the original Phenom ever launched, somewhere in the 2004 timeframe. AMD was active in JEDEC on making the DDR2 and DDR3 specs similar enough that this one-CPU, two-sockets approach could work.

One of the biggest risks AMD faced when it chose to integrate the memory controller was what would happen if there was a sudden shift in memory technology. With the upcoming Socket-AM3 versions of Phenom II, that risk is completely mitigated by the fact that a single chip can work with either memory technology. It gives OEMs a tremendous amount of flexibility to ship systems with either DDR2 or DDR3 memory depending on which is more cost effective. It also ensures a much smoother transition to DDR3.

The downside for AMD is that because Socket-AM3 Phenom II chips are right around the corner, it makes little sense to buy one of these Socket-AM2+ Phenom II processors - at least not until we know the pricing and availability of the Socket-AM3 versions.

Slower North Bridge Frequency for AM2+, Faster when AM3 Arrives

An extra benefit of the Socket-AM3 Phenom II processors is that their uncore (memory controller + L3 cache) will be clocked at 2.0GHz instead of 1.8GHz like the two processors launching today. By comparison the Phenom 9850 and 9950 both have a 2.0GHz uncore clock; AMD had to go down to 1.8GHz to launch the Phenom II at 2.8GHz and 3.0GHz today.

As 45nm yields improve AMD will increase the uncore frequency, but today it's at 1.8GHz and the AM3 chips will have it at 2.0GHz. The Core i7 runs its uncore at 2.13GHz for the 920 and 940, and 2.66GHz for the 965.

45nm and Low Power Consumption Phenom vs. Phenom II - Clock for Clock


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  • Walkeer - Thursday, October 15, 2009 - link

    Super, so because MS Vista has a really bad and stupid CPU scheduler, AMD had to disable perfectly legit and smart power saving feature = CnC per core rather than per chip. I really love windows! I expect that CnC per-core caused no problems under linux for example.... Reply
  • CuE0083 - Sunday, April 26, 2009 - link

    I have been a reader of this site for a few years (first time commenting) and I just wanted to know how you guys determine that a particular processor is a good overclocker.

    1) Do you guys try overclocking multiple chips?
    2) Do you just walk into the store, pick a random chip, and try overclocking it?
    3) Or does AMD send you a chip?
  • v12v12 - Thursday, July 23, 2009 - link

    All this bickering and nick picking—when to me the solution seems simple.

    All the poor folks clamoring about numbers they COULD NOT EVER POSSIBLY tell the difference if using Intel Vs AMD in a dboule-blind test! None of you can tell the measurable diffs in FPS and temp. It's all little programs with numbers telling you there's a difference. So wtf is all the fus about?

    Phenom-II is for people that already have an old AM2 rig and want to upgrade. But you forget that your old, slow ass mobo chipset and antiquated ram wouldn't even come close of a newer Intel system period.
    A Brand NEW Phenom-II would "compete," but it barely does that. And as prices drop Phenom-II is losing even more ground as someone with an intel 775 can spring for a fast Quad-core, while you're stuck with the SAME OLD MOBO and RAM DERRRRR?
    Stop all the nit-picking and bemoaning over Intel.

    Does it make sense to scrap your current AMD rig for a completely new Intel unit?

    YES = If you're doing video/AV editing and plan on getting an i7/i5 or if you’re not broke!

    NO = If you currently have an AMD and need some extra horse-power.

    But to falsely rationalize your purchase/mindset by suddenly putting the i7 into the "it's SO expensive" BS category; you're BROKE, you have no say about price. Get a real job and stop spending money on other nonsense and SAVE up like smart people do. It's YOUR own fault you cannot afford a damn $1100-1400 computer: that's NOT a lot. Just b/c YOU cannot afford it doesn't mean there's something "wrong" with i7.

    You're comparing a 2yr old Q6600 against AMD's newest unit LOL? That's like a car magazine comparing the newest lambo to a 2 year old Ferrari etc. BUT PRICE OMG... Prices steadily go DOWN, thus folks with 775 can still upgrade to 6700, 6800 and so forth.

    I'm glad AMD is "sort of" showing a rally to CATCH UP... BUT... when you buy into INTEL you're buying into a PROVEN ROADMAP OF PERFORMANCE VS AMD: you're buying into a mystery grab-bag of performance PROMISES.

