[coreboot] question on erasing flash

Peter Stuge peter at stuge.se
Sun May 17 00:46:03 CEST 2009

ron minnich wrote:
> I've gotten curious: does erasing erased pages count as a 'write
> cycle' against that page?

It probably counts as an erase cycle.

Writing runs a large current through cells, storing some charge in
what is essentially an insulated conductor.

Erasing also runs a large current through cells, but in reverse, to
empty out the stored charge.
http://en.wikipedia.org/wiki/Quantum_tunneling (good graphics here)

I haven't found if a flash cell fails because of the repeated
exposure to high currents when writing or erasing, or because of
the charge transfer that occurs when a cell changes value.

Even if re-erasing an erased cell can be assumed to not be as harmful
as erasing a programmed cell, it will still have an impact on the
lifetime of the cell. Maybe it is negligeable though.

If the important wear is in fact not high currents, but rather charge
moving into or out of the store, as supported by the likening of that
process with an ionization radiation effect, then re-erasing will not
have much of an impact on the lifetime because no charge has to move
around in the cell.

Tom - do you know?


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