R: Re: 3.5 floppy imaging

[Maciej W. Rozycki]

On Sun, 17 May 2015, Fred Cisin wrote:

> > The only reason I guess is that they're bootable disks. Otherwise a simple
> > filecopy is more than enough :)
> 
> If they are bootable DOS disks (and normal, not weird), then there is one part
> that won't come across with a filecopy.  That is Track 0, side A, sector 1. If
> they are some version of DOS for which you don't have a copy of the
> boot-sector, that might be worth saving. Using DEBUG, you can copy that into
> RAM, and save it as a 512 byte file.

 Why bother?  As most people suggest `dd' is the most straightforward way, 
and on a reasonable OS you can then mount the filesystem directly from 
such an image of a floppy via a loop device.  You can then copy individual 
files out from there if really needed.  You can copy the boot sector 
separately with `dd' too if required, also from that image rather than the 
original.

 With defect-free media, which is usually the case with properly stored 
diskettes made up to mid 1990s, in addition to what has already been 
written I'd suggest the block size of 32768 with `dd' to get a decent read 
performance.  The performance of individual floppies may vary depending on 
how they have been formatted, i.e. if any sector staggering has been used.

 Also, from experience, with marginal media you may still be able to read 
data out eventually with a linear dump such as `dd' performs, while 
copying files out individually that involves random seeks may not be as 
successful.

  Maciej