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big difference in performance with ECC RAM in iMac Pro vs regular RAM?
- Thread starter Luba
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Error-correcting code memory (ECC memory) is a type of computer data storage that can detect and correct the most common kinds of internal data corruption. ECC memory is used in most computers where data corruption cannot be tolerated under any circumstances, such as for scientific or financial computing.
https://en.wikipedia.org/wiki/ECC_memory
https://en.wikipedia.org/wiki/ECC_memory
So with regular RAM when there's an error, it'll corrupt the data, correct? But I guess it's rare since I don't hear people complain that their data has been corrupted.
According to wikipedia, it can be 2% slower but that the gap is closing or closed nowadays.
Typically, the cycle times of any ECC memory is at most a few cycles slower than non-ECC memory of the same variety (CAS timings for example). The actual bandwidth is identical to non-ECC memory of the same speed. It is only in memory-latency-sensitive applications that you may notice the 1-2% difference.
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ECC can correct error up to a certain number of bits (I think, from memory, don't quote me on this: 1 out of 64 bits is correctable and 2 out of 64 bits is detectable, 64 bits being the word length in binary). Regular memory is thought to encounter errors occasionally depending on both internal (e.g., heat) and external factors (e.g., ionizing radiation). Realistically, people do not complain that their data has been corrupted largely due to the low error rate (which is about 1 in a few years). However, for certain extremely sensitive applications (e.g., high accuracy simulations) with large memory footprints, even that low rate I mentioned is too high. It all depends on what your usage can tolerate. For consumer usage, a 1 bit error in a video stream or texture storage for a game is unlikely to be even noticeable. For a lot of numerical simulations (e.g., fluid dynamics), a 1 bit error could propagate downwards in time and ruin months or years of continuous work.
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Typically, I have heard of a single unrecoverable error per few years. I'm not sure if these numbers are still correct today. There were some situations with certain types of RAM, as an example, in the last few years that would fail what's so called the "HAMMER" (not with a physical hammer) test. These RAM are more prone to certain types of unrecoverable errors that were not frequent.