Several years ago I got two Supermicro X7DBE boards at a bargain price. These are nice dual Socket 771 boards of circa 2007 vintage, built around the Intel 5000P Blackford chipset and using FB-DIMMs with up to 32GB memory supported.
Recently I pulled one of the boards out of storage and installed two quad-core Harpertown Xeon E5450 processors in it, primarily for the purpose of verifying that newly arrived FB-DIMMs work. The memory worked just fine… but something else didn’t.
The CPUs ran at only 1.2 GHz (instead of 3.0 GHz), and even worse, one of the CPUs was not recognized. I swapped the CPUs around but that didn’t change anything—one was still not recognized. I plugged in two slightly slower Xeon E5430 CPUs… and one still wasn’t recognized, and instead of 2.66 GHz the CPUs ran at 1.06 GHz. I thought the board perhaps got damaged during moving and didn’t investigate further.
Sometime later I pulled out the other X7DBE board. It had two E5430 Xeons installed already. When I first tried it, both CPUs were recognized, running at 2.66 GHz as they should. Board clearly working.
So I thought, let’s put the faster E5450s in it. I did… and one of them wasn’t recognized, while the other ran at 1.2 GHz! I put the original E5430s back, but oops, one wasn’t recognized and the other ran at 1.06 GHz.
Okay, this is really weird. In desperation, I put in two Dempsey 5080 Xeons, the latest and greatest (if such a thing can be said) NetBurst Xeons. And again, one of them was not recognized, although the other at least ran at the full 3.73 GHz. Hmm…
For good measure I also tried two dual-core Woodcrest 5110 Xeons, but it was just more of the same. Only one CPU recognized, running at 800 MHz instead of 1.6 GHz. I tried all I could think of—resetting the CMOS (more than once), tweaking various BIOS settings, but nothing helped. Besides memory, the board was stripped to the bare minimum—onboard video and keyboard, nothing else. Nothing made any difference.
As always, this sort of problem has been seen before, with no resolution.
A few days later I ran additional tests. First of all I tried a different PSU, but that made absolutely no difference. I should note that the PSU I mostly used with the X7DBE boards has no trouble powering a dual Opteron board.
Next I did a bit of math to figure out the strange frequencies. The result was pretty clear: The CPUs run using the proper multiplier but with a 133 MHz BCLK (which is technically not even supported by these CPUs at all!). Thus a 3.0 GHz CPU which normally runs with a 333 MHz BCLK and 9.0 multiplier becomes a 1.2 GHz CPU with 133 MHz BCLK and the same multiplier. A 2.66 GHz CPU is the same thing only with an 8.0 multiplier, and becomes a 1.06 GHz processor with 133 MHz BCLK. In the last example, a 1.6 GHz Xeon 5110 normally uses a 266 MHz BCLK and a 6.0 multiplier, therefore dropping to exactly half the speed with 133 MHz BCLK.
Okay, so maybe the board has trouble reading the CPU signals identifying the desired BCLK frequency. I looked up which pins are used for that and carefully checked all four sockets (two on each board). But I found no problems, all pins were straight with no sign of damage or dirt. Checked the CPUs as well, found no problems either.
I also tried removing memory (those FB-DIMMs are a bit power hungry) but again, there was no difference.
Then I started wondering what would happen with just a single CPU. And that finally got me somewhere.
I established that on both boards, the first socket (labeled CPU1) simply won’t work. That is to say, if the board is powered up with just CPU1 populated, the CPU gets warm(!) but the power indicator LED on the board doesn’t light up and there is no sign of life from the board except for the fans spinning.
Except about twice, the LED did light up… and nothing further happened.
On the other hand, if only the second socket (CPU2) is populated, the board’s power LED lights up instantly, the system POSTs and boots, and the CPU runs at the correct frequency.
The same thing happens with both of the X7DBE boards and all the CPUs I tried. Xeon 5050, Xeon 5080, Xeon 5110, Xeon E5430, Xeon E5450. I did not find any broken CPU, they all worked in the CPU2 socket. Only the first socket on both boards refuses cooperation.
Note that the board documentation says nothing about running with a single CPU. But there is evidence that it’s somewhat commonly done, and good evidence that on this particular board model, a lone CPU in the first socket should work.
Answer, or a Question?
The conclusion, such as it is, appears to be that both boards have some damage on the first socket. How did both boards get damaged in a short time window in exactly the same way is the real mystery, since there is no visible damage on either of the boards.
How that happened with no apparent damage to any of the CPUs is a further mystery. Given that there is no visible mechanical or electrical damage, perhaps the problem is micro-cracks in the boards or something of that nature. Whatever it is does not prevent the CPU in the first socket from drawing power (since it gets warm) but does prevent it from being detected.
Whatever the cause of the problem is, it’s very vexing and annoyingly mysterious.