[dmm]

ECC doesn't protect you from from all rowhammer problems because they can flip more than two bits at a time, the limit which ECC can detect.

"Tests show that simple ECC solutions, providing single-error correction and double-error detection (SECDED) capabilities, are not able to correct or detect all observed disturbance errors because some of them include more than two flipped bits per memory word"

https://en.wikipedia.org/wiki/Row_hammer#Mitigation

[hathawsh]

OTOH, a rowhammer attack on ECC memory will likely flip 1 bit before it flips 2, making attacks theoretically detectable. Without ECC, there's no clear way to detect an attack.

[lolc]

I'd assume that parity is checked on access, which may give enough time to flip more than one bit before it's detected.

[Rebellos]

ECC memory controller performs memory scrubbing periodically, in the background, during which it checks parity and corrects any bitflips. Otherwise ECC would not work nearly as well as it does.

[Dylan16807]

Parity isn't checked during every single row refresh?

[cesarb]

AFAIK, row refresh is done within each memory chip, while the ECC bits are normally on a separate chip (for instance, where a non-ECC module has 8 chips, an ECC modules has 9 chips), so ECC scrubbing has to be done in the memory controller.