AMD Motherboards: Processor Support

Everyone was pleased to hear that the new AMD Venice and San Diego processors would work fine in their Socket 939 motherboards. In many cases, however, a BIOS update is required to support these latest Revision E Athlon 64 chips, which are based on the 90nm manufacturing process and support SSE3 extensions.

Then Venice/San Diego got extended with the Dual-Core X2 processors. The good news is that, once again, any Socket 939 motherboard can theoretically support the new x2 processors with a BIOS upgrade. This was certainly a welcome contrast from the Intel dual-core announcement which required new chipsets and motherboards for dual-core to function. However, since the official launch of X2 at Computex earlier this month, confusion seems to reign as to which boards support Dual-Core processors.

To try to shed some light on the current BIOS revisions and processor compatibility we took a closer look at the state of x2 processor support among motherboards. In many ways the adoption of x2 is faster than we expected, but there are still gaping holes in x2 and Rev. E processor support. Hopefully with this guide and a little research you can find the perfect motherboard home for your new Revision E or x2 Dual-Core Athlon 64 processor.

The Processor Factor

Another concern has raised its head in the last few months that should be a consideration for anyone shopping for an Athlon 64 motherboard - the processor factor. When we tested the nForce4 SLI boards we used the 4000+ clawhammer chip as our standard CPU. We also had done some testing with the early Winchester chips which were based on the 90nm production process instead of the 130nm process used for clawhammer. Overall these early 90nm chips were mainly a die-shrink, and performance - and compatability - were much the same whether clawhammer, winchester, or newcastle.

Recently, however, we have some new choices from AMD in Revision E chips and dual-core. These new Revision E parts support SSE3, are based on the 90nm process, and they do not always behave as earlier chips did in the same motherboard. We saw this for ourselves in our Gold Editor's Choice MSI K8N Neo4/SLI. While we experienced outstanding overclocking with a clawhammer chip, users with Venice chips were experiencing perfectly miserable overclocking results. It has taken MSI some time to find a solution to this problem, but we are happy to report that a new BIOS has just been released that claims to fix the Venice issues on the MSI. The point of this is that the newest Athlon64 Revision E chips, code-named Venice and San Diego, do behave differently than earlier Athlon 64 chips in some boards. This is likely a temporary concern as the market adjusts to the newest CPU architectures, but it is a factor that should be considered.

This becomes an even larger issue with the new Toledo dual-core processors. The Athlon 64 X2 joins two Venice or San Diego cores on a single CPU. These Revision E X2 dual-core CPUs - the 4200+, 4400+. 4600+, and 4800+ - theoretically will work in any Socket 939 board. However, you will certainly need at least a BIOS upgrade. Most of the major manufacturers have quickly brought the needed BIOS upgrades to market, but if you plan to run a dual-core chip you need to check before you buy.

It should also be mentioned that AMD has implemented a hidden feature in Revision E processors, namely additional memory ratios that can be implemented in BIOS. We saw a Revision E chip mounted on the Abit Fatal1ty AN8 motherboard. Adding the new processor gave the additional options of 433, 466, and 500 to the available memory ratios. This has to be coded in the BIOS to be available, but the new asynchronous ratios are a feature of the Revision E Memory Controller.

The good news, unlike the Intel dual-core, is that just about any Socket 939 motherboard can run dual-core. But you will definitely need a BIOS update and you will definitely need to check to make sure the board you are looking at has an available BIOS supporting dual-core.

Updating DC BIOS & Revision E Memory

Updating BIOS for Dual Core with an x2 Processor

This brings up the nagging question that is always asked when BIOS upgrades are required for certain CPUs. What do you do if you have a board that needs a BIOS upgrade for dual-core and you only have a dual-core chip? We asked AMD this question and got the following reply:

"If the BIOS you are working with (original BIOS in the board) supports a rev E single core (AKA... 90nm as most new boards should), it will allow you to flash the BIOS to a BIOS that supports rev E dual core. In my experience, a DC processor with single core rev E support will run fine, but only as a single core. If the BIOS doesn't support rev E (In other words, you may have a good board, but the BIOS is pretty old), you will likely need to install a pre-rev E (AKA-130nm) AMD processor to flash the BIOS.

