Question DDR5 SO-DIMM question: performance of 8 GB vs 16 GB?

[bit_user]

Is anyone aware of benchmarks or other known performance differences between 8 GB SO DIMMs and 16 GB ones? I'm just suspicious because even the 16 GB DIMMs are all single-rank, as far as I can tell, and yet both the 8 GB and 16 GB DIMMs use 16 Gb dies. So I'm wondering if they did something funny to halve the capacity of the chips that might negatively impact performance.

For this application, I don't need more than 8 GB DIMMs and I'm trying to do this on the cheap. However, if there's a major performance difference, I might spend the extra and go with 16 GB.

Just to be clear: I'm planning on using the same number of DIMMs, in either case. This is not a question of 2x 8 GB vs. 1x 16 GB.

Thanks!

 

[CountMike]

Is anyone aware of benchmarks or other known performance differences between 8 GB SO DIMMs and 16 GB ones? I'm just suspicious because even the 16 GB DIMMs are all single-rank, as far as I can tell, and yet both the 8 GB and 16 GB DIMMs use 16 Gb dies. So I'm wondering if they did something funny to halve the capacity of the chips that might negatively impact performance.

For this application, I don't need more than 8 GB DIMMs and I'm trying to do this on the cheap. However, if there's a major performance difference, I might spend the extra and go with 16 GB.

Just to be clear: I'm planning on using the same number of DIMMs, in either case. This is not a question of 2x 8 GB vs. 1x 16 GB.

Thanks!

Modern memory chips are stacked in several layers, unlike earlier ones that had to have more chips on both sides of PCB, hence "DIMM" (Dual Inline Memory Module). Modern ones are made in much higher density by finer fabrication so each chip can have more capacity so less chips are needed for same or more capacity.
For same frequency, latency etc, it doesn't change performance of total RAM stick.

 

[bit_user]

I just found a description of the JEDEC standard configurations for DDR5 UDIMMs. Apparently, three layouts are defined:

• A0 (1Rx8)
• B0 (2Rx8)
• C0 (1Rx16)

This C0 layout is apparently what those 8 GB SO-DIMMs are using. As for the performance aspect of this, I'll just quote from the article I found:

"It is also interesting that with C0 there is a standard for 8 GB modules with x16 ICs. Also with DDR4 there were already such x16 memory chips, which were often used in notebooks or servers, where the raw performance is not as important. Simply said, here one memory chip takes over the work of two, so that already with 4 memory chips a complete module can be built.

This is where the aforementioned banks come into play again, effectively having to do twice the work, often at the expense of performance. But since there are now also twice the number of bank groups per memory chip with DDR5, the performance deficit should at least be less than with DDR4, at least on paper."

Source: https://www.igorslab.de/en/ddr5-dee...ry-standard-and-examples-from-the-practice/3/
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I just wish someone had quantified the performance impact. It's probably been done, but I'm just having difficulty finding it.

The other piece of data I wish I had was on the idle power utilization, per 16 Gb die.

 

[thestryker]

I just wish someone had quantified the performance impact. It's probably been done, but I'm just having difficulty finding it.

I don't know how directly helpful it will be, but GN did a review of a prebuilt Dell that used an 8GB stick configured like this:
Teardown:

View: https://www.youtube.com/watch?v=4DMg6hUudHE

Review:

View: https://www.youtube.com/watch?v=5N7aYtkzKJc


It's the only thing I remember ever seeing with that weird configuration.