Given that external USB drives use slimline 2.5" ATA hard disc units, and the T2 internal hard disc (if I read the manual correctly) is a slimline 2.5" ATA hard disc units.... how can the external unit be cheaper if it is the same capacity.

I suppose if you are going to get the internal hard disc from yamaha or a music store then it's going to be more expensive, but my reading of the Tyros2 manual is that any suitable thickness 2.5" notebook type hard disc will do so I'd go to an internet PC dealer.

I would expect the internal HD to perform better anyhow. I think the Tyros USB is v1.1 (but I might be wrong).