I would love to see DDR4 vs DDR5 bitflips. As I understand it DDR5 must come with some level of ECC [1].

[1] https://www.corsair.com/us/en/explorer/diy-builder/memory/is...

From Corsair

>> DDR5 technology comes with an exclusive data-checking feature that serves to improve memory cell reliability and increase memory yield for memory manufacturers. This inclusion doesn't make it full ECC memory though.

"Proper" ECC has a wider memory buss, so the CPU emits checksum bits that are saved alongside every word of memory, and checked again by the CPU when memory is read. Eg. a 64 bit machine would actually have 72 bit memory.

DDR5 "ECC" uses error correction only within the memory stick. It's there to reduce the error rate, so otherwise unacceptable memory is usable - individual cells have become so small that they are not longer acceptably reliable by themselves!

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kevin_thibedeau a day ago | parent | prev | next [-]

DDR5 comes with marginal DRAM that is patched up with ECC to boost yields. It's not the same as fully reliable RAM.

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Aurornis 21 hours ago | parent | next [-]

The net error rate is lower with the internal ECC.

DDR4 is not fully reliable memory either.

This is common for many high speed electrical engineering challenges: Running a slightly higher error rate option with ECC on top can have an overall lower error rate at higher throughput than the alternative of running it slow enough to push the error rate down below some threshold.

It makes some people nervous because they don’t like the idea of errors being corrected, but the system designers are looking at overall error rates. The ECC is included in the system’s operation so it isn’t something that is worthwhile to separate out.

	▲	Dylan16807 15 hours ago \| parent [-]
		Yeah, while it's good to be wary of error levels, the version of a hardware system where they decide they need error checking/correction is probably a lot more reliable than the version before it. A bit error rate of one per billion with a parity bit on each packet is much more reliable than a undetectable bit error rate of one per trillion.

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stinkbeetle a day ago | parent | prev [-]

Similar to CPUs, where many arrays have spare yield capacity, even whole cores can get disabled (and possibly sold in a different bin). DRAM stores redundant electrons in capacitors to patch it up and boost yields. Everything in reliability is a spectrum.

"ECC" does not give you fully reliable RAM. UEs are still be observed.

What's the chance of fail? If you have one device that achieves equal performance with less reliable cells and redundancy to another device that uses more reliable cells without redundancy, it's not really any different.

NAND is horribly flaky, cell errors are a matter of course. You could buy boutique NOR or SLC NAND or something if you want really good cells. You wouldn't though, because it would be ruinously expensive, but also it would not really give you a result that an SSD with ECC can't achieve.

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silon42 17 hours ago | parent | prev [-]

I wish also for desktop vs laptop ram comparison.