Currently there are 3 standardized PC Card physical form factors:
Type I is the original 3.3 mm thick card. These cards have their application in memory devices such as Flash, OTP, and RAM. However, modems and other devices also are included.
Type II expands the thickness to 5.0 mm. These are typically used in I/O devices such as data / fax modems, LANs, and also mass storage devices. Type II cards are the most sought after size today and are used for most functions barring a few special applications.
Type III further expands the thickness to 10.5 mm and is used for devices whose components are thicker, such as hard drives.
The latest release of the PC Card Standard provided information to improve compatibility and added support for features such as 3.3 volt operation, and DMA support.
