Turn A Phenom II X3 Into An X4
Back on Feb. 9, AMD launched a handful of AM3 Phenom II processors built using the firm’s latest 45nm manufacturing process. We came away from our initial testing satisfied that AMD had a real winner on its hands in both the Phenom II X3 and X4 processors. The new CPUs launched at higher initial clocks than their predecessors and also exhibited significantly more overclocking headroom. Add the multiplier-unlocked Black Edition models and prices that put the squeeze on some of Intel’s midrange offerings, and you have all the makings for a successful product. But two weeks later, the Korean hardware site Playwares (www.playwares.com) discovered a somewhat obscure BIOS setting available on some AMD chipset motherboards that, when set to Auto, would turn select tri-core Phenom II processors into fully operational quad-cores. As the news filtered through the enthusiast community, others began reporting success with certain motherboards and processors while sales of AMD’s Phenom II processors started to take off. DigiTimes (www.digitimes.com) reported high demand for AMD’s new Phenoms, and motherboard makers claimed AMD could earn up to a 30% share of the global desktop CPU market in Q2 (up from a previous 20%). There’s no data to show a direct correlation, but the exploit couldn’t have hurt the Phenom II’s popularity. We contacted AMD to get its take. Product Manager Damon Muzny responds,“We’re quite excited by the attention and interest folks are showing in the new 45nm Phenom II processors, especially for our Black Edition X3s and X4s.” And AMD should be proud of its Phenom IIs. But if there’s a chance of getting a quad-core Phenom II for $145 or $125, well, that’s just icing on the cake. Read on as we cut through the speculation and attempt to unlock a Phenom II X3 and show you what it takes to do it yourself.
Quad-Core Caveat Emptor
This is the part of the show where we tell you that although it’s possible for you to replicate our successes (more on those later), it’s also more than likely that you’ll replicate our failures (more on this, too). Every three-core processor has four cores, but the disabled core presumably didn’t pass validation testing and was disabled for that reason. Even if you manage to unlock this core, it may be unstable, negatively impact your system performance, and could cause your system to become unbootable. Should you be one of the lucky few who manages to get a fully functioning quad-core CPU from your Phenom II X3, it will draw significantly more than its rated 95W (expect closer to 125W under full load). Enabling the fourth core would likely also void your warranty and has the potential to shorten the life of your hardware. Having said that, let’s dig in.
The first thing you need is a Phenom II X3 processor, of which there are currently two: the 2.6GHz Phenom II X3 710 and the 2.8GHz Phenom II X3 720 Black Edition. We had a 720 in house that AMD sent us for the initial launch of the series, but we asked the firm to send us a 710, as well. But not just any old Phenom II X3 will do. According to the information we’ve been able to uncover, only 720 and 710 processors from batches manufactured on certain dates have any success with the exploit. Playwares achieved its results using processors manufactured in the fourth week of 2009, while other sources claimed varying degrees of success with processors dated in the 46th and 51st weeks of 2008 and the fourth and sixth weeks of 2009. To determine if a given Phenom II X3 processor has a good chance of working with this exploit, you’ll need to look at the three rows of alphanumeric characters that make up the part number etched into the CPU’s heatspreader. Pay particular attention to the far right block of four numbers followed by four letters in the middle row. For our Phenom II X3 720, the number is 0849CPMW, while the 710’s number is 0906MPMW. The numbers refer to the week the die was manufactured. For instance, our 720 was manufactured in the 49th week of 2008, and the 710 was manufactured in the sixth week of 2009. Despite the fact that only the 710’s date batch had any reports of success, we resolved to try both processors. Regarding a motherboard, you will need one with the AMD 790FX or GX chipset, particularly one that features the SB750 Southbridge, and a BIOS that supports ACC (Advanced Clock Calibration), the feature that enables the system to recognize the fourth core of an X3 processor. At press time, a German site (www.hwbox.gr) also reported success using the Nvidia chipset-based Gigabyte GA-M720-US3 paired with a beta BIOS. Because the first site to report the exploit, Playwares, used the Biostar TA790GX 128M, we decided to use that motherboard as the platform for our testing.
