Groups > comp.os.msdos.programmer > #3930

testing "USB-ZIP" images in an emulated environment

From	Mateusz Viste <mateusz@xyz.invalid>
Newsgroups	comp.os.msdos.programmer
Subject	testing "USB-ZIP" images in an emulated environment
Date	2021-03-17 10:08 +0100
Organization	. . .
Message-ID	<20210317100856.5fc475f5@mateusz> (permalink)

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Hello fellow programmers,

I am fiddling a little bit with building a bootable USB image with DOS
on it. So far I learned that there are 3 modes of USB booting:

* USB-HDD: the most common it seems, where the BIOS uses USB storage to
emulate a normal hard disk (DL=0x80 at boot time). The USB drive must
have a proper MBR for this to work, once booted under DOS the drive
appears as "C:". I was able to test this one on my laptop and it works.

* USB-FDD: as far as I understand, this works by simply writing a floppy
image to the USB device, ie. no MBR, only the FAT12 fs is present on
the USB drive. Some obscure sources say that for this mode to work, the
USB drive should present itself with a name that hints as a floppy
vendor... I don't have any way of testing this so I can only wonder.

* USB-ZIP: emulated ZIP-100 or ZIP-250 drive. Requires a specially
crafted MBR where only partition 4 is being used and its CHS geometry
must mimic an actual ZIP drive (64 heads, 32 sectors, 96 cylinders). It
would seem (?) that in this mode, the BIOS skips the MBR bootstrap and
loads the VBR right away. Once booted to DOS, the drive is epxected to
appear as "A:" (ie. DL=0).

Now my problem is much more practical: none of the PCs I have support
booting in either USB-ZIP nor USB-FDD modes, so I wonder how I could
test it.

Any idea how these modes (esp. USB-ZIP, as that's the one I am most
interested in) could be tested in a virtualized environment? I have read
the QEMU manual but did not find anything that would hint at QEMU
providing support for such USB booting. Did anyone here investigate
this subject in the past already? Any hints welcome!

Mateusz

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testing "USB-ZIP" images in an emulated environment Mateusz Viste <mateusz@xyz.invalid> - 2021-03-17 10:08 +0100
  Re: testing "USB-ZIP" images in an emulated environment JJ <jj4public@gmail.com> - 2021-03-18 02:40 +0700
  Re: testing "USB-ZIP" images in an emulated environment Rod Pemberton <nomailings@trgzxcqvbe.cpm> - 2021-03-18 19:04 -0500

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