AMD A8-3850 APU Review: Llano Hits the Desktop

Author: MAC
Date: June 29, 2011
Product Name: AMD A8-3850
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The Effect of Memory Bandwidth on IGP Performance

Since Llano’s Sumo graphics controller is literally tied at the hip to the system memory through the 29.8 GB/s Radeon Memory Bus, it goes without saying that DDR3 DRAM speeds, capacity and timings will affect performance. Indeed, you’ll likely see every major DRAM manufacturer release some form of 2x2GB or more likely a 2x4GB Lynx platform certified memory kit in the coming weeks. But how much can your choice in memory impact in-game framerates and overall 3D performance? That’s what this section is all about, folks.

This bears repeating for anyone who skipped to this section: every A75 and A55 motherboard should have a setting within the BIOS which allows for the selection of preset frame buffer sizes along with an Auto default. Each step reserves an increasingly large chunk of the system memory explicitly for UMA (IGP) use and the Auto setting determines a frame buffer size based off of the amount of installed memory (usually a quarter of the system RAM will be reserved in this case).

The results as seen above are pretty straightforward. The 32MB and 64MB settings just don’t set aside enough memory and which results in the GPU being absolutely starved for bandwidth. Even the 128MB settings returns unacceptable performance levels, particularly at 1920 x 1080. At 256MB, things start to look much better but the minimum framerates suffer when the resolution is increased past the 720P mark. Both 512MB and 1GB seem to be the sweet spots for this game (and others we tested) as they both returned playable framerates at 720P but higher resolutions proved to be a bridge too far for the underlying GPU architecture.

Things started to get particularly interesting when setting aside a whopping 2GB of system memory for the GPU’s use. Our average results saw very little impact but even at 720P, this game chugged along in certain parts of the test race. In addition to the Windows 7 page file, our 4GB equipped system only had about 360MB of memory left for the CPU cores to utilize which led to processor bottlenecking and very low minimum framerates. To make matters even worse, the 2GB of memory is dedicated to the GPU at all times so Windows startup / shut down took far too long and even programs like Word, AutoCAD and Outlook were sluggish at best.

Boosting the onboard system memory to 8GB alleviated every one of the issues but judging from the performance we saw, the HD 6550D GPU just can’t take advantage of anything more than 1GB of memory anyways. Meanwhile, the Auto setting exhibited perfectly capable performance so we recommend sticking with the system defaults. Just be sure to check AMD's System Monitor to ensure the Auto setting is reserving the correct amount of memory.

Next up, memory speed and latency performance…

There’s no doubt about it: increasing memory speeds can have a drastic effect on performance but only up to 1600 MHz. Above that, tightening timings has a minimal affect at best and even between 1600 7-7-7 and 1866 6-6-6 there is very little improvement. This is likely due to the GPU’s inability to take advantage of higher memory speeds, particularly at higher resolutions. But if you are playing on a sub-1080P screen, a bit of extra performance can be found with ultra high memory speeds and tight timings. One thing that you will most likely want to avoid is a speed of 1066 which is ironically what most motherboards will read as the default SPD speed.

However, memory speeds can be a double edged sword as well. There are a small number of DDR3 kits that can effectively hit 1866 at CL6 and the few that do tend to carry a hefty price premium since their ICs are binned for overclocking. They’re usually so expensive that you’d be better off investing in less expensive memory and buying a dedicated entry level GPU like the AMD HD 6570 rather than trying to squeeze every last drop of performance from the IGP.

In our opinion, this is one of the few cases where faster isn’t better. For a perfect mix of performance and pricing, we’d recommend picking up a 4GB kit of 1600 MHz DDR3 which has the ability to hit CL7 at a reasonable voltage setting. Anything above that would be money wasted but remember to high tail it into the BIOS as soon as possible and change the memory speed since every modules we’ve tested (even ones certified by AMD) defaulted to 1066 MHz.

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