Comment Re:Sweet. (Score 1) 356
Sure they use spares for the word and row lines. Almost always have. Usually use links whcih can be cut with a laser to change the connections. Some programmable styles like EPROM and E^2PROM can program the fix into special registors (assuming they themselves are working). Memory cells can be sorted into about five bins:
Good: self explanitory
Bad Row/Word line: laser a fix, retest
Bad Address decoder: Some rows either read and/or write simulatiously or not at all. Mostly it works, but not all bits can be used. Might be able to laser a fix.
Random bad bits: Well, random
With bad decoders or too many bad rows, disable the bad part and only use 1/2 or 1/4 of the memory.
Chips with random failure have a huge market: Digital voice recorders and cheap music player. Scramble the addresses going in, so the bad bits are mixed up. It doesn't really matter if a few bits are bad in you answering machine or cheap MP3 player!
Good: self explanitory
Bad Row/Word line: laser a fix, retest
Bad Address decoder: Some rows either read and/or write simulatiously or not at all. Mostly it works, but not all bits can be used. Might be able to laser a fix.
Random bad bits: Well, random
With bad decoders or too many bad rows, disable the bad part and only use 1/2 or 1/4 of the memory.
Chips with random failure have a huge market: Digital voice recorders and cheap music player. Scramble the addresses going in, so the bad bits are mixed up. It doesn't really matter if a few bits are bad in you answering machine or cheap MP3 player!
