> The industry developed UV-erasable EPROM as a substitute, which allowed
> only the erasure of the entire memory chip, , and some early EEPROM.
> (Electrically erasable programmable Read-Only-Memory).Eventually
> "flash-EPROM" was developed.
Flash memory
| | Flash memoryFlash memory is an electronic (solid-state) non-volatile computer storage medium that can be electrically erased... |
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>Ah, I hadn't made the connection between FLASH drives and Flash
EEPROMS. However, this pushes the question back: how would an
EEPROM do it? Old PROMs used to burn fuses to maintain state, but how
to restore state, eh?
>I believe that one could make flash drives that start at all-1s and
then burn the 0s into the memory. A small battery-powered device
could maintain the address of the next writable word, otherwise once
the device reached the end of memory, it would no longer be useful
for. writing.
These devices injected a tiny electric charge into a "floating gate", an otherwise-insulated conductor surrounded by an extremely good insulator.
The level of insulation required was phenomenal: In order to store a bit of data for many decades, an effective resistance of over 10*20 ohms would have been necessary. If you assume a capacitance of one picofarad (10E(-12) farads) in parallel with 10**20 ohms, that's a time constant of 10**8 seconds, or 3 years.