|AMD Athlon-II X4-640 CPU ADX640WFGMBOX|
|Reviews - Featured Reviews: Processors|
|Written by Hank Tolman|
|Friday, 02 July 2010|
Page 11 of 13
AMD Athlon-II Overclocking
Now let's get into overclocking. Since the Athlon-II X4-640 is not a black edition CPU, I couldn't increase the multiplier to overclock it. Still, while the multiplier is stopped out at x15, it is important to note that it can still be decreased down as far as x4. Because of this, it is possible to decrease the multiplier and increase the bus speed and voltage and still maintain and stable overclock. To start off, however, I wanted to see how far I could get with the overclock of the Athlon-II X3-445 by just increasing the bus speed. Using the ASUS M4A785TD-M EVO, I started at 225MHz on the bus speed and increased by 5 until I couldn't boot into Windows. I was able to reach 250MHz before the Auto voltage setting didn't give me enough power to boot the system, but the overclock wasn't stable enough to withstand stressing. After increasing the voltage to 1.55V, I was able to get to 255MHz. This time it withstood the stressing like a champ, giving us our most stable overclock at 3.8GHz.
With the Athlon-II X4-640 at 3.8GHz, we achieved a 21% increase in core speed using just air to cool it. I tried getting even higher by dropping the multiplier down as far as x13.5 and increasing the bus speed above 300MHz, but I wasn't ever able to achieve a stable setting higher than the 4.1GHz I had already reached. All of my overclocking was done with air cooling only using the Scythe Mugen II CPU Cooler.
Before ending up at the 255MHz bus speed magic number, I was able to make it into windows and begin stressing the CPU at even higher speeds. Originally, I thought I had found a stable overclock as high as 3.99GHz with the bus speed set to 266MHz. Running the stressing procedure I mentioned above usually weeds out any unstable overclocks and I am able to perform testing after that. Even so, with the bus speed at 266MHz and the voltage at 1.54V, as you can see in the screenshot below, I got through all the stressing and was ready to start testing.
When I began the testing with the X4-640 at 3.99GHz, everything went fine. It wasn't until about halfway through the PCMark Vantage tests that I started having problems. The computer crashed at that point and restarted. I was a little confused by that, so I ran the stress testing procedures again. Within an hour, the overclocked failed stressing. I pushed up the voltage as high as 1.60V to see if that would help the CPU withstand stressing at the same high bus speed. It didn't work. At 3.99GHz, the processor could not again hold up to stressing. I moved the bus speed down 1MHz at a time until I ended up back at 255MHz and the processor once again withstood the stressing.
Even when using two different processors of the same make and model, or two of the same motherboard, they will likely result in different abilities as far as overclocking is concerned. While I was able to reach an overclock of 3.8GHz with air cooling, I highly encourage anyone to try out their own methods, especially with an entry-level quad-core CPU such as the X4-640. The mechanics of overclocking have more to do with the amount of voltage I can safely send to the CPU or through the northbridge. With the testing motherboard being an entry-level product itself, it doesn't have a MOSFET heat sinks or even that large of a heatsink on the northbridge. Overall, I was not disappointed by the overclock I was able to achieve at 3.8GHz. I hope you will all take the time to (carefully) test your own hardware to see how far you can safely stretch it. It certainly is a lot of fun.