27 Dec
2010
27 Dec
'10
11:42 a.m.
On 27 Dec 2010 at 19:19, Tony Duell wrote:
the original HP 3.5" drive unit -- the 9121 was
designed ot be exactly
compatible with the 82901 5.25" drive unit. The latter was a 35
cylinder 2 head deevce, so 70 physcial tracks. The 3.5" drive
therefore only used 70 physicla tracks too. But HP also had this idea
f having 'spare' tracks so that slightly defective disks would appear
perfect to the user. And this was handled by the drive unit. There's
soem kind of infromation stored o nthe inntermost track whih gives the
track replacemtn indromation, disk usage count, etc. No hP maual that
I've seen has any real details of this.
I wonder if it was universally implemented on HP gear. I've seen HP
150 Series I floppies with clusters marked bad the usual MS-DOS way.
You'd think that such a thing would be impossible with an active
"alternate track" scheme.
--Chuck