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

Digging For Clues...

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 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.

Chris Angelini
Chris Angelini is an Editor Emeritus at Tom's Hardware US. He edits hardware reviews and covers high-profile CPU and GPU launches.
  • dirtmountain
    Good article. Now if you can just get your ad clowns from sticking us with those annoying ads.....!
  • test them with games... some people care about that :P
  • cangelini
    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.
  • 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)
  • tacoslave
    i like this article toms should do more stuff like this.
  • apache_lives
    Page 3 "it ran for an hour sans error before we shut it down" - mistake?

    Me wonders if extra v's would help both to the memory, HTT and cores etc, or underclock that extra core if possible....

    On the other hand as all overclockers/modders should be aware THERE'S NO GUARANTEE on what you can get out of your hardware etc.

    Out of interest, is the third core ("Core 2"... LOL) still always the culprit of every X3 (unlockable or not)?

    Now if only there was some super secret on modding my Q6600 into a i7 940.....
  • cangelini
    Hey Apache! No error, sans = without.
  • apache_lives
    still reads wrong to me?
  • Summer Leigh Castle
    Good article but can someone explain how ACC % works? Also, where do we start in terms of ACC % if we're tweaking for stability?
  • ravenware
    cangeliniHey Apache! No error, sans = without.
    The only reason I know that is because of Wayne's World2.