I'm told that if a customer can't flash their BIOS, many mobo vendors will mail out the BIOS chip to them (if it's not soldered down, obviously)"

Revision E Memory Controller PLUS 4 Dimms =

The memory timings, in the end, are controlled by the memory controller, and in the case of Athlon 64 that memory controller is on the processor. We had already been told by AMD that Rev. E would feature a new and improved memory controller. In fact for months prior to the release of the new Revision E Athlon 64 processors (Venice, San Diego, Toledo) we have been hearing that the new memory controller on the Rev. E chips would allow the use of 4 dimms at the faster 1T Command Rate.

With the 4200+ x2 in our DFI LANParty nForce4 SLI test bed with a working dual-core BIOS (6/23/05) we tried 4 matched PC3200 OCZ Platinum Rev. 2 dimms. Four double-sided (or double- bank) dimms STILL require a 2T command rate in this configuration, so the limitation stills remains. Four DS Dimms in a Rev. E still need a Command Rate of 2.

AMD Recommended Motherboards for Dual Core

The AMD website has extensive lists of tested and approved motherboards for Athlon 64 processors. A listing on the AMD site is Official support for a CPU as established in AMD testing. AMD's Official list of motherboards supporting x2 processors is pretty short.

Socket 939 Motherboards with Dual-Core BIOS

In addition to the Official X2 Support list from AMD, manufacturers are releasing x2 BIOS updates for their motherboards. Below is a list compiled from the manufacturers that claim x2 compatibility with their BIOS update.

In general a board must be Socket 939, and the x2 updates, at least for the present, are mainly limited to the nVidia nForce4 family and a few VIA K8T890/K8T800Pro motherboards. The new ULI 1689 chipset also features x2 support, with AGP 8X on the M1689 and PCIe with the M1695. There are also several older VIA AGP boards in the X2 support list. ATI Crossfire AMD and SiS 756 also support dual-core, so new motherboards using these chipsets will support the new X2 Athlon 64.

"Check Web Site" means we could not find BIOS support for x2 processors at the website, and that you need to check the website or contact the manufacturer for an updated support lisitng.

Dual-Core BIOS Revision is the earliest listed BIOS to support Dual-core. Later BIOS for the same board can reasonably be expected to also support x2 processors.

Final Words

The latest AMD Athlon 64 processors bring with them performance improvements, and a new round of potential compatibility issues. Venice, San Diego, and Toledo (x2) all have the 90nm manufacturing advantage and the addition of SSE3 instructions. While they will all potentially work on any Socket 939 board, all three new processors require a BIOS update, which may or may not be available for your favorite board.

In general, motherboards based on the nForce4, VIA K8T890, Uli1689, SiS 756, and ATI Crossfire AMD will likely already have a BIOS released that will work with x2 processors or one will be coming shortly. Those with motherboards based on the earlier nForce3 chipset may not be so lucky - as BIOS' that support x2 on nForce3 are just starting to appear. We are told nF3 support for x2 is coming, but it is definitely coming more slowly. This means most Socket 939 boards with AGP video may not be supported right now with an x2 BIOS upgrade. We say most, because the new ULi 1689 chipset does support both AGP and x2, and some of the older but popular VIA AGP boards have x2 BIOS updates available.

AMD has also added additional "hidden" features in the AMD on-processor memory controller. Additional asynchronous ratios are available at 433, 466, and 500 memory speed on boards that implement the necessary code to access these memory controller features. These options should be available with any Revision E chip if the manufacturer implements the controller option read in BIOS. We saw the additional options "magically" appear on an Abit AN8 Fatality motherboard when a 4200+ x2 processor was used.

Unfortunately the long-rumored 1T Command Rate with Rev. E AMD processors appears to have been just a rumor. We could not run 4 matched dimms at 1T in a motherboard with Rev. E/x2 support. Four dimms still required a 2T Command Rate.

You should consider our list of Official and Unofficial Dual-core support to be a unified Revision E list. AMD tells us that Revision E support is part of the requirement for x2, so you can assume any x2 capable board will also properly support Venice and San Diego.

Fortunately for those shopping for a new Socket 939 motherboard there are many new boards that support Revision E and x2 processors. We hope the information in the article will make your search for a new motherboard for an Athlon 64 an easier process. If we overlooked boards and/or BIOS revisions that belong in our Supported list please let us know.