xD Picture Card
The xD Picture Card is a storage solution made by Fujifilm. Small and lightweight, it has high write and read speeds. It is also durable and not susceptible to slight vibrations that occur with normal camera use. The xD Picture Card can be used with cameras that are xD Picture Card--compatible or with an adapter that allows the xD Picture Card to be inserted into a Compact Flash slot.
Compact Flash Type I
A Compact Flash Type I card is larger than an xD Picture Card but smaller than the microdrive. It measures 43 mm x 36 mm x 3.3 mm. Compact Flash cards are made with flash memory, a nonvolatile form of storage. Unlike drives, this type of data storage does not drain the battery life of your camera. There are no moving parts so your data is safer. Compact Flash cards are also compatible with some DSLR cameras.
Microdrive
Microdrives are actually another form of Compact Flash card, specifically Compact Flash Type II cards. They are slightly thicker, at 5 mm instead of 3.3 mm. Microdrives do have moving parts and are therefore susceptible to impact and resultant data loss. The drives are made to handle regular camera use, however, and users have reported success with them. Microdrives use more power than Compact Flash Type I cards because of the need to power the moving parts during use.
Choosing a Storage Card
The type of card you use depends on a number of factors. If you have other cameras, choosing the card that is also compatible with those cameras will allow you more use from the cards. xD Picture Cards and Compact Flash Type I cards are resistant to data loss from bumps along the road and are more suitable for photographers who shoot in rugged areas with a lot of action. Microdrives are not recommended for use in situations where you get bumped a lot as you photograph on location.