I&#x27;d imagine it&#x27;s more likely to be the engineering tolerances required to keep the vertical movement to a minimum at double the radius? But I have no real insight, just a guess.<p>It does strike me though - why do disks do serial reads, couldn&#x27;t the head read several tracks at once? Why not have several heads angularly spaced around the drive? Presumably such things have been tried and found lacking in some respect. Looks like I need to do some research ...