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Digging For Clues...

Phenom II: Unlocking Cores, Cache, And A Free Lunch
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Cores And Caches

It turns out that the X3s aren’t the only models with aspirations to something higher. AMD’s Phenom II X4 800-series chips—the ones with a 4 MB L3 cache instead of 6 MB—can also be unlocked using the ACC trick, though the value there is even more questionable. A Phenom II X4 810 costs $167 on Newegg right now. A Phenom II X4 920 running 200 MHz faster is priced at $189. Granted, the 810 is an AM3 part while the 900s are currently AM2+, but AMD will be updating its Socket AM3 lineup soon with higher-end models, so there’s no reason to rush into AM2+ if you’d rather make the move to DDR3.

Let’s check out some real hardware though, and see if we can improve our odds of a stable configuration using these less-expensive processors. It goes without saying that, even at stock speeds, what we’re doing here is on the same level as overclocking. Nobody is going to support you on this project, except the community. If you run into problems, check in with the forums before going to AMD or your motherboard vendor. Neither of them are going to look fondly on this little experiment.

Not All Motherboards Need Apply

Our first order of business was settling on a platform for testing. We already know that ASRock and Biostar are the two vendors from where this capability originated. And we’ve already seen users asking on our forums about how to do this.

We started by testing Asus’ M4A79T Deluxe, which we’ve seen on other forums claimed to work. No-go, though. With ACC disabled, the board functions fine. Turn it on, and our known-unlockable Phenom II X3 720 blue-screened consistently. We were already using the latest BIOS from Asus, so we swapped in another board with an older BIOS loaded.

Next up was Gigabyte’s MA790XT-UD4P. We received that board with BIOS F2, from January 16th. That didn’t help unlock our “sure thing” Phenom II X3, though. On March 10, Gigabyte released a BIOS F2B, which was supposed to “Update ACC code for Phenom X3 CPU.” We updated to BIOS F3—the latest—and tried again. Still nothing.

We contacted Gigabyte to explain what was meant by “Update ACC code…” According to the company, all vendors developing new BIOS’ with AMD’s latest microcode will be disabling the core/cache unlock, which at least explains why the recently-updated ASUS and Gigabyte boards weren’t cooperating. Why not continue using the old microcode? The latest software fixes other issues too, like a reported random reboot issue. In the eyes of a motherboard vendor, rolling out the latest stability fixes takes precedence over an unsupported and potentially problematic hardware hack. If you want to maintain that tweaked Phenom II, you’ll need to stick to a pre-fix BIOS. 

ASRock's M3A790GXH/128M, the only board in our lab still able to unlock the PhenomsASRock's M3A790GXH/128M, the only board in our lab still able to unlock the Phenoms

Finally, we tried the one board that we knew would work: ASRock’s M3A790GXH/128M. Sure enough, with ACC on and set to Auto, the board made the Phenom II X3 720’s fourth core available in Windows. ASRock has only released one BIOS for this board—its launch version. Is it only a matter of time before an update comes out and everyone who upgrades loses their unlock capability?

Representatives at ASRock say the company isn’t in a hurry to phase-in the latest microcode updates. Should AMD launch a new processor or fix bugs that the company considers critical enough to necessitate the update, it plans to maintain two BIOS versions, allowing enthusiasts to choose one or the other.

Not All CPUs Need Apply, Either

In all, we tested three Phenom II X4 810s and three Phenom II X3 720 Black Editions. One each came from AMD during our initial round of sampling. One each came from ASRock—these were our “sure things,” which we knew would serve as suitable references for confirming boards that would or would not work. The final pair was purchased online from Newegg in an effort to get at least a basic idea for how feasible it’d be to get an unlockable processor at retail.

Of course, the two CPUs from ASRock worked (sort of—more on this in a second). The Phenom II X4 810 from AMD worked. The Phenom II X3 720 BE from AMD did not work. The Phenom II X4 810 from Newegg worked. And the Phenom II X3 720 did not.

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Top Comments
  • 13 Hide
    cangelini , April 16, 2009 7:15 AM
    Well, but the point isn't the benchmarks. We already know that most games are going to be limited more by graphics horsepower versus whether a CPU has three or four cores/4MB shared L3 or 6MB shared L3.

