4 May
2005
4 May
'05
12:28 p.m.
Jim wrote:
Two words: Track density. Old 5.25" disks
spread (in the case of IBM
PC-land)
Track density is definitely NOT the problem. The track density of a
720K 3.5" floppy is so low compared to the flux density along a track that
the former is essentially irrelevant. Track density is 135.5 TPI, but
flux density ranges from 4885.8 FTPI on track 0 side 0 to 8323.0 FTPI
on track 79 of side 1. (Double those FTPI numbers for 1440K disks.)
The increases to the FTPI were accompanied by changes to the oxide
formulation to have higher coercivity. Most 720K 3.5" disks from the
early 1980s and 1440K 3.5" disks from the late 1980s are fine, though
there was some bad stuff back then as well. But today it seems that
none of it is good. It's definitely the quality of newly manufactured
media at fault, since the older media still works well.
Eric