formatting and checking floppy disks for bad sectors

[Fred Cisin]

On Sun, 31 Jul 2016, Maciej W. Rozycki wrote:
> There used to be a `fdformat' utility available providing fancy stuff for
> DOS users like sector physical and logical shifting, interleaving, unusual
> geometries, etc.

Be aware that FDFORMAT is ALSO the name of Linux low-level formatter, AND
a Microsoft utility for formatting their 1.7M format.

> You could use physical shifting (track lead and inter-sector gap
> rearrangement) to avoid bad spots in some cases altogether, and logical
> shifting (out of order sector ID assignment) to improve data transfer
> performance -- typically ~twice compared to results obtained with the
> regular `format' utility shipped with DOS.  Some other features were
> available I don't remember offhand anymore; basically you had much control
> over the NEC µPD765 FDC chip itself with this tool's command line options.

If diskettes were seriously hard to come by, then moving sectors around to 
put bad spots of the disk in unused places makes sense.
If I have a known flaw on a disk, I always assume that there are many more 
unknown flaws on the same disk.
Therefore, in the event of a flaw, I copy then trash that diskette.

> Back in 1990s the software package used to be carried by the usual FTP
> sites with DOS software, so I guess it still has to be available online
> somewhere.

Be aware that FDFORMAT is ALSO the name of Linux low-level formatter, AND
a Microsoft utility for formatting their 1.7M format.
JFORMAT (John Henderson of TallTree Systems) is another fun one to play 
with.

> I highly recommend it if you're still into the floppy business
> and don't use Linux.  The plain `format' command supplied with DOS gives
> you little control really and produces poor performance floppies.

My PCs (original 5150 and IBM 5160 being exceptions) can handle 1:1 , 
reading 9 sectors per revolution, making no need for interleave.
IBM and Microsoft were not UNAWARE of the concept of interleave.
But, many machines did need it, and most early hard disks, 
particularly on 5160, called for a a little experimenting based on how 
YOU used it, to determine YOUR optimum interleave.  (Programs that changed 
interleave for performance were sometimes unaware that the optimum one 
could be different based on what you were doing with the data)
WRONG interleave could result in needing more revolutions to read a track.

And, not all 3.5" drives do well with Mode3 ("NEC") format.

(I have used PCs with a few formats other than the usual ones)


--
Grumpy Ol' Fred     		cisin at xenosoft.com