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Odd Dell Problem - RAMBUS and FSB:DRAM Timings

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Odd Dell Problem - RAMBUS and FSB:DRAM Timings

Postby Ian on Mon Nov 01, 2004 2:51 pm

Here at work, we've been working with Dell to fix an odd problem we're seeing on some of our computers. To give you a little background, we ordered a bunch of 1.8GHz Precision 340's in the spring of 2002. When we opened a new building in the fall of 2002, we bought another 70+ Precisions to fill it. The only difference is that they had 2.4GHz P4's. Oddly enough the older 1.8GHz machines work fine.. the problem is with the ones with 2.4GHz CPU's.

The problem is that we're seeing decreased network performance when run at 100 full (they have on board 3com 920's) When launching a program over the network, it normally would take say 40 seconds to launch. On these computers it takes 3-30 minutes. As a short term solution, we've manually set the NIC's to 10 full.

For the heck of it, I took the CPU and memory from a 1.8GHz machine and put it in a 2.4GHz. Surprisingly the problem went away. After doing some poking around, I realized that while the memory is running at 400MHz on both machines, the CPU's Dell put in the 2.4GHz ones ran at 533MHz and the FSB:DRAM timings were 4:3.

My question to all of you: Does anyone know if there are any issues with the Intel 850/850E chipset and running your CPU and memory at different timings? I know there were some PCI latency problems with some early P4 chipsets and PCI video cards, but I have not found anything that would explain the problems I'm seeing. Thoughts?
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Postby LoneWolf on Mon Nov 01, 2004 5:27 pm

I don't remember anything about this, but I do recall something about a 3com driver issue at one point where the negotiation wasn't working right (3com had to issue an updated driver, which they have done). Are all systems the same 3com driver revision?
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Postby Ian on Mon Nov 01, 2004 6:10 pm

LoneWolf wrote:Are all systems the same 3com driver revision?


Yeah, I've tried about 6 different driver revisions, including the latest beta from 2003. We've also tried various switches and switch configs.
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Postby LoneWolf on Tue Nov 02, 2004 10:02 am

Just for fun, have you tried a PCI NIC card, say an Intel 8255x of some sort? I'd be interested in narrowing down not only whether it's the 3com chip, as well as in what way the issue might be tied to the system bus.
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Postby Ian on Tue Nov 09, 2004 5:31 pm

LoneWolf wrote:Just for fun, have you tried a PCI NIC card, say an Intel 8255x of some sort? I'd be interested in narrowing down not only whether it's the 3com chip, as well as in what way the issue might be tied to the system bus.


Sorry for the lack of replies.. been busy with other stuff at work. Yeah, we tried an Intel PCI NIC. While a coworking initially thought this fixed the problem, I ran some more tests and found that it really didn't.

Dell did send us a 2.4GHz CPU with a 400 FSB and it works perfectly. Hopefully they can dig up another 70 of them. :D
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Postby LoneWolf on Fri Nov 12, 2004 12:25 pm

That's really funky. Don't know what else I can say. I'd guess there's some wierd clocksync problem on the mainboard, possibly even a hardware bug.

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Postby Ian on Fri Nov 12, 2004 1:30 pm

It's very sporadic too. Sometimes it will work.. and then later it won't. The only way to fix it 100% is to replace the CPU.
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Postby pranav81 on Mon Nov 15, 2004 2:44 am

Cant you change the timings in BIOS?


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