Mail Archives: opendos/2000/10/29/21:26:35
> > > > BTW, I lost the message with the information about what should be in
> > > > the OEM signature to be MS-DOS compatible. Can someone please
> > > > resend it to me? :)
> > > In retrospec of this paragraph that I am replying to now, I am at a
loss
> > as
> > > to WHAT signature you want.
> > The OEM label, found in every DOS boot sector. DOS boot sectors are
laid
> > out thus:
> Thus, I
> do not know what signature you are asking about. both of these and the OEM
> ID are signatures.
Well, the original poster asks about the OEM signature, so wouldn't it be
reasonable to assume they meant the OEM label?
The problem with the FDISK release being referred to is that it changes this
from IBM 3.3 and then picks incorrect values for cluster sizes etc. It's
one version of FDISK affected - that in 7.03 as I recall (I use 7.02b2
myself) - so it's not a problem across the whole DR-DOS version spectrum.
> > media' otherwise. Also, before DOS v3, the loader used the BIOS's BPB
> > rather than the one on the disk, so some DOS v2 issues didn't fill in
the
> > BPB - these diskettes are unreadable on DOS 3 and up.
>
> Are you saying that DOS 3.0 and later cannot read diskettes formatted with
> earlier DOS?
I'm saying some v2 issues created floppies that cannot be read (or maybe
just booted from) in v3+.
> If so, that is not true. I can still read and have been able to
> read those 160K single sided 5-1/4" floppies formatted with DOS 1.0 and
DOS
> 1.1.
I'm not sure is DOS 1 kept a BPB in the boot sector at all - but certainly
DOS 3 was the first version in which any use of the disk-based BPB was made
(previously, a default table was used). With DOS 3, OEMs were forced to lay
the boot sector out properly - previously, some OEMs didn't bother with a
BPB.
> I have even seen floppies with that area (BPB) totally corrupted and
> still read the diskettes.
Perhaps it's just the boot sector code that makes use of the BPB then. Was
the media descriptor correct? ISTR DOS can work out what to do with most
diskettes just based on the media descriptor, as long as nothing's been done
to the format.
About NT's DOS support - it's been a while since I looked at NT properly
(swapped the disk out to install NetWare, can't remember which disk it was
on), but I guess there's an MS-DOD compatibility layer in there somewhere
(similar to Win3+'s WINOLDAP) which is providing all the DOS services that
can be provided safely - most (if not all) of INT 21h, 2Fh, INT 20h and all
the others. (There's obviously a compatibility layer to provide INT 10h
video services and INT 16h keyboard routines, and probably INT 13h disk
access with some bits trapped). Then MS simply take the standard DOS utility
source (from DOS 5 or 6 I guess), change the version information it expects,
alter some messages and there we go. The alternative is that the whole
shebang is made up of Win32 app(let)s.
Regards,
Ben A L Jemmett.
(http://web.ukonline.co.uk/ben.jemmett/, http://www.deltasoft.com/)
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