AM3 Motherboards/Overclocking

To test out the performance of their new AM3 processors, AMD sent us two CPUs from today’s launch: the Phenom II X4 810, and the triple-core Phenom II X3 720 Black Edition. The 810 is targeted towards the user who needs four processing cores but doesn’t want to pony up the cash for a 910 or 920 CPU, while the X3 720 is obviously positioned towards users who don’t necessarily need four cores and want to save even more money.

AM3 Phenom II (left) AM2+ Phenom II (right)

Bottom of AM3 CPU (left) bottom of AM2+ CPU (right)

Physically the new AM3 CPUs look similar to their AM2+ counterparts, although obviously the new AM3 parts have two fewer pins on the underside of the processor. Since AMD hasn’t moved to pin-less packaging for their desktop processors just yet, fewer pins is obviously a good thing. The backward compatibility also makes it easier for do-it-yourselfers who picked up a 790GX or 790FX motherboard with AMD’s newer SB750 South Bridge last year who wish to upgrade to AMD’s latest processors.

Not everyone has an AM2+ motherboard though, or perhaps you want to squeeze every ounce of performance out of your AM3 CPU and wish to upgrade to faster DDR3 memory. For these users, you’ll want to upgrade to the latest AM3 motherboard and DDR3-1333 (or better) memory.

AM3 Motherboards

So far ASUS, Gigabyte, and MSI have announced AM3 motherboards, with all three manufacturers offering multiple AM3 options. ASUS has announced the most AM3 SKUs to date, with their M4A78 and M4A79 series comprising of four motherboards. The M4A79T Deluxe is AMD’s flagship offering and is based on AMD’s 790FX+SB750 combo, while the M4A79 Deluxe supports DDR2 memory. For integrated platforms ASUS offers the M4A78 Pro, which is based on AMD’s 780G chipset. Finally, the M4A78-E utilizes 790GX.

Like the M4A79T, Gigabyte’s GA-MA790FXT-UD5P is built around AMD’s 790FX chipset with SB750 South Bridge, and offers multiple DDR3 speeds beyond 1333MHz. The GA-MA790XT-UD4P is the first 790X motherboard to support AM3, with support for CrossFireX and hopefully lower pricing than 790GX motherboards.

Finally there’s MSI. MSI’s also announced two AM3 motherboards. The 790FX-GD70 is their 790FX+SB750 offering for enthusiasts. DDR3 speeds up to 2133MHz are available within the board’s BIOS. For mainstream users MSI offers the 790GX-G65, which relies on AMD’s 790GX chipset with DDR3 speeds topping out at 1600MHz.

For the sake of our sanity, we’re holding off on AM3 motherboard testing until the motherboard manufacturers have had more time to fine tune their BIOS’ for the new AM3 CPUs and DDR3 memory. Even existing AM2+ boards have had some last minute BIOS adjustments for AM3 CPUs, so rather than troubleshoot issues with AM3 boards, we’ve decided to play it safe and stick with just AM2+ testing for now.

For the record, AMD has stated that DDR3-1333 should improve performance by up to 5% under the right conditions.

Overclocking

With AMD baking in enhancements into their new 45-nm manufacturing process, we were eager to see how far we could push our latest Phenom II CPUs utilizing the AM3 socket. With its unlocked clock multiplier and one fewer core, we were particularly curious to see how far we could push the Phenom II X3 720 Black Edition. It didn’t disappoint.

At stock voltage levels, we were able to hit speeds of 3.03GHz, with the multiplier at 13.0x and the HT link speed of 233.6.

With the voltage cranked up to the max of 1.55V, we were able to hit speeds of 3.8GHz. That’s actually slightly higher than the 3.745GHz we hit with our Phenom II X4 940 sample a month ago.

Phenom II X3 720 Stock

Phenom II X3 720 Overclocked

We could actually boot up some apps at even higher speeds, but couldn’t maintain stability. Windows Vista would BSOD at the splash screen at 4GHz.

We didn’t manage to have the same luck with our Phenom II X4 810 sample, but it wasn’t due to the fault of the CPU itself, rather we’re chalking it up to a software issue. Unfortunately for whatever reason AMD’s Overdrive tool wouldn’t allow us to crank up the CPU voltage beyond 1.325V, and when we attempted to dial in higher voltages manually via the BIOS of our motherboard (an ASUS M3A78-T), the motherboard failed to POST. Even if we cranked the HT link speed up just 5MHz with higher voltage. In fact, our Western Digital hard drive would make a clicking noise as if it were about to fail.

So armed with no way to adjust voltage, our X4 810 maxed out at 3.1GHz. That’s actually a little higher than the speed we hit with the X3 720 at stock volts, and it’s also a 500MHz OC, but we can’t help but wonder what kind of potential is lying untapped in this particular sample. 3.9GHz perhaps? While it had no problems with the X3 720 BE, the ASUS BIOS is likely having problems picking up the 810.

Phenom II X4 810 Stock

X4 810 Overclocked

Overdrive maxes X4 810 voltage at 1.325V

Besides the AM3 processor and ASUS M3A78-T mobo, we also used Zalman’s all-copper CNPS 9700-Cu CPU cooler along with Antec Formula 5 silver paste, OCZ Platinum RAM and Windows Vista Ultimate 64-bit. Keep in mind that 32-bit operating systems tend to OC further than 64-bit.