ECC stands for
error correction code, [...]
How much "redundancy" is common?
I don't know enough about other platforms to comment, but on the SPARCs
where I know something about parity/ECC and RAM, non-parity is 32 bits
wide, parity is 33, and ECC is 36. 4 extra bits doesn't seem like
enough to do even SEC to me, never mind SECDED, so I'm not sure how 36
bits can actually provide ECC, but that's what it's called. (For a
32-bit word, there must be at least 32 codewords at Hamming distance 1
that are at distance >1 from all other valid codewords, so there must
be at least 32 times as many possible codewords as valid codewords -
but 4 extra bits gives only 16 times as many possible codewords as
valid codewords.)
Maybe the memory controller actually handles it as 64-bit words with 8
bits of ECC data each or something equally odd.
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