Duck has it right.
The PCMCIA card may be used to UP or DOWN - load data depending on the function of the unit. They may require formatting like a disk, or not. Older types of FDAU may not have any type of front access or may use a tape or floppy disk, as in a QDR or QAR.
They are also used on other units like EGPWS/TAWS for up and downloading data and programming.
It's all part of the advancement of avionics and the standardization of the avionics suites.
Simply put it's just like the card you buy at Office Max but the innards are configured for the specific application of installing or retrieving data.