SUMMARY: Not-so-volatile volatile memoryRe: SUMMARY: Not-so-volatile volatile memory

[Anonymous]

> -- Summary: Data retention in semiconductor memory --
> 
> Contrary to conventional wisdom, "volatile" semiconductor memory
> does not entirely lose its contents when power is removed.  Both
> static (SRAM) and dynamic (DRAM) memory retain some information on
> the data stored in it while power was still applied.  SRAM is
> particularly susceptible to this problem, as storing the same data
> in it over a long period of time has the effect of altering the
> preferred power-up state to the state which was stored when power
> was removed.  Older SRAM chips could often "remember" the previously
> held state for several days.  In fact, it is possible to manufacture
> SRAM's which always have a certain state on power-up, but which can
> be overwritten later on - a kind of "writeable ROM".

Is this a new discovery?  When I used to work with DOD classified
data, not so long ago, disk drives had to be declassified using an
approved program, such as Norton Utilities' "WIPEINFO".  (That was
approved up through the SECRET/SAR level, anyway.  I don't know
about TS/SCI/SI.)  But those same regulations said that RAM was
considered declassified within a certain time (30 seconds, I think)
after power was removed.  (That time figure was UNclassified, BTW.)
I think it was just to allow time for the voltage to bleed off of
the power supply's filter capacitors, and not related to the
relative volatility of DRAM.