I've been using the i40M for about 7 years and added the hard drive about 5 years ago. The hard drive is supposed to hold about 7,000 files (I have about 400-500). I have never tried to load styles or programs into the hard drive. If you use a lot of sequences, the hard drive is indespensible. It's very easy to load, easy to playback, easy to use on gigs especially using the Jukebox function. It is very reliable. Musitronics in Germany makes a hard drive dedicated to the i40. The last one I bought was around 120 euros. I don't know of any other hard drive that will work with the i40. Hope this helps.
[This message has been edited by Jerry T (edited 08-27-2006).]