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

  • AndrejM - Friday, January 29, 2010 - link

    I think there were very few unlockable Athlon II X4's out there. I ordered one only a week after it was announced, and I couldn't unlock the L3 cache (on a gigabyte mobo with all of those unlocking options available). The performance is still pretty kick-ass for a 100$ chip without L3 Cache, if you ask me. Reply
  • leexgx - Sunday, January 31, 2010 - link

    i be very unhappy to get an binned Phenom II with its cache off been sold as an Athlon II X4, as the new Athlons II run so cool where as the Phenoms do not (the stock cooler is no good for the Phenoms it needs to be 2x bigger like the Blue Orb II works very well at keeping it at least warm) Reply
  • Jovec - Thursday, January 28, 2010 - link

    Using any AMD chipset motherboard with the SB750 South Bridge and proper BIOS support you'll have support for a feature called Advanced Clock Calibration (ACC).

    710 sb too, no?
  • Anand Lal Shimpi - Thursday, January 28, 2010 - link

    woops, you're right :) Fixed.

    Take care,
  • coolhardware - Sunday, January 31, 2010 - link

    Thanks for the tip Anand! I enjoyed reading the article so much that I decided to build my own :-). It came out to less than $200 for the entire system, though I used old memory and storage.
    CPU: X2 550 $90.99 (+$5 for NewEgg bundled cooler special)
    Motherboard: ASRock A785GMH/128M $69.99
    Case: ASUS TM-211 $25.00 (used eBay bucks for $20 worth of the total)

    Here's more info:">

    Any comments or build tips are appreciated!
  • Zebo - Tuesday, February 2, 2010 - link

    Nice. But....

    Fry's regularly has Phenom X2 II 550 + some mobo for less than $100!

    Just google "fry's Phenom X2 II 550"... you'll see. Some mobos support unlocking, some don't but many of us in CPU forums have known this is a greatest deal since November at least even without a Frys combo but with it it makes it insanely sweet.
  • blyndy - Friday, January 29, 2010 - link

    "Often times it's easier to just disable two cores and sell the chip for cheaper than you'd like"

    Wouldn't it be better to lower X4 prices slightly and dropping the X2s altogether?
  • MonkeyPaw - Friday, January 29, 2010 - link

    Yes and no. Not all X4s are likely to work, so there's still a reason to disable some cores and sell this product. The problem then is that they get more demand than they have CPU cores that need to be disabled, so they end up using lower quality functional quad cores to make X2s. Also, I think that AMD and Intel have strictest quality control. What they consider to be a bad core, we may never notice.

    It is still revenue either way, just not as much as they possibly could. Also, cheaper quads all around would only hurt AMD's total revenue. I'd guess that this X2 BE probably won't be around long as people start snatching them up. I do enjoy the little bones that AMD throws out there for the enthusiasts.
  • vyseus - Thursday, April 29, 2010 - link

    I've got a new System unit, can detect if it can unlock the core?

    -AMD Phenom II X2 555 3.2 Ghz BE
    -MSI 7599 770 - C45
    -Kingston DDR1333 (CL9.0) 2+2Gb
    -Gigabyte Superb 550w
    -500GB/32MB WD
    -Sapphire HD5670 1Gb ddr5

    If can really wanna try, I'm going to upgrade the heat sink to corsair H50, also adding few fans to the radiator of H50 and the casing..

    Can i try to unlock since I'm pretty new on overclocking, or i need a change of motherboard..Thanks in advance
  • talha - Saturday, May 22, 2010 - link

    Hey, I've written article about this too:
    Check it out and tell me if you like it...

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