>> (The real need is to fix a Windows box that won't boot, and I intend
   >> to do it by cloning the disk from another box that is fine.  [...])

   > This often won't work because FAT filesystems change shape depending
   > on the disk's c/h/s geometry, so it's conceptually impossible to copy
   > one from one disk to another without understanding the filesystem,
   > unless both disks are of identical geometry.

   I wouldn't even consider this unless the disks were identical.  (So far
   I haven't investigated in detail, but the machines are part of a pile
   of about two dozen all bought together that are at least supposed to be
   all identical.)

Actually, some ways of moving files around work just fine despite
non-identical disks.  For example, the following works fine in my
experience when you can mount the disk/partition under NetBSD
(including using the install floppy and a network to do this for a
FAT-only system):

- create a tarball of your good FAT disk

- create an empty FAT filesystem on your target disk with appropriate
  geometry

- untar the tarball on the target disk

I've been revamping the newfs_msdos tools to make the second step a
straightforward process for any (i.e., not just floppy disk) FAT12/16
disk or partition (FAT32 will be later); stay tuned.

Cheers,
Brook