Date   : Sun, 29 Mar 2009 11:02:24 +0100
From   : philb@... (Phil Blundell)
Subject: Omniflop

On Sun, 2009-03-29 at 10:31 +0100, Alex Taylor wrote:
> 2009/3/29 Jonathan Graham Harston <jgh@...>:
> > Unfortunately, as is common in the brain-dead, strip down all
> > functionality to make it dirt cheap, PC world, USB external floppy
> > drives translate all access commands from the computer into
> > accesses to DOS formatted disk systems.
> 
> That can't be entirely true, because I've often used a Toshiba-branded
> USB floppy drive on various Macs to read and write HFS-format disks,
> including reading and writing images with Apple's Disk Utility. I've
> got a pile of them at work, they came with Toshiba Satellite A10
> laptops from about 2003. I think they're actually made by Y-E Data.

It's true that, like all USB mass storage devices, USB floppies use the
SCSI direct-access command set for reading and writing, and it's also
true that this command set operates on logical block addresses rather
than physical head/cylinder/sector addresses, with the controller being
responsible for doing the translation.  That does mean that you lose
some of the flexibility of a host-bus-interfaced controller, though it
seems a bit harsh to characterise it as "dirt-cheap" and "brain-dead":
you could make exactly the same argument about SCSI or IDE hard disks
compared to ST506.

(In theory it would be possible for a USB floppy drive to provide
vendor-specific commands to give you lower-level control of the sector
layout.  I've no idea whether any of them actually do, but the
controller IC datasheets would presumably reveal the truth.)

So, assuming you meant 1.44M HFS floppies, these would work fine because
the physical layout of sectors on the disk is the same as that used with
DOS.  The controller doesn't have any knowledge of the high-level
filesystem format being used on the disk; it could equally well be DOS,
or HFS, or ADFS.

p.