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- Re: Can volatile RAM still contain evidence?
December 22, 2008, 10:42 pm
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Probably not, but I won't say never. About 1975 or so I remember
buying some of the first 16k RAM chips, I believe from Electronic
Associates. They worked, were reasonably priced, but used 24 pin
DIP sockets as I remember. I found, by accident, that they would
retain their contents for something like 24 hours with all power
removed (to ensure that I removed the card from the system).
I even advised EA of this, but they just disappeared. At the time
development of an electrically rewriteable ROM would have been
valuable - the only thing available was UV erasable EPROMS. I
never took advantage of their characteristic, as I had no idea how
reliable it was, and my end use was medical instrumentation.
[mail]: Chuck F (cbfalconer at maineline dot net)
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Re: Can volatile RAM still contain evidence?
Those would be static RAM chips. The data bits were stored in
flip-flops, which means two MOS transistors per bit. Each bit
retained its state until changed, or power was removed. As you
found out, the MOS transistors could retain their charges for
a time after power was removed. Static RAM was expensive,
but very fast and required minimal support cicuitry. I still have
a bunch of TI TMS4044 18 pin 4k static RAM chips.
Then along came dynamic RAM that required only one transistor
per bit, but required constant refreshing, as the data bits were
stored on tiny capacitors that would lose their charges in a fraction
of a microsecond. Dynamic RAM was a lot less expensive, and
able to be packed into large capacity, dense arrays. Now we have
densities of 2 gigabits per chip.
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