Without going too far into it, the SD memory card is much smaller than the Compact Flash card. However, it was my understanding that the SD memory was supposed to be a replacement for for smartmedia cards which are going to shortly hit a maximum storage ceiling. Compact Flash still has a ways to go and larger sizes of SD memory have been announced along with additional companies that will manufacture the cards. This should bring the price down so it's more competitive with the other storage options.