A form of flash memory is called Compact Flash. Although they are also used in PDAs and handheld audio players, compact flash cards are most frequently used to store images in digital cameras.

Compact Flash devices come in two distinct varieties called Type I and Type II. Cards of Type II are 5 mm thick, while Type I cards are 3.3 mm thick. The "MicroDrive" card from IBM is the same size as a Type II CF card but is built from a real hard drive as opposed to flash memory. Initially only able to hold a few megabytes of data, Compact Flash devices can now hold several terabytes. A total of 137 Gigabytes of data can be stored using the new CF+ standard. I don't know about you, but before stuffing the card in my wallet, I'd consider backing up that data.