Try, Try Again
Our system consists of the Phenom II X3 710 and 720, a Cooler Master V8 CPU cooler, Biostar TA790GX 128M (AMD 790GX + SB750) motherboard, 2GB Corsair TWIN2X2048-6400C4 (2x 1GB, DDR2-800) SDRAM, ATI Radeon HD 4890 graphics card, PC Power & Cooling Silencer 500 EPS12V power supply, and a 1TB Western Digital Caviar Black WD1001FALS hard drive. The Biostar motherboard’s BIOS is version 2.61, and Windows Vista Ultimate is our OS. We started with the higher-performing processor first, the 2.8GHz Phenom II 720 Black Edition. We installed it into the system, entered the BIOS Setup Utility, navigated to the Advanced tab, selected CPU Configuration, scrolled to the bottom of the page to highlight Advanced Clock Calibration, and set it to Auto. After saving the changes and restarting, the PC wouldn’t budge from a black screen, failing to boot or even begin the POST. We pressed CTRL-ALT-DELETE and tried to reboot, and again, the system failed to even initialize the display. This unsurprising result is likely to happen when you turn on ACC with most Phenom II X3s that aren’t from one of the magic batches. According to a product manager from a prominent motherboard manufacturer, “The original function of Advanced Clock Calibration is to sync the different speeds of each core of a multicore processor”— to help when overclocking the original Phenom processors. Prior to the launch of the Phenom IIs, and before the tech press discovered ACC’s special new ability, an AMD product manager had this to say about ACC: “Things learned through developing ACC with the 65nm Phenom were baked into our new 45nm Phenom II silicon. . . . You can just as well leave ACC off for Phenom II [overclocking] testing.” Our unnamed source tells us his theory as to why ACC unlocks the fourth core of Phenom II X3 processors. “These X3 cores are actually X4 cores, and . . . the ones that fail in certain cores, instead of throwing them away, [the chip maker] just disables [the core] with a register that they add in, and in certain date codes, [AMD’s] manufacturing plant failed to add that register.” Then presumably, stability concerns notwithstanding, this exploit should work on every processor from those certain date batches? “Yes. Actually, we’ve known about this for some time.” When pressed for when the ACC exploit first came to his attention, our contact explains, “I seem to remember seeing something about this in . . . November or December.” Armed with renewed confidence and one more Phenom II X3 processor to test, we cleared the CMOS, removed our stubborn Phenom II X3 720 Black Edition, installed the Phenom II X3 710, switched ACC to Auto, crossed our fingers, and restarted. Almost immediately, we were greeted with a positive sign, as the POST displayed our CPU as an “AMD Phenom II X4 10 Processor.” In Windows, a popup informed us that device driver software installed successfully for an “AMD Phenom II X4 10 Processor.” CPU-Z also confirmed that although we were running a Deneb-based Phenom II X3 710, it was equipped with four cores and capable of handling four threads. To determine if a heavy load would trip up our new quad-core, we ran Prime95 on all four cores for an extended period, and it breezed through with flying colors. We ran our suite of processor-stressing benchmarks, and the system remained stable throughout. Better than stable: In benchmarks that scale well between multiple cores, our unlocked Phenom II X3 710 was performing in line with what we’d expect from a quad-core Phenom II. Check out the “Unlocked & Overclocked” chart to see the numbers. Having proven that our Phenom II X3 710 can be unlocked to take advantage of its dormant fourth core, we decided to push our luck a bit and overclock it. Although we wanted to get as much performance out of the chip as possible, we were also wary of pushing the thermal envelope too much. We managed to get stable performance at 3.18GHz by tuning the CPU HyperTransport clock to 245MHz, increasing the northbridge frequency to 2,000MHz and giving the CPU an additional 0.125V to work with. As a result, our unlocked and overclocked Phenom II X3 710 outperformed AMD’s Phenom II X4 940 Black Edition (see page 43 in CPU’s March 2009 issue), a processor that—as we went to press—was selling for close to $100 more than the Phenom II X3 710.
Four Is Better Than Three
As hacks, mods, and exploits go, unlocking the fourth core on a Phenom II X3 processor is about as easy as it gets. Unfortunately, the hard part is just getting your hands on a processor from the batch missing the fourth core disable register. Unless you can find an online retailer that will reveal the batch numbers prior to purchase, there’s no way to know if you’re getting an X3 from an exploitable batch. On the other hand, our winning 710 is one of the more recent X3s to show success, so there’s a possibility that any X3 that has a stable fourth core will work.
Source of Information : CPU Magazine 07 2009
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