Hurrah. I think I've established that the spare RAM I have sitting in a box is not compatible with the server I was planning to put it in (at least, alongside the other RAM it's already got), so that saves a job.

To be specific, the machine currently has 48GB in 6 sticks and I have another 48GB in 12 sticks, so I could have doubled its capacity without buying anything, which would be nice, but I'm pretty sure now that the current RAM is RDIMMs and the spare RAM is UDIMMs, and the machine can't have mixed DIMM types, so that's that. Someday I might grab 24×32GB off ebay and max this server out with 768GB total (or maybe cheap out and go to 24×16GB for 384GB total), but… not today!