I'd always wondered why that was so.It has been handy to see which were 360K as I don't think HD everhad the donut ( maybe rare ).Dwight
On Sun, 16 Aug 2015, Chuck Guzis wrote:
Where I saw the problem was with the Micropolis 77-track (single sided) 100 tpi drives.
Their 35 track 48tpi ss drive was the same. Exceptionally sturdy and reliable drive, but not much slope on that cone, and the helical lead screw wasn't intended to step very fast.
Hub reinforcers were on the later 300 Oersted disks. OR user added to early 300s and to 600 Oersteds.
A disk without a hub ring could be either an early 360K or a 1.2M So, they weren't an especially reliable way to identify disks. Adding hub rings to 8" disks made for fewer issues for centering. IFF installed right - an off-center hub ring makes for even more fun.