    Geesh. Just get the Phenom-II if you cannot afford the i7. Nobody with sense is talking about going from a Q6600/9xxx to 2 year behind the pack Phenom. This is just sophomoric nonsense.

    Common-sense would tell you:

    1) GET A BETTER JOB (education/certs etc)

    2) Stop spending money on other hobbies and misc junk

    3) STFU already and improve your financial situation, THEN you have a say. It's YOUR fault you don't have enough for a paltry $1200 machine. WHO doesn't have $1200? If you don't you haven't EARNED the right to complain. Complain b/c it's someone else's fault - I'm betting it's mostly your own lack of saving & discipline that's the problem.

    None of you may like or agree w/me, but guess what? I don't care b/c I HAVE $1200 to spend so Fsck it I'm happy. Stop drinking, doing drugs, going out, blowing money on cable-TV and crap, for a change? Most of you are guilty of 1 or more of these frivolities.

    Honestly THINK about what you’re saying here? You’re complaining about a superior i7 that is too expensive to do WHAT— play some damn video games? So your rationale is to do what? Buy a new or CPU upgrade to do the same? So THUS instead of continually saving to get the best… You BLOW your loads for inferior technology… and so the cycle continues. You’re NOW BROKE AGAIN and behind. Maybe you’ll start saving once again and come out of the wood work 2-3yrs later and STILL be complain once again “OMG it’s TOO EXPENSIVE” “I’ll by the cheap crap instead!”

    LMFAO NOW THAT IS Ludicrous!
  • goofbud - Tuesday, December 6, 2011 - link

    Are you serious dude?

    It ain't the money. I know. I have money. I also have a lambo a porche and an evo. I like testing AMD because they give us "certified" techs something to tinker with and work on. AMD is a brand for builders and true techs like to tinker with a processor and see how far it can go. Even when I was in high school I owned 486's which were the latest and greatest that time. I had an INTEL PC and it sucked dirt once Microsoft came out with windows. Maybe Intel is ahead now but AMD is catching up. They can create the ultimate processor but they don't have to. Not yet.

    BTW, watch how you talk. Be considerate. It ain't the money man. I can afford to buy as many alienware pc's I want. But I don't. Am I a gamer? Yes! I have a powerful system now and am happy I did not spend a lot of money on it. See, this is the thing. If you are smart you just don't want to buy the fastest CPU and fastest RAM that comes out. It's like buying an PS3 for $6,000.00 on ebay just because you want to be the first to play it. That is stupid.

    People buy AMD because they are tweakable. They try to buy the cheapest parts out there, tweak it, and see how far it can go. Makes sense?

    So what if you have the fastest computer in the world. If you don't use it everyday you just wasted money.

    Understand now kid. Now STFU and Go to your room!
  • sandstones - Wednesday, March 25, 2009 - link

    I know that we should look at relative sysmark scores, but I'm still puzzled by the higher scores in this batch of tests, compared to those done in April 2008.

    For example the top performer from April - Core 2 Duo E8400 got a score of 161 on Overall in April 2008, and 191 in Jan 2009. The X4 Phenom 9750 went from 126 to 148. Other CPU's in both tests had similar differences. That's a bigger percentage difference than what gets used to debate whether Intel or AMD is better.

    Anand - any comments on what caused such a large difference?
  • Amitjakhar - Friday, February 20, 2009 - link">
    After overclocking it really comes near and sometime it gets better performance them Core i7. Which is good. AMD has done superb job and they are in the right direction. Next black edition will make Intel so worry they have to go to work again.
  • Amitjakhar - Friday, February 20, 2009 - link

    Phenom II is showing power much better then here. To me it seems they have not done the testing properly. You better check out this link and find how its performing genuinely">
  • salem80 - Tuesday, January 27, 2009 - link

    The Q9400 are 126W~174W not like what Intel said 95W ?
    even E8600 (124W~157W) while they say 65W ?
    their huge deferent in numbers here .
  • pcuser123 - Saturday, January 24, 2009 - link

    I think the new i7 core sucks compare Phenom II. Just look at the pricing vs performance on those two.
    Here is the benchmarks">
  • gipper - Monday, January 19, 2009 - link

    You do the overclocks but don't show us the results? Following overclocking, those stock processors have WIDELY different capabilities.

    I'd love to see those video encode charts redone with the overclocked processors. That would tell me the TRUE value of the 64x2BE, C2D, Phenom, PhenomII, and i7 relative to one another.

    Otherwise, your overclock information borders on worthless.

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