Heres something new for you: an Intel Xeon E5405 @ 2.0 GHz with 12 MB cache and 1333 MHz FSB is not the same as an Intel Xeon E5405 @ 2.0 GHz with 12 MB cache and 1333 MHz FSB. Uh... what? Yes, exactly, thats what my co-worker Thom and I thought as well. To the untrained eye, this would seem like a steaming pile of bullshit, but unfortunately, it is the truth, the whole truth and nothing but the truth. Allow me to explain.
Two weeks ago we ordered a new web server. Since were going to do clustering, it seemed logical that we get the exact same server as we already had; so we would have two identical servers doing the clustering. The new setup would be running on the Microsoft Windows 2008 Web Edition X64 operating system; the same operating system Im going to run on my own server (which, by the way, is almost done 
) So this morning, Thom and myself fired up the new server with the Microsoft Windows 2008 Web Edition X64 DVD in it, and
What the hell? 
A blue screen of death during setup? That cant be good
A quick search on the error code told me that it means that the processors are not the same. For example, a Pentium processor and an 80486 processor, as Microsoft puts it. But Im pretty sure that we have two identical processors: two times the Intel Xeon E5405 @ 2.0 GHz with 12 MB cache and 1333 MHz FSB. It turns out that there are multiple revisions of the E5405, and Windows 2008 regards that as non symmetrical multiprocessing.
A bit of research later the cookie was cracked. It turns out that one of the processor we were using, a Xeon 5405 of the sub-type SLBBP, was designed in August 2008; which was later than the BIOS (which was of 2007). Which in turn meant that the BIOS version that we were using does not recognize this sub-type of Xeon 5405 because it doesnt know of its existence. An update to the latest BIOS fixed the problem. All in all it was an interesting challenge. 