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Re: The BIOS Drive ID urban legend (was: BootProg released)

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"Mike Gonta" <mikegonta@gmail.com> wrote in message 
news:mmf8m0$tm3$1@speranza.aioe.org...
> "James Harris" wrote:
>
>> Some BIOSes reportedly don't correctly pass the boot drive id
>> in DL.
>
> That is an "urban legend".

That would be very welcome, if true. But how do you know that it being 
an urban legend is not itself an urban legend? For example, SYSLINUX 
includes code to support machines which fail to pass the boot drive in 
DL. Are you saying that such code is pointless? If so why was it 
included?

> 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.

Interesting. From the few releavant hard disk tests I have run I have 
seen the BIOS assign 0x80 to the boot drive regardless of which disk it 
booted from.

> 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).

I suspected that the problem was buggy old BIOSes rather than anything 
new - but that was purely because newer BIOSes would/should have fixed 
such bugs.

> 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.

OK. That could be the issue.

> 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.

OK.

James

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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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