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Comment by WatchDog | Hacker News Reader

All DDR5 ram has some amount of error correction built in, because DDR5 is much more prone to bit flipping, it requires it.

I'm not really sure if this makes it overall more or less reliable than DDR2/3/4 without ECC though.

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As I understand it, DDR5's on-die ECC is mostly a cost-saving measure. Rather than fab perfect DRAM that never flips a bit in normal operation (expensive, lower yield), you can fab imperfect DRAM that is expected to sometimes flip, but then use internal ECC to silently correct it. The end result to the user is theoretically the same.

Because you can't track on-die ECC errors, you have no way of knowing how "faulty" a particular DRAM chip is. And if there's an uncorrected error, you can't detect it.

that doesn't help when the bit is lost between the cpu and the memory unfortunately, it only really helps passing poor quality dram as it gets corrected for single bit flips, not that reliable either it's a yield / density enabler rather than a system reliability thing.

it's "ECC" but not the ecc you want, marketing garbage.

DDR5 on-die ECC detects and corrects one-bit errors. It cannot detect two-bit errors, so it will miscorrect some of them into three-bit errors. However, the on-die error correction scheme is specifically specially designed such that the resulting three-bit errors are mathematically guaranteed to be detected as uncorrectable two-bit errors by a standard full system-level ECC running on top of the on-die ECC.

ECC also reports error recovery statistics to the operating system. Lets you know if any unrecoverable errors happened. Lets you calculate the error rate which means you can try to predict when your memory modules are going bad.

I think this sort of reporting is a pretty basic feature that should come standard on all hardware. No idea why it's an "enterprise" feature. This market segmentation is extremely annoying and shouldn't exist.

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