21
Jul
06

Beware the VRM

Sometime this spring our research group acquired a rack of Compaq ES40 server machines for free courtesy of MIT’s reuse email list. During the last few months we’ve been working periodically on getting it set up for our purposes. This has included installing Debian GNU/Linux and getting two 30 amp plugs installed in the room where it sits. While this machine is pretty sweet (4 nodes; 4 Alpha processors/node), it does have some shortcomings. Most notably, it is very low on hard drive space: each node has only a 9GB hard drive. To remedy the storage problem, I had been thinking about putting together a fileserver on which we could mount each user’s /home directory over NFS. Toward that end, I recently acquired a Dell GX300 with a Pentium III 800 MHz processor for free from the MIT Equipment Exchange.

Since our “new” fileserver came with only a 15GB hard drive, I bought a new 80GB boot drive and two 160GB hard drives to serve as a RAID1 array. Given that the motherboard supports two processors, I figured I could upgrade the computer on the cheap by adding another processor. This turned out to be a little tricky because I had to make sure that the two processors would work together. The easiest way to do this is to make sure that the so-called sSpec number is the same on both processors. (See this link for useful information on the whole line of Intel processors.)  After locating the sSpec number on the existing processor, I located some other SL4BX processors on eBay and ended up buying one for ~$28. This was not the cheapest SL4BX I found but it was the only one that was guaranteed to have a heatsink compatible with my computer case, so it seemed like the best choice.

This morning, after receiving my new used SL4BX, I installed it only to find that it didn’t work. While both processors work individually, I got a strange error message about a voltage failure when I tried to use both at the same time. So, I consulted the online documentation only to find that, in order to use two processors, an additional component is needed: a voltage regulator module (VRM). I had noticed a strange-looking plug on the motherboard before and wondered what it was for. It’s for the VRM. Back to eBay.

I looked around for quite awhile simply trying to figure out what part I needed. This useful piece of information was conspicuously absent from the Dell online documentation. Gradually, it became clear that I needed Dell part number 7649D, which is apparently identical to part number 11GEF, which is the same as part number 05S2020A-4 from some company named Delta, which apparently made these parts for Dell. I called Dell Spare Parts and the guy confirmed that the part I needed was the 7649D. From looking at photos online I was able to convince myself that the 7649D is the same as the 05S2020A-4 and that the 11GEF is the same as the 05S2020A-4. In any case, after pricing the 7649D and 11GEF, I came to the disheartening conclusion that the VRM was going to cost at least as much as the processor. In fact some used equipment retailers were asking as much as $100 for this part. In the end, I lucked out and found an 11GEF for the “Buy it now” price of $17.95 + $8.60 shipping. Thus, I managed to get the VRM for about $1.50 less than the processor. Despite finding the VRM for a reasonable price, this upgrade turned out to not be as cheap as I had anticipated.

I should have the part on Monday or Tuesday and the moment of truth will present itself. I really hope that everything works, otherwise I will have wasted scarce research funds on a wild goose chase for old computer parts. However, if everything does work, I’ll have a pretty sweet server machine on the cheap: Dual Pentium III 800MHz, 512MB (Rambus) RAM, 80GB boot drive, 160GB RAID1 Array for ~$250. Acknowledgements: MIT Equipment Exchange (base machine), Microcenter (hard drives), eBay (SL4BX, 11GEF).

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1 Response to “Beware the VRM”


  1. 1 Your Wife
    July 21, 2006 at 11:14 pm

    I like your acknowledgements at the end.


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