I have a program, mbr, which can print the mbr of a physical disk number. this
would allow you to see a report of the MBR of the disk (up to 4 partitions),
and examine a BIOS or windows disk number. it is available for both windows
and dos.
I find that the bios disk number 0 and the windows' \\.\PhysicalDrive0 match
exactly, 1 matches too, etc.
Jim Michaels
>________________________________
> From: Bernd Blaauw <[email protected]>
>To: [email protected]
>Sent: Wednesday, March 21, 2012 1:32 PM
>Subject: Re: [Freedos-devel] Insight requested on drive letter assignation in
>DOS
>
>Op 21-3-2012 20:53, Travis Siegel schreef:
>> I'm not a dos boot expert, but my understanding was that dos assigns
>> drive letters, so if you're the boot manager, you should be able to
>> install drives any letter you like, regardless of where they fall in
>> the actual boot chain. I've seen programs from time to time that did
>> fiddle with boot sequence (such as boot around) but it required a
>> valid floppy in drive a that it could patch to force boot from
>> another drive.
>
>GRUB/GRUB4DOS seem to have all kinds of ways to map drives almost anyway
>you like.
>
>
>> However, if you're the controlling process at boot time, I see no
>> reason why you couldn't assign any device of your choice to drive C:
>> whether it's the first hd or the third usb stick, but again, I'm no
>> expert in dos boot code, so I could be completely wrong here, but
>> since dos must get it's boot sequence from somewhere, and device
>> assignment happens in the kernel (not in bios) you shouldn't have
>> trouble assigning any letter you like.
>
>
>
>> I know bios assigns the boot sequence, but afaik, it does not dictate
>> drive letter assignments after that point.
>
>BIOS typically assigns 0x00 to the floppydrive you booted from, and 0x80
>to the drive you booted from. Some bootloaders and bootprocedures can
>shift this a little bit, like the El-Torito disk emulation modes
>implementing int13 and thus pushing physical storage drives a bit
>further ( floppy becomes 0x01 when using floppy emulation, harddisk
>becomes 0x81 when using harddisk emulation).
>
>The DOS kernel is responsible for mapping partitions (with a recognised
>filesystem, thus only various versions of FAT) to driveletters. Multiple
>disks and partitioning scheme (MBR, primary partitions and logical
>partitions) come into play here as well.
>
>As the FreeDOS kernel can be modified, I guess you can alter:
>* bootsector if needed (0x81 if you insist though 0x80 should do)
>* drive assignment in kernel (start at D: but allow C: afterwards?)
>* search for \(FD)CONFIG.SYS on same partition (filesystem) as the
>kernel is located instead of A:\(FD)CONFIG.SYS or C:\(FD)CONFIG.SYS
>* same for COMMAND.COM (if no CONFIG.SYS or no SHELL(HIGH)= line) and
>AUTOEXEC.BAT (same reasons) I guess.
>
>The simple way is trying above with floppy first, with first floppydrive
>getting B: assigned instead of A:.
>Do note that lots of scripts expect A: or C: though.
>
>Bernd
>
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