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Groups > alt.os.development > #8246

The BIOS Drive ID urban legend

From "Mike Gonta" <mikegonta@gmail.com>
Newsgroups alt.os.development
Subject The BIOS Drive ID urban legend
Date 2015-06-24 17:49 -0400
Organization Aioe.org NNTP Server
Message-ID <mmf8m0$tm3$1@speranza.aioe.org> (permalink)
References <8029ab57-0054-4410-aba8-d5189f025db7@googlegroups.com> <mm91hr$4lg$1@dont-email.me>

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"James Harris" wrote:

> Some BIOSes reportedly don't correctly pass the boot drive id
> in DL.

That is an "urban legend".

Some people probably observed that even recent MS boot loaders
don't use the BIOS returned "DL" but rather rely on the BPB
Drive ID. They probably inferred from this that the BIOS Drive
ID could not be relied upon. (This, in itself led to a lot of
USB booting difficulties for a lot of people and resulted in
the MBR urban legend).

The fact is that early MS-DOS ran on computers (before and
during the early IBM PC era) that had no BIOS. CP/M, 86DOS and
early MS-DOS came with OEM supplied BIOS on disk. The machine
itself only had minimal firmware code to load one specific
sector to a specific address and jump to it. That "boot sector"
then loaded some or all of the "BIOS" file. Even with the
latest version (Win98) io.sys, only four sectors were loaded.
io.sys then loaded the rest itself.

So, at that time, there was no Drive ID and of course only one
floppy drive attached to the computer - so not much need to
identify it. Backwards compatibility being the hallmark of MS.


Mike Gonta
look and see - many look but few see

http://mikegonta.com

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Thread

BootProg released "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-06-21 22:52 -0700
  Re: BootProg released "James Harris" <james.harris.1@gmail.com> - 2015-06-22 14:12 +0100
    The BIOS Drive ID urban legend "Mike Gonta" <mikegonta@gmail.com> - 2015-06-24 17:49 -0400
      Re: The BIOS Drive ID urban legend (was: BootProg released) "James Harris" <james.harris.1@gmail.com> - 2015-07-01 10:44 +0100
    Re: BootProg released "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-06-25 21:08 -0700
      Re: BootProg released "James Harris" <james.harris.1@gmail.com> - 2015-07-01 11:02 +0100
        Re: BootProg released "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-07-04 05:18 -0700
        Re: BootProg released "Kerr Mudd-John" <admin@127.0.0.1> - 2015-07-05 19:11 +0100
          Re: BootProg released "Kerr Mudd-John" <admin@127.0.0.1> - 2015-07-06 10:52 +0100
            Re: BootProg released "James Harris" <james.harris.1@gmail.com> - 2015-07-06 21:42 +0100

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