Bottom view of RK05 disk platter. This side of the disk looks ok. Damaged side ( 47k) The center of the disk is a conical hole which centers it on the drive spindle. The flat area is where the spindle magnetically clamps to the disk. The ridge around the hub has small slits in it which are the sector marks and the sector 0 mark.
More or back to RK05 pictures [an error occurred while processing this directive]