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Tweaking the Phenom 9600 Black Edition

AMD unlocks its top quad, and we do the obvious
— 3:35 PM on February 12, 2008

The Phenom 9600 Black Edition has been knocking around in Damage Labs for a while now, and I'm afraid I haven't done it justice. The Black Edition is an intriguing product in a number of ways, because it's a relatively affordable quad-core processor with an unlocked upper multiplier for easy overclocking. AMD has had its share of trouble with the Phenom, from delays to the clock frequency problems to the infamous TLB erratum, but the Black Edition is a very nice olive branch that AMD has extended to enthusiasts—and it may warrant your consideration, especially if you're already running a Socket AM2-based system.

My original plan was to publish a full-blown review of the Black Edition, complete with a full set of benchmark results for the processor both with and without the TLB erratum workaround enabled. As I've noted elsewhere, though, that's actually happened already, since I included those numbers in my Skulltrail review. What you'll find there are scores for the Phenom 9600 at stock speeds with and without the TLB workaround, along with our first power efficiency tests for the Phenom with Cool'n'Quiet dynamic clock throttling working properly. The results confirm our initial impressions of the TLB workaround's impact—it's sometimes quite devastating—and illustrate that the workaround can degrade performance in games, as well. Even with the workaround disabled, the Phenom 9600 at stock clock speeds can't quite keep pace with its most direct competitor, Intel's Core 2 Quad Q6600, in terms of overall performance.

So we already have the stock performance picture for the Phenom largely covered. The Phenom 9600 Black Edition, though, remains one heckuva playground for tweaking and tuning. Let me briefly share with you some of my experiences with it, including my overclocking exploits.

OverDrive or BIOS?
If you're using a motherboard based on AMD's 790FX chipset, tweaking the Black Edition will probably start and end with AMD's nifty OverDrive utility, although you may take a few detours in between.

The first thing most folks will want to do with OverDrive is disable the TLB erratum workaround. As we've explained elsewhere, AMD says the possibility of the erratum causing a crash doing the kinds of things that desktop PCs tend to do is very remote, and we believe them. If you're already accustomed to risking some possible system instability by overclocking your CPU, you're probably a good candidate for, uh, going commando and running without the TLB workaround. And, in truth, you're not going to want to buy a Phenom right now, prior to the arrival of new chips with a proper fix for the erratum, unless you're willing to run without the workaround. The Phenom's performance with the workaround enabled just isn't attractive.

AMD has recommended that PC vendors enable the workaround by default, which it surely felt obligated to do because consumers (rightly) expect "100% stability" out of a processor. The firm has also recommended that motherboard makers update their BIOSes to include the TLB workaround with no option to disable it. But AMD has left a loophole in its OverDrive utility, the one officially sanctioned place where users can disable the workaround.

Unfortunately, they've left it almost entirely undocumented. The button for disabling the TLB workaround sits in the top right corner of the utility's main window with no labeling unless you hover the mouse pointer over it. Then you'll see what's shown in the picture to the right: "When this button is yellow or red, your system enters into boost mode." That's all you get. AMD tells us that what's happening is this: whenever the button is yellow or red, the TLB workaround is disabled. When the button is red, the utility also disables a power management option on the CPU, which can boost performance a little bit more.

I don't understand AMD's approach here. If they're going to provide a means of disabling the workaround, I'd think they'd want to be entirely clear with users about what the utility is doing and what the risks are. Heck, the rest of OverDrive's tweaking options are incredibly detailed and clearly labeled, right down to the most obscure memory timing options.

I ran into another issue with OverDrive's TLB workaround switch. I hesitate to mention it simply because I haven't had time to investigate it fully, but it merits a mention. I tried using OverDrive to disable the TLB workaround during some of my performance testing, using Vista x64 and an MSI K9A2 Platinum motherboard, and I found that the switch didn't always seem to work as advertised. Disabling the workaround via OverDrive generally yielded performance below what I could get by using a BIOS that didn't include the workaround. In some cases, performance didn't improve at all with the "Turbo" button in OverDrive set to yellow.

The good news is that mobo makers seem to be engaging in a bit of civil disobedience with regard to the erratum workaround. Asus provides a clearly labeled option for enabling and disabling the workaround in the M3A32-MVP Deluxe BIOS, and in the version of the BIOS I tried, the workaround was even disabled by default. Intriguing. On the MSI board, I completed my performance testing simply by flashing back to an older BIOS without the workaround. Later, I was able to hunt down a beta MSI BIOS on the Internets that includes a workaround switch, as well. Given everything I've seen, I think using a BIOS-based switch is the best means of disabling the workaround.

That's especially true, of course, if you have a Socket AM2 motherboard that's not based on an ATI/AMD chipset, since OverDrive won't work on those boards. Since the Phenom's launch, the upgrade prospects for current owners of AM2 motherboards have been cloudy, to say the least. As I write, AMD's motherboard compatibility list for the Phenom includes 17 motherboards, and only five of them are based on Nvidia chipsets.

To test the waters, I flashed the BIOS on my Asus M2N32-SLI Deluxe motherboard, a mobo based on the nForce 590 SLI chipset that does not appear on AMD's Phenom compatibility list. Asus has released a BIOS intended to support the Phenom, and for me, it worked like a charm. Interestingly, Asus did not include the TLB workaround in the version of the BIOS that I used. Also, for what it's worth, this Socket AM2 board ran the Phenom 9600's north bridge clock at 1.8GHz—just the same as on the AM2+ boards I've used.

The Asus M2N32-SLI Deluxe handled a Phenom just fine

Even more interestingly, although this wasn't the case with our M2N32-SLI Deluxe, I understand Phenom support is a bit of a tricky affair in some Socket AM2 boards due to BIOS ROM size constraints. On some boards, Phenom support is possible, but the procedure for upgrading is to flash to a Phenom-compatible BIOS using an Athlon 64, shut down, and then install the Phenom. If you want to go back to the Athlon 64, you must first flash to an Athlon-compatible BIOS using the Phenom. Personally, I could probably live with that, but I have ready access to spare chips to swap in. Without that, this limitation really does raise the degree of difficulty for a CPU swap.