Secure Digital is the card that can fit directly into the iPAQ (slot on top). SD cards are available from I believe 16 Mb all the way up to 512 Mb. I currently use a 128 Mb in mine. The only benefit I can see from using SD is size (fits right in the iPAQ without an adapter sleeve). They are much slower than Compact Flash cards in the iPAQ.CompactFlash cards are about twice the size and thickness and require an add on CompactFlash sleeve to be used in the iPAQ. The benefit of using a CompactFlash card over a Secure Digital card is speed. CompactFlash cards offer a higher bit rate than SD cards do in an iPAQ making CF cards more suitable for streaming MP3 files or video. Also of note - Type II Compact Flash sleeves will accept Microdrives (small hard drive) offering up to 1 GB of storage.
Hope that helps
iPAUL
