Is it the old or new Nav?
Also are you asking how large the drive is, or just how much of it is available for you to store music on? Most of the disk is taken up with the navigation maps etc.
On my 'New Nav' I have 20GB available for music. I think the previous system i think it was 10 or 12GB.
Last edited by RichardM; 12-30-2012 at 08:25 AM.