The idea that cosmic rays are responsible for DRAM failures seems laughable. I'm surprised anybody ever thought that.<p>I worked in a DRAM fab; I saw how it was made and tested. It's a month-long process involving dozens of machines. Particulate contamination, watermarks, process variation -- there are tons of things that can go wrong. And then testing. There's just no way to test thoroughly enough to catch all of the possible issues with timing and crosstalk. Not to mention electromigration and dielectric breakdown. You can do burn-in, but it's not going to catch everything. We even know which die are most failure-prone (usually edge die, due to process uniformity issues.) If they pass test, they get shipped!<p><i>Of course</i> these issues are manufacturing related.