The microdrive is for use in digital camera's, pda's etc. The other drive is a small drive..but not near as small, I believe it's what the Apple iPod and the likes use. Some PDA's will take PCMCIA cards, although you need a special adapter normally, and it does get bulk. The microdrive's are tiny, the size of a compact flash card, although they do suck a ton of batteries so you're camera will run out a bit quicker. You're talking the 5gb being about 2-3x the size of the compact flash. I see the microdrive as having a lot more potential, the other is just a small hard drive.