this post was submitted on 13 Feb 2025
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Am I a moron? or is something up with this RAM? (lemmy.world)
submitted 4 days ago* (last edited 4 days ago) by ch00f to c/[email protected]
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Upgrading a server for the first time in 10 years, so I’m a little out of the loop. I was surprised to find that the RAM I bought didn’t fit.

This is my first time dabbling in ECC RAM, so I figured there was some minor detail I missed when purchasing, but I eventually came across the data sheet for this stick, and the dimensions given don’t match the measurements I’m making. The tip of the caliper should be in the middle of the notch at 68.1mm.

What’s more is that the dimensions in the data sheet seem to match the dimensions on my motherboard. What’s going on here?

[SOLVED] I and Kingston are morons. I ordered RDIMM instead of UDIMM. The Kingston datasheet gives the wrong dimensions.

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[–] [email protected] 11 points 4 days ago

Since you're upgrading, measure it against the stick you removed.

Also, you sure you're not just putting it in backwards? Some put chips and stickers on one side, some on the other. There's no front or back to RAM.

[–] [email protected] 8 points 4 days ago

Different DDR versions have the notch at different places. Server is probably DDR2 or 3.

[–] [email protected] 7 points 4 days ago (1 children)

You try flipping it around? The notch isn't centered

[–] ch00f 2 points 4 days ago* (last edited 4 days ago) (1 children)

Nope. Doesn't work either way. The stick is 133.36mm wide which matches the datasheet, so measured from the other side, the notch should be at 65.25mm. Still not ~~68.1mm.~~ 62.67mm that I measured.

[–] [email protected] 3 points 4 days ago (1 children)

133.36-65.25 = 68.11

Are you sure you zeroed out your calipers correctly before taking the measurement in the photo?

[–] ch00f 3 points 4 days ago (1 children)

My bad. Used the wrong numbers. The notch as measured is 62.67mm from one side and 70.70 from the other.

[–] [email protected] 2 points 4 days ago* (last edited 4 days ago) (1 children)

I think that matches the RDIMM keying although that information is oddly hard to find online.

https://www.mouser.com/datasheet/2/671/ddr5_rdimm_core-3310292.pdf

Page 24 has dimensions but you have to do some arithmetic to actually get the slot center of 62.8mm and 70.55mm

So I think the kingston spec sheet has the wrong drawing that shows UDIMM dimensions.

I think you need to return the RDIMM and get UDIMM, or switch motherboards.

[–] ch00f 2 points 4 days ago

oddly hard to find online.

Right? I was hoping for like a wikipedia page with the dimensions of every kind of DIMM. Might have to make one...

So I think you're right. The only explanation is that I ordered RDIMM instead of UDIMM and that Kingston messed up.

I just double checked, the compatibility checker suggested the -EU variant, but I was looking at -ER. (Un/Registered).

It doesn't help that ECC and registered get interchanged a bit it seems.

[–] ch00f 6 points 4 days ago* (last edited 4 days ago)

More details, the motherboard is a SuperMicro H13SAE-MF. Its manual says it supports ECC/Non ECC UDIMM DDR5. I'm out of the loop, but I believe UDIMM means "unregistered," which would explain why my RDIMM isn't compatible, but the SuperMicro website compatibility checker suggests ~~this stick which says ECC REG DIMM in its detailed description.~~ wrong, that's the ER version. The checker suggests EU.

What's going on?

[–] tabular 5 points 4 days ago* (last edited 4 days ago) (1 children)

ECC is always the same size as non-ECC, so it should fit (at least on the AM4 platform, last I looked into ECC RAM)

Also, I wish they wouldn't put important information on the stupid "warranty void if removed" sticker. I really wanna rip it off.

[Glad you solved it]

[–] ch00f 1 points 4 days ago (1 children)

What about UDIMM and RDIMM?

[–] tabular 1 points 4 days ago (1 children)

Didn't see anything about ECC being a different size for UDIMM and RDIMM (from a quick search).

That data sheet says "Tolerances on all dimensions are ±0.15 (millimeters)". Perhaps it's just a tight fit - does it look like it will almost fit? It wouldn't be anything to do with the motherboard RAM slots, like they need to be "opened" fully?

[–] ch00f 1 points 4 days ago

This is pushed all the way to the right.

[–] [email protected] 3 points 4 days ago (1 children)

Is there some chance an unreputable seller has sold you a mislabeled stick?

[–] ch00f 2 points 4 days ago* (last edited 4 days ago)

Got it from Newegg. Also even if it's mislabeled, what kind of stick is this supposed to be?

[–] kn33 1 points 4 days ago (1 children)

I'm at dinner but I can try to look it up later. If you want to try, though, look for the physical specification for various DIMMs

[–] ch00f 1 points 4 days ago

I found this datasheet that seems to more or less perfectly match the stick I got:

https://www.kingston.com/datasheets/KSM56R46BS8-16HA.pdf

The specifications are also very similar to the datasheet for the stick I got. I'm wondering if neither of these sticks are compatible with my motherboard, and Kingston just pasted the wrong graphic on the datasheet for the stick I ordered.

[–] [email protected] 1 points 4 days ago (1 children)

Are one of the clips on the slot not opening all the way?

[–] ch00f 1 points 4 days ago

I've tried it for a bit. No luck.

Also, if I measure the slot itself, it seems to align with the dimensions given in the RAM datasheet just not the RAM stick itself.