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From: jsims@vuse.vanderbilt.edu (J. Robert Sims)
Newsgroups: comp.sys.handhelds
Subject: RE: RAM (or ROM) card contents (was: Hidden EQ Li
Message-ID: <9101181749.AA27820@vuse.vanderbilt.edu>
Date: 18 Jan 91 17:49:34 GMT
Lines: 14
To: handhelds@gac.edu
Return-path: <jsims@vuse.vanderbilt.edu>
To: handhelds@gac.edu

Wlodek Mier-Jedrzejowicz asks if anyone else with a firm footing in reality and
their feet on the ground care to comment on nipping the corners of RAM chips.
OK:  here's the modern reality.  Only cheap calculators nip the corners off for
write protection.  The real way to write protect a RAM is to take a small nip
out of the _middle_ of one end.  This creates two quantum wells with opposite
polarity which cancel each other.  The result is that the RAM is write
protected, but the overlapping quantum functions actually reconstruct the bits
that were physically removed.  A RAM chip is like a hologram; each part can
be used to reconstruct the whole.  In this case, the fields are strong enough
to reconstruct the physically missing bits, but weakens the field as a whole
so that writing to any part of the RAM becomes impossible.  Since nipping part
of the RAM does not reduce the amount of memory, the question still remains
of why the EQ lib card is not totally full?  

Rob