Introduction to Phenom Overclocking

We take a couple of AMD Phenom 9600 Black Edition processors, fully unlocked out of the box, and try to overclock the hell out of them. We also take the new AMD Overdrive utility for a spin and see how it stands up for modern overclockers.

To say that there was an elevated level of excitement throughout the past year about the AMD Phenom is an understatement.  Users all over the world scrabbled for information on what was to be AMD’s latest and greatest foray into the processor world.  Unfortunately the reality did not quite live up to the hype.

AMD was expecting to launch the initial Phenoms at a maximum clockspeed of 3 GHz.  AMD had done a lot of internal changes to the base design to hopefully get the product to where it needed to go.  Each core was internally optimized to increase both IPC and overall clockspeed on AMD’s 65 nm SOI process.  AMD also has been working diligently to improve the quality of their 65 nm process so it could hopefully handle this large and complex quad core part.

Unfortunately for AMD, things didn’t work out as planned.  The design does not seem to give enough leeway to advance clock speeds to a high level consistently, plus we have the very popular TLB errata that has branded the Phenom as a “sorta broken part”.  Until recently, it seems as though AMD has had major issues getting its 65 nm process up to speed.  Only now are we starting to see 65 nm X2 parts that consistently can make it to 3 GHz and above at default voltage.

All is not lost at AMD though.  The errata really only rears its head in very particular circumstances, though primarily in virtualization applications.  Average users such as office productivity folks, gamers, and photo and video editing makers will likely never run into any issues derived from this erratum.  The company is still producing rev. B2 parts successfully, and has been able to get quite a few of them to market.  The Phenom 9500 and 9600 are priced at $199 and $239 respectively.  These are the most inexpensive quad cores on the market so far.  AMD has recently introduced the new Black Edition of the Phenom 9600.  This fully unlocked part promises good performance at its designated clockspeed, but AMD is hoping that enthusiasts will enjoy the freedom to easily overclock these chips and buy them by the truckload.

Today I am going to attempt to overclock not only the BBE 9600, but also the Phenom 9900 (2.6 GHz) engineering sample that AMD was kind enough to send out to me.

Phenom Overclocking Basics

When the original Athlon 64 was released, there was a lot of confusion about how best to overclock this particular processor.  Many people were not aware of how sensitive the initial chipsets were to setting higher HyperTransport speeds, or how memory scaled with increases or decreases in the core processor speed.  Eventually people figured out that turning down the HyperTransport divisor, as well as decreasing the memory speed allowed the Athlon 64 to stretch its legs.

We are now hitting that same area with the new Phenom.  People were expecting to hit high HyperTransport speeds with the release of the new HT 3.0 specification, and the availability of highly overclockabled (and cheap) DDR-2 memory would make overclocking the Phenom a breeze.  This was unfortunately not true.  Most Phenom processors and motherboards are crapping out when HT speeds reach around 212 MHz, with the most aggressive overclocks by professionals hitting 220 MHz.  This is a far cry from the 330 MHz+ overclocks that the older Athlon X2s are able to hit (and higher when using these HT 2.0 parts with the new 790FX chipset).

Right now the best possible way to easily overclock a Phenom is to get an unlocked multiplier edition, and that means paying for the Black Phenom 9600.  Luckily for users, the price of the BBE is the same as the standard Phenom 9600.  The two differences between the products are that the retail product has a fan and heatsink and is multiplier locked (obviously).  So if an enthusiast wants to see how far his chip will go, then the BBE will be a must.

The 2.2 GHz and 2.3 GHz Phenom parts are both listed as 95 watt units.  The upcoming 2.4 GHz part is listed at 125 watts.  This is a pretty hefty jump for 100 MHz, but from what I am seeing from my little perch… it is likely correct.  These chips get toasty fast once they get past 2.3 GHz.

AMD Phenom 9600 Black Edition Review and Overclocking Test - Processors 12
Phenom 9900 Engineering sample on left, 9600 Black Edition on right

When AMD was designing the Phenom, they chose to implement multiple clock domains, so some of the parts internally run faster or slower than others.  There is a bit of confusion about how AMD was to implement this, as there were expectations that the “northbridge” functions (in this case the memory controller and L3 cache) would be able to run faster than the CPU cores, and they had their own separate power plane to draw from.  Things did not work out in this situation.  The northbridge part of the chip is actually running significantly slower than the CPU cores, and this is having a small effect on performance.  The 2.2 GHz and 2.3 GHz parts have the northbridge running at 1.8 GHz, while the engineering sample 2.6 GHz part has the northbridge running at 2.0 GHz.  This is not necessarily surprising since the memory controller was one of the bigger power hogs in the older Athlon 64 derivatives.

The split power plane is a good idea though, and it is better able to meet the growing power needs of these complex CPUs.  It also allows a lot more granularity in controlling power consumption where power is the primary concern.  Every AM2+ board out there now features a full 4 phase power delivery system, which should help smooth out any power ripples to these new processors.  Theoretically this split plane design should help out overclocking as well.

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