[RoSs_bg2_rox]

Well, small mp3 players (memory based ones) usually use disposable batteries, where as hard drive ones have there own rechanrgable ones. (like say a digi cam battery or something)

The difference basically is the memory based ones are smaller, yet dont hold as much and dont have as much features, where as the hard disks are larger, cost more, but hold more and have bigger screens and lots of features. Personally I prefer Hard Disks, having had both, although the hard disk ones are starting to become smaller and soon will likely be the same size as the small ones.