    In fact, when it comes to gaming, you're going to be better off looking for the fastest overclock possible with your three good cores or 4MB of known-good cache, really.
Other Comments
  • 7 Hide
    dirtmountain , April 16, 2009 6:49 AM
    Good article. Now if you can just get your ad clowns from sticking us with those annoying ads.....!
  • 2 Hide
    Anonymous , April 16, 2009 7:09 AM
    test them with games... some people care about that :p 
  • 13 Hide
    cangelini , April 16, 2009 7:15 AM
    Well, but the point isn't the benchmarks. We already know that most games are going to be limited more by graphics horsepower versus whether a CPU has three or four cores/4MB shared L3 or 6MB shared L3.

    In fact, when it comes to gaming, you're going to be better off looking for the fastest overclock possible with your three good cores or 4MB of known-good cache, really.
  • 1 Hide
    Anonymous , April 16, 2009 7:28 AM
    omg you replied to me... i'm so honoured :p 

    but yes, i agree... but if you had crossfire gpus, this would make a difference. but then again, i think you'd have the money to buy the real thing (phenom II 920)
  • 5 Hide
    tacoslave , April 16, 2009 8:13 AM
    i like this article toms should do more stuff like this.
  • 2 Hide
    cangelini , April 16, 2009 8:26 AM
    Hey Apache! No error, sans = without.
  • 2 Hide
    Summer Leigh Castle , April 16, 2009 9:05 AM
    Good article but can someone explain how ACC % works? Also, where do we start in terms of ACC % if we're tweaking for stability?
  • -1 Hide
    ravenware , April 16, 2009 9:22 AM
    cangeliniHey Apache! No error, sans = without.


    The only reason I know that is because of Wayne's World2.
  • 0 Hide
    cangelini , April 16, 2009 9:23 AM
    I do wish I could give you more detail on ACC, but AMD has played that card close to its chest. In terms of where to start, I'd say "Auto" is your best bet, and then move up and down in 2% increments in each direction.
  • 0 Hide
    raden_muaz , April 16, 2009 11:09 AM
    can you compare it with PII 910? PII 810 have higher clock speed.
  • 9 Hide
    Slobogob , April 16, 2009 11:10 AM
    Great article. Reminds me of how Tomshardware used to be.
  • 3 Hide
    empstar , April 16, 2009 11:59 AM
    this reminds me of the 1st Athlon with gold finger and the athlon with the "tape" on top to link connection for Socket A. 1998 I start reading this web..... :-) where is Dr. Toms P go ? I wonder..
  • 0 Hide
    apache_lives , April 16, 2009 12:08 PM
    tom sold it ;) 
  • 0 Hide
    empstar , April 16, 2009 12:19 PM
    sold it to Bestofmedia? omg since when?
  • 0 Hide
    Pei-chen , April 16, 2009 12:24 PM
    AMD is not overclocker friendly by locking the multiplier, cores and cache. What happened to the AMD in Athlon and Athlon XP era?
  • 2 Hide
    apache_lives , April 16, 2009 12:55 PM
    Pei-chenAMD is not overclocker friendly by locking the multiplier, cores and cache. What happened to the AMD in Athlon and Athlon XP era?


    its called sales - if your $100 processor was the same as your $500 processor why would you buy the $500 processor?
  • 1 Hide
    neiroatopelcc , April 16, 2009 1:31 PM
    I supposed it wouldn't be impossible to custom tailor a bios for a non asrock board. I haven't dared try (nor needed to), but I expect it to be quite likely you could just extract the microcode from an older, working, asrock bios, and replace the code in your gigabyte, asus or whatever bios with it. All I think that is required, apart from knowledge on bios tinkering I don't have, is a 750 chip on the board.
  • -1 Hide
    apache_lives , April 16, 2009 1:38 PM
    i believe it depends partly on the IO chip too (usually one of those ITE 87xx chips), then flash part type, rom size, bios brand (award, AMI etc) - beyond most of us and more for the motherboard engineers etc.
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