The PCMCIA Card Standard provides physical specifications for three types of PC Cards, with additional provisions for extended cards. All three card types measure the same length and width and use the same 68-pin connector.
Because they differ only in thickness, a thinner card can be used in a thicker slot, but a thicker card can not be used in a thinner slot.
Type I
Length: 85.6 mm
Width: 54.0 mm
Thickness: 3.3 mm
Typical Usage: Memory (SRAM Flash, etc)
Type II
Length: 85.6 mm
Width: 54.0 mm
Thickness: 5.0 mm
Typical Usage: I/O (Modem,LAN,etc)
Type III
Length: 85.6 mm
Width: 54.0 mm
Thickness: 10.5 mm
Typical Usage: Rotating Mass Storage
While any card can theoretically be used for any device, due to their size differences, the card types each fit the needs of different applications. Oh, and by the way, post in the right forum next time. There is a big ass read post 4 above this one saying DON'T POST THIS HERE.