I'm working on a server and ordered replacement ECC memory and found that the fully buffered DDR2 to have the notch in a different positions.

I wasn't aware what buffered vs unbuffered memory has a different notch positions. Can someone please confirm?

I couldn't find a reference online for this. I would appreciate links for citation for DDR2 specifically (for my use case) and ideally for other DDR type as well in case things have changed.

The top ram stick is a Hynix HYMP512F72CP8D3-Y5 AC-C. The stick on the bottom is a Samsung M393T5160QZA.

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Yes, they have different positions. This is because they are not interchangeable. If the board needs buffered modules, you can’t use unbuffered ones and vice versa.


  • Thank you. I'd read the Wikipedia article but missed that part. I wasn't sure if it was related to voltage as I think older memory moved the notch around for this. – Zhro Nov 15 '18 at 13:46
  • 1
    @Zhro It did, but the notch movements for voltage were really small (on the order of single-digit millimeters) and did not displace any of the pins. That's what the extra space around the notch was originally for, so that the boards could use an otherwise identical layout of the traces, and just had to have the notch cut slightly differently. – Austin Hemmelgarn Nov 15 '18 at 16:29

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