AMD A series won our hearts earlier this summer when it launched with a very powerful integrated graphics processor and a very competitive price. Some of the few drawbacks we could find was a disappointing overclocking experience. During the last few weeks we could conclude that the problems are bigger that we though, where both USB 3.0 and AHCI are affected.
We have been tearing our hair with a major comparison of AMD A75-based motherboards. We have posted shorter updates on Facebook, so it is no secret this has been anything but easy. The big problem has been our overclocking tets where have been stuck in discussions with manufacturers to try and get any overclocking results worth mentioning.
After several days of searching for errors it turns out that the biggest limitation of the AMD A75 chipset is its harddrive settings. Since the entry of the SSDs the AHCI setting with its support for NCQ, hot-swap and various energy saving functions been a given. This is also the setting we recommend that AMD A75 users isntalls and runs with. We have also been cursing quietly over all motherboars manufacturers ship their A75 motherboards with the IDE mode active from factory, which we now know why.
AMD A75 chipset is not perfect
AMD A75 is simply allergic to AHCI mode when overclocking. We have had big problems moving past 107 MHz bus speed with the storage unit in AHCI mode. Vi har We have tested both SSD and HDD and the problems are the same, and we hit the same FSB wall with nearly all motherboards. The exception is the Gigabyte board we used in our review of AMD Llano. This board namely automatically switches back to IDE mode when overclocking, even if we set it to AHCI in BIOS, which was why we didn’t discover this problem sooner.
Performance loss, at least with SSDs
We have been in contact with the manufacturers of several of the motherboards and they have told us that the IDE mode does not affect performance on the AMD A75 platform, but according our quick lab tests this is not entirely true. In PCMark7 performance improved 10% with AHCI turned on, and overall 4-6% better in the total score, compared to IDE at stock frequency (Corsair Force 2 120GB SSD).
Overclocking on AMD A75 is possible, but without IDE mode you will get nowhere
This makes overclocking on AMD A75 an uncertain bet and currently we a have hard time recommending it for a die hard fan, but sadly the problems doesn’t stop there.
The case of the lost USB performance
After a tip from our colleague Lars-Göran Nilsson, freelancing Swede in Taiwan, we started investigating the USB controller of the AMD A75 chipset when overclocking. AMD A75 is the first chipset on the market sporting an integrated USB 3.0 controller, and sadly there are some teething problems.
When overclocking, even with just a few MHz the integrated USB controller switches to USB 2.0 mode and drops all extra performance we would expect from our external USB 3.0 units.
USB 3.0 ports turns into USB 2.0 ports when overclocking
We have tried to reach AMD about these problems and hopes to return with more information. Why this happens and not the least, if and how do we solve this.
AMD A series and Llano is fortunately not intended for overclockers, but there are still two big drawbacks where overclockers will have to prepare to lose storage performance and functionality when overclocking. But perhaps the worst, losing the entire USB 3.0 interface, could render units incompatible. Some positive news is that external USB 3.0 controller circuits that are found on several of the motherboards are not affected. These still have full speed when overclocking, but the priamry that are controlled by the AMD A75 chipset gear down to USB 2.0.
On the whole Llano and Socket FM1 platform is still a very good platform for its target buyer, OEM and John Doe, but some of these teething problems (we hope!) is something AMD has to look over to make it attractive to enthusiasts.
We will return with more information when we have it.
Darn, thats problematic since it affects the PC configuration I was aiming for. However, what about underclocking in phases one needs to work on his termpaper and wants to dodge the electricity bill ?