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AMD A8-3850 and A6-3650: staking it on the APU
by Guillaume Louel
Published on August 28, 2011

The platform

The desktop version of the AMD Llano platform is called Lynx. It of course brings together the APUs with new motherboards and a new chipset (southbridge).

Only two processor models have as yet been launched, the A8-3850 and the A6-3650. They both have a TDP of 100 watts.

Note the absence of Turbo mode, reserved for the A8-3800 and A6-3600 versions with a TDP of 65 watts, which have been announced but which aren’t yet available.

Placing a graphics chip in the processor requires a new socket, something AMD has had to reconcile itself to. Named the FM1, it has 905 pins and can be fairly easily distinguished by the square hole in the middle of the socket, where there are no pins, which is reminiscent of older sockets. From a physical point of view, the processors are identical in size and AM3 heatsinks are still perfectly compatible with FM1, as the fixture system is the same.

Two southbridge type chipsets are available for the platform, the A75 and A55. There are two notable differences between these versions, the A75 having 6 x 6Gbps Serial ATA ports (6 x 3Gbps ports for the A55) as well as 4 native USB 3.0 ports and 10 USB 2.0 ports (against 14 USB 2.0 ports for the A55). A bus AMD calls the UMI serves as the interface between the processor and the chipset. In practice this is a PCI Express 2.0 4x link, with the same method also used by Intel for its Sandy Bridge platforms.

AMD supplied us with an Asrock A75-Pro4 motherboard for our tests and we used it for most of the testing. Asus also sent us an F1A75-V PRO a bit later and this is what we used for the overclocking tests. Note that the BIOS' were particularly capricious on these cards, particularly when it comes to USBs. We experienced problems with the 3.0 ports in getting them to recognise USB keys and external hard drives, as well as keyboard problems. And this wasn’t all…

Dual Graphics: the return of Hybrid Crossfire

AMD has brought Hybrid Crossfire back in with the release of the A-series APUs. In contrast to the traditional version which doesn’t allow you to combine identical GPUs (if necessary the driver cuts down the clocks of cards with a common GPU and different clocks, for example the Radeon HD 5850 and HD 5870 in CrossFire are set up as 2x HD 5850s), Hybrid Crossfire does allow you to combine different GPUs with differing performance. This mainly concerns entry level cards as the option was originally introduced for ATI graphics chipsets combined with a discrete entry level graphics card.

This is now known as Dual Graphics. As we’ve already said, for marketing reasons OEMs that use Dual Graphics may give the name of a different virtual card to highlight the fact that they’re using such a combination. This table summarizes the combinations on offer for desktop APUs.

Note that these names are given for purely marketing purposes as in practice, both GPUs (the 6550D from the A8-3850 and the discrete graphics card) appear in Windows. In games, the name of the graphics card that appears (and its deviceId) will be that of the card to which you have connected the screen.

This is the other issue that we remarked on in the BIOS with this platform. Ideally, for maximum efficiency in Hybrid Crossfire, you plug the screen into the graphics card. Unfortunately, things aren’t as simple as this with current BIOS’. You have to activate dual graphics mode in the BIOS and then, only the motherboard video out is functional when you start the system up. The procedure recommended by AMD to activate Dual Graphics is as follows:

  • Plug the screen into the motherboard, activate Dual Graphics in the BIOS
  • Install the drivers in Windows and turn on Crossfire
  • Reboot, turn Crossfire off, turn off the system
  • Plug the screen into the graphics card, boot Windows blind (the screen only comes on when Windows has started)
  • Turn on Crossfire, reboot (still blind, for access to the BIOS you have to plug the screen into the motherboard again). Finally the machine is ready.

AMD says, thankfully, that it’s working to simplify the process and, most importantly, allow you to plug the video out into the graphics card when you boot in Dual Graphics mode. As things stand, OEMs which sell such machines cannot decently advise you to plug the screen in anywhere else than the motherboard. We measured the difference in performance between a Radeon HD 6670, and an HD 6550D + HD 6670 pairing plugged into the motherboard and then the graphics card:

Hold the mouse over the graph to view results at 1280x720

For now we won’t go into the fact that Dual Graphics can be slower than a graphics card on its own. We'll come back to this. In practice, the difference can be quite a big: you get a gain of over 26% in FarCry 2 at 1920x1080 when you use the ‘right’ out.

Test configurations

We carried out two distinct series of tests to measure, firstly, processor performance with an additional graphics card, and then graphics performance. We used the following platforms:

  • AM3: Gigabyte GA-890GPA-UD3H
  • FM1: Asrock A75-Pro4
  • 1155: Asus P8Z68-V Pro
  • Nvidia GeForce GTX 480
  • Western Digital Velociraptor WD3000HLFS 300 GB hard drive
  • 2 x 4 GB DDR3 G.Skill 2133 MHz (at 1600 MHz CL9)
  • Windows 7 64-bit

We installed the latest graphics drivers, a beta 11.6 version was supplied by AMD for Llano and we used it for all the AMD GPUs.

We tested the Intel Core i3 2100 and Core i3 2120 which are priced above and below the new AMD arrival (110 and 130 euros respectively). On the AMD side, for comparison, we added the Athlon II X4 635 clocked at 2.9 GHz. This processor is no longer on sale, but its spec is very close to that of the A8-3850 (clock, no L3, architecture) and gives us an interesting comparison. The current AMD offer in this price range takes the form of the Phenom IIs, with the 955, 965 and 975, costing around 100, 125 and 150 euros.

On the graphics side we tested, other than Llano performance, various entry level graphics solutions from AMD, namely the Radeon HD 5450, 6570 and 6670, the last two alone and in Dual Graphics mode. We also added the 890 GX (the current graphics chipset used with AM3) as well as the Intel HD 2000 and HD 3000 graphics cores, tested using the Core i3 2100 and 2105. We also added a Radeon HD 5570 clocked at the frequencies of the HD 6550D (600/800), so as to measure the impact of integration.

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