Etienne Lorrain (etienne_lorrain.delete@this.yahoo.fr) on January 7, 2021 1:21 am wrote:
> Jukka Larja (roskakori2006.delete@this.gmail.com) on January 1, 2021 10:28 pm wrote:
> > as there isn't clear information about what that "unofficial" means.
>
> Maybe, just maybe, it is because of the length of an ECC line.
> If I remember well, you can prove/check that up to 32 bits protected by 6 bits, your logical
> SECDED circuitry will always correct one bit error, and always report DED if more than
> one error is present (no triple or more fault error will be detected as a SEC).
> You can't do that if your ECC line is longer, more (or equal) to 64 bits protected by more (or equal) than
> 7 bits, you just have a "strong feeling" it is, but checking every combinations would be too long.
> Same with DECTED, too many combinations.

Isn't ECC overhead 1/8th the cost of the data? Like if you have 8 DRAM chips, the ECC chip would be the ninth one?

Your example of protecting 32 bits by 6 bits is more than that. So I'm not sure if that's cogent or optimal.