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Salvaging Defective DRAM
An anonymous reader writes "Ever wonder what happens to DRAM that fails quality assurance testing during manufacturing? Turns out a lot of it ends up as 'downgrade' memory and ends up in OEM memory modules. Last resort: use it in an answering machine, where the sampled audio can be very tolerant of bit errors."
There are a lot of peeps complaining about substandard ram. If you had RTFA, you'd realize that the downgrade ram is reconfigured to skip the bad parts in the chips, so that it comes out as a normal module. Just because there is a faulty bit or 10 in a modules, doesn't mean the reast of that module is bound to fail. It could just have been an imperfection in the silicon or the circuit process.
You have made a statement that makes it very clear you are a very educated layman, not someone in the field. What you've said is true to the first order, but not inherantly true.
Wafers have what can be measured as "defect density", and observe a phenomena called "defect clustering". Defects are not always hit or miss, open or short, some of them are latent or resistive. As the part ages (diffuses), electromigrates or observes hot electron effects, all parts will decrease in quality. Downgrade RAM, so to speak, would be most likely to have additional cells fail due to the above effects -- because it had failures that made it marginal in the first place. Testing methodologies at higher quality manufacturers build in guardbands to make sure that nobody ever experiences the defects when used in-spec. (This is why many overclockers lose their chips after only a year or two, they cause latent defects to surface and suddenly the chip won't even operate at nominal frequencies; the guardband effect also explains to a great degree why many chips can be overclocked in the first place.)
I'm not dis'n you, just trying to fill in a few more holes.