So bus passes operate on low density flash - OK, so what's that?

Question

So bus passes operate on low density flash - OK, so what's that?

Answer 1

"Flash" = flash memory: A type of electrically eraseable programmable read only memory (EEPROM).  Flash refers to the method in which the EEPROM is programmed and erased, internally.  This type of memory is called non-volatile.  Power is applied by inserting it into the bus-pass reader.  The information can then be read and changed in the flash memory, but the flash chip will retain that information when the power is taken away.  The information is retained for decades (so they claim -- but I have yet to hear of a flash retention failure).

"Low density" = The amount of memory is less than 128 Megabytes.  In the case of the bus pass chip, it is probably only on the order of 100s of bytes.

There is enough memory to store your name, bus pass ID number, the number of trips you have taken or the number of trips you have left, and authentication numbers for the bus pass reader.  There may be additional information stored, as well.  Everytime you put the flash card into the reader, it retrieves the information, verifies that you still have enough trips or money left, and probably changes the number of trips or the cash amount you have remaining.

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