Three days before Apple revolutio...wait, that didn't happen. I kid, I kid.

On Monday AMD updated just about all of its processor families with new chips in response to Clarkdale. We got the Athlon II X2 255, Athlon II X3 440, Phenom II X2 555 BE, Phenom II X4 635 and Phenom II X4 910e. All of the chips are in Bench, so if you want to know how they compare have a look - or check out our review.

There are two things I left out of that review that I felt needed following up on. First, let's take the Phenom II X2 555 BE.

If you read my take on the 555 you'll know that I don't really believe it's worth the price. Most users will be better off with a Core i3 530. There is just one exception I failed to mention: some Phenom II X2s can be turned into a Phenom II X4.

The technique is nothing new. Using any AMD chipset motherboard with a SB710 or SB750 South Bridge and proper BIOS support you'll have a feature called Advanced Clock Calibration (ACC). AMD introduced this feature back in 2008 as a way to improve overclocking on Phenom processors by sacrificing some sort of corner case stability for real world frequency headroom.

The Phenom II X2 is nothing more than a Phenom II X4 with two cores disabled. Originally these cores were disabled because of low yields, but over time yields on quad-core Phenom IIs should be high enough to negate the need for a Phenom II X2. This is most likely why AMD removed the Phenom II X2 from its official price list. It's also why the stranger Phenom II derivatives are also absent from AMD's price list. All that's left are Phenom II X4s pretty much.

A Phenom II X4 900 series die: 258mm2, 4-cores and a 6MB L3 cache. Also the basis for the Phenom II X2.

And herein lies the problem for companies that rely on die harvesting for their product line. Initially, the Phenom II X2 is a great way of using defective Phenom II X4 die. Once yields improve however, you've now created a market for these Phenom II X2s and have to basically sell a full-blown Phenom II X4 at a cheaper price to meet that demand. You could create a new die that's a dual-core Phenom II, but that's expensive and pulls engineers away from more exciting projects like Bulldozer. Often times it's easier to just disable two cores and sell the chip for cheaper than you'd like. At the same time you can do your best to discourage your customers from ordering too many. Remove it off the official price list, charge a little more for it, and direct people at a cheaper native alternative - like the Athlon II X2.

The Athlon II X2 die. Two cores are all you get.

AMD's sticky situation is your gain however. While I can't guarantee that all Phenom II X2s can be converted into quad-core chips, I'd say that your chances are probably pretty good at this point if you get a new enough chip. As with any sort of out-of-spec operation, proceed at your own risk. You may risk ending up with nothing more than a dual-core processor or an unstable quad-core. In my case however, my Phenom II X2 555 BE's extra two cores were easily unlocked.

My Socket-AM3 testbed uses Gigabyte's GA-MA790FXT-UD5P motherboard. In its BIOS there's an option for Advanced Clock Calibration. All you need to do is set EC Firmware Selection to Hybrid, and ACC to Auto:

Patiently waiting and a self-initiated reboot later and my CPU was identified as a Phenom II X4 B55 BE. Four cores running at 3.2GHz, just like a Phenom II X4 955 but for $99.

The chip also performs just like a 3.2GHz quad-core Phenom II, because it is one at this point:

Processor x264 HD 1st Pass x25 HD 2nd Pass
AMD Phenom II X4 965 72.1 fps 22.2 fps
AMD Phenom II X4 B55 70.6 fps 21.1 fps
AMD Phenom II X2 555 45.2 fps 10.9 fps


Overclocking is affected. With only two cores active my Phenom II X2 555 BE could run at 3.8GHz without any additional voltage. With four cores active, that number drops down to 3.6GHz.

My Phenom II X2 555 BE, with all four cores unlocked, and running at 3.6GHz.

If you're ok with the possibility of this not working at all, a Phenom II X2 555 BE with all four cores active is the absolute best value you can get for $99. AMD would like to charge you $160 for the opportunity, but you can put the savings towards a better video card or a shiny new SSD.

More Detail on the Phenom II X4 910e


View All Comments

  • 7Enigma - Friday, January 29, 2010 - link

    I think your best chances for successfully getting an unlockable chip would be to buy from a high-volume but low stock company (ie NOT Newegg and probably not even ZZF). Someone that does a lot of business so the chips aren't from last year, but just as importantly someone that isn't buying 10,000 at a pop and sitting on them. I don't know how Microcenters distribution chain works (do they have a huge warehouse that purchases in bulk, or is it more region-specific ordering), but they would seem to fit the bill if you're near one. Reply
  • jcgamo88 - Friday, January 29, 2010 - link

    I did purchase a 620 with intent on unlocking it. Was un able to do so on both a MSI GD70 and DFI 790fxb. :( Reply
  • Taft12 - Monday, February 8, 2010 - link

    It's like doubling down in blackjack - the payoff can be huge, or you might bust :)

    Now the question is can you resist buying another CPU to try again :D
  • sciwizam - Friday, January 29, 2010 - link

    Patientiently waiting and a self-initiated reboot later and my CPU was identified as a Phenom II X4 B55 BE. Four cores running at 3.2GHz, just like a Phenom II X4 955 but for $99.


    /typo police
  • MaDS - Friday, January 29, 2010 - link

    The Phenom II might prove incredible value for money when unlocked, and you consider it "THE best value for money" if done so, but as far as I'm concerned an L3-cache unlocked Athlon II X4 (if it works, ofcourse) fits the bill just as nicely and you get the added benefit of two extra cores in any case. So for people that can put 4 cores to good use, the Athlon II X4 might be the better buy.

    I unlocked my Athlon II X4 620, the full 6MB L3 cache is functional, rock stable and I can run it at 3.6GHz with a very slight voltage bump (and a not-top-of-the-line Xigmatek HDT-S1283 with silent fan).
  • Assimilator87 - Friday, January 29, 2010 - link

    The problem with the Athlon II X4, is that only a small number of them were Phenoms with disabled cache. Most of them are a different die that doesn't have any L3 cache at all. Reply
  • MaDS - Friday, January 29, 2010 - link

    Well, I don't know the passing rates for the Athlon II X4's versus the Phenom II X2's. If the passing rate of the unlocking of the X4's are really that low, the safest bet would indeed be the Phenom II X2.

    I'll just consider myself lucky then :)
  • StevoLincolnite - Friday, January 29, 2010 - link

    I'm another user who managed to get the cache unlocked on an Athlon 2 X4. :)

    Phenom 2 x4 910 performance at a much lower price, can't complain about that!
  • zarkness - Friday, January 29, 2010 - link

    May i know what is the batch of Athlon II x4 are u all using because i plan to buy one too... Reply
  • Taft12 - Friday, January 29, 2010 - link

    Almost surely it was the very first waves of Athlon II X4's could have their L3 cache unlocked. They needed to get a lot of these into the channel when the announcement was made since (unsurprisingly) a $99 quad-core CPU sold like mad out of the gate, and the non-L3 die production was just getting started.

    Unfortunately, your chances of buying a new Athlon II X4 that is cache-unlockable today are very low.

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