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Topic Title: [Athlon FX] does it work in SMP-mode?
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Created On: 10/08/2003 04:24 PM
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 10/08/2003 04:24 PM
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odysseus
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Now I know that the Athlon FX isn't supposed to be used in SMP-systems - it is in fact more or less an Opteron 1xx. But I can't find anyone who has actually tried to run two AFXs (or Opteron 1xxs) in a dual-configuration. I've been going through the whitepapers and it says that the pins for the second and third HTT-link are not connected on the AFX - but whether that's the truth, I don't know. They might as well be connected to the internal HTT-links. It wouldn't be the first time something like that happens - think of the cache that can be enabled on Applebred/Thorton.

There are two possible problems: first, the motherboards can read the SMP-capabilities from the processor (there're two bits reserved for that, as I saw in the docs) and refuse to work when they detect a non-SMP-capable CPU. The second problem is of course the HTT-link, which could very well be disconnected or at the very least not be tested to work. It seems to me, however, that there's a reasonable chance to get this to work and it's worth trying at the very least.

For what it's worth, I've been searching on the forums of tweakers.net, 2CPU.com and AnandTech to find someone who tried it, but all I found was someone planning to test it in the coming weeks. If it doesn't work, I'm interested in the reason: it might for example be possible to get it to work by using a hacked BIOS, if the problem is around there.
 10/08/2003 04:30 PM
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ALIEN3001
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QUOTE think of the cache that can be enabled on Applebred/Thorton.

Look at the Athlon64 "nude" ( ) pictures, you'll se there's no bridges.

Now what?

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 10/08/2003 04:35 PM
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odysseus
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I know that it doesn't show any bridges - but I wouldn't expect to enable HTT-links by cutting or connecting bridges, even if I wouln't mind it if it was possible. It could very well be a BIOS-issue., or maybe there's some other way to get around SMP-disabling security measures.
 10/08/2003 05:20 PM
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ZapWizard
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It may be true that the Athlon 64 FX still contains two extra HT links.

But that would most likly only be on the die, not the pins.
If you look here:
http://www.amd.com/us-en/Proce...chni...39_7203,00.html' ">http://www.amd.com/us-en/Proce...0_182_739_7203,00.html

At the AMD Athlon 64 FX Processor Data Sheet it lists all the pins.
Mabye you can find some extra HT links listed in there.

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 10/08/2003 05:40 PM
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odysseus
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I've been going through the docs already. The pins that are used for HTT-link 2 and 3 are said to be 'not connected' on the Athlon FX. Beside that, there's a pin for PRESENCE_DET on the Opteron that's just connected to the ground on the AFX. However, the docs make clear that PRESENCE_DET is also internally connected to the ground - so no difference there. The only real difference that I can find that could be important: the two (read only, of course) bits that indicate whether a processor is capable of running in a 2-way or 4/8-way environment. I suppose that the AFX doesn't have any of those bits set, but I don't know for sure whether current BIOSs test those bits. Even if they do, they could be hacked not to do so, or one might think about other ways of solving that problem.
 10/09/2003 05:20 PM
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2002CBR600F4i
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I'd suspect the reason nobody has tried yet is because so few people have the needed hardware... There are very few FX-51's out in the wild, and even fewer people have access to dual Opteron MB's.

I'm surprised that the major sites like Anand and Ace's haven't been able to try it yet.

Honestly, I wouldn't be surprised if the FX51's are actually Opteron 24x's. Think about it... Which model Opteron does AMD always seem to release the new speed increase for first? The 24x Series. The Fx51 run's at 2.2Ghz (200Mhz faster than the 246).

Seems like AMD's primary Opteron production is for the 24x series, so if they're going to yank from anything, it's going to be that line to produce the FX51's.

Now, whether they will actually WORK as duals, who knows? Somebody will try it sooner or later...

--Mike


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Main Rig: 4800+X2 (AM2), Asus M2N32-SLI Deluxe Wireless, 4GB Corsair DDR2-800 CAS4 EPP, dual XFX 7900GT Extreme, 4 Seagate 300GB 7200.9 SATA2 drives (RAID5), 16X Sony DVD-ROM, NEC 3540A DVD-RW, Seasonic S12 600W PSU, Thermaltake Armor Tower case, Dell 2405 FPW.

File Server/Backup Rig: Athlon 64 FX-51, Asus SK8N, 1 GB Kingston HyperX memory, GeForce2GTS 64MB, 200 GB Maxtor HD, 40 GB Maxtor HD, 20 GB Maxtor HD, 48X CD-ROM, ThermalTake Xaser III case w/ Silent Purepower 430W

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 10/09/2003 05:27 PM
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Java
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I think the point that is being missed here is that it does not matter if the FX has the HT links or not. Yes it is similar to the Opteron 1xx, however the Opteron 1xx will not work in SMP mode either and it too has the HTT links.

So what enables SMP operation? The HTT links. If the Opteron 1xx has HTT links, then why won't it work in SMP mode? The links are not Coherent links. This is the key folks. HT has 2 modes of operation coherent and non-coherent. In order for 1 CPU to be able to talk to another, it needs to have a coherent HTT link and this what is different between a 1xx operton and a 2xx opteron. The same is true between a 2xx opteron and a 8xx opteron...more coherent HT links.

So the end result is don't even bother trying to run a FX or an 1xx opteron in SMP mode, it will not work.



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The opinions expressed above do not represent those of Advanced Micro Devices or any of their affiliates.

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