Floppy formatting and using

[Brian Cuthie]

In article <307 at dcs.UUCP> wnp at dcs.UUCP (Wolf N. Paul) writes:
>... DOS will let you use floppies with bad sectors,
>it simply marks them as unavailable in the FAT. If you get a floppy with
>bad sectors, and format it under DOS, the format program will report,
>
>
>	XXXXXXX bytes total
>	   XXXX bytes in bad sectors
>	XXXXXXX bytes available
>
>whereas Uport's format program is a low-level formatting program, which neither
>verifies the formatted floppy, nor records bad sector information (how should
>it, since it doesn't know anything about a FAT, or a freelist.

Actually, there is a way for the uport driver and format routine to handle
bad sectors on floppies.  Instead of having 15 usable sectors per track, you
only use 14.  This leaves one sector per track for alternate mapping.

The disk controller (be it floppy or hard disk) does not care what order the
sectors are in.  Thus assume sectors were normally ordered (use 1:1
interleave for simplicity) 1 2 3 4 5 6* 7 8 9 10 11 12 13 14 XX.  If sector
6 were bad, then it could be remapped by the format program so that the
track was formated in this order: 1 2 3 4 5 XX 7 8 9 10 11 12 13 14 6.  The
controller would never know the difference, since it always searches for the
proper header id before reading/writing a sector.

-brian



-- 
Brian D. Cuthie                                 uunet!umbc3!cbw1!brian
Columbia, MD                                    brian at umbc3.umbc.edu