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Memory chips are simply
a collection of
registers , each with
its own address.
Data, in the form of 0's
and 1's, is stored in
the registers.
ROM chips can be read
from, but not written
to.
They are non volatile,
which means that they
retain their contents
after power is removed.
Most ROMs are programmed
during manufacture of
the chips.
Others, PROGRAMABLE
ROMS, PROMS, can have
their contents
programmed in after
manufacture.
The 2716 ROM shown above
is an EPROM.
This is an erasable
prom, where if you make
a mistake, you can erase
the contents by shining
ultra-violet light
through a window in the
chip.
Some chips are
ELECTRICALLY ERASABLE
and are known as EEPROMS.
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