Memtest86 will only notice a bit-flip by sheer luck: the flip has to happen between when it wrote and when it reads back a short time later. Any flip in bits it

Memtest86 will only notice a bit-flip by sheer luck: the flip has to happen between when it wrote and when it reads back a short time later. Any flip in bits it is not immediately looking at will slip by. Memtest86 is not magic. It is designed to look for systematic failures, even if intermittent. It does that pretty well given it has only bus-level access.