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As newer DRAMs advance into smaller process geometries, we
are seeing in increase of chips that contain "weak"
bits. These are chips that may have a microscopic defect in
an individual cell. This defect is not enough to cause a failure
outright, but will start exhibiting itself after of few months
of field operation when a DIMM module has been installed in
an end customer's facility.
DRAM modules, like most other electronic components, follow
a well-known reliability curve called the "bathtub curve".
The phenomena shows that most of the failures occur during
an early life phase which will typically span a few months
of field operation. At that period's conclusion, the component
will go through a highly reliable useful life phase which
will last as long as 20 years. Eventually, the component will
start to wear out, although not before functioning for a very
long time. Most electronic components never get to the wear-out
phase because they the system normally become obsolete and
are replaced with more modern technology long before the component
reaches the wear-out phase.
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