Slashdot Mirror
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."
Comment removed based on user account deletion
Very true. I'll never buy generic RAM simply because it is more likely to malfunction. I've seen this happen to many of my friends. I'll stick with my Kingston RAM. The extra price is worth the warranty and the ability to sleep knowing my RAM won't mess my computer.
'Give me one more medicated peaceful moment'
If more people did a little research when they bought computers, or computer parts, they wouldnt have half the problems. Instead they listen to the sales people, or they buy the cheapest thing they can find and then wonder why their system locks up.
I wish more people would do this and not just for memmory, but for any big purchase. It's one of the truly great aspects of the internet, fast cheap research.
sig: There are two mistaakes in this sig.
Defective hardware is distributed to the nearest geeky friend, i myself have a shelf and a spare desk with drawers full of old/non working hardware. I'm sure you average /. reader has at least this if not a spare room full of old 286 boxes.
"Sic Semper Tyrannosaurus Rex."
If the chip is half-bad, there are good chances that it has defects in the other half. Usually, it's a problem with the process and not just random quirks. It's just that one half works better than the other. In fact, many windows crashes are not caused by Windows, but by bad RAM. And good luck finding anything with memtest86. Once, I ran that program for about 3 hours on a machine with bad RAM. It didn't find anything. When I replaced one of the sticks, all the problems went away.
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.
This is why I stopped using answering machines and started using the voice messaging at the telco. Millions of little plastic boxes eating up electricity in millions of homes is bound to be less efficient than voice messaging at a central server.
The services at the telco let people leave messages when I am on the phone.
System bus(and SRAM) is driven by transistors. So its kept in 1 or 0 state rather forcefully, a single particle hitting it is not likely to change its state. DRAM on the other hand is a really huge ass array of really tiny capacitors. It's a small wonder it works in the first place and you only need a minuscule amount of energy to change single bit's state.