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Groups > alt.os.development > #8224

Re: BIOS limits on CD boot ?

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James Harris wrote:
...
 
> Strike that. Still without testing it but from further reading it seems 
> that for either type of emulation (floppy or hard disk) you would read 
> the emulated disk in 0.5k sectors - and probably via even the older BIOS 
> int 0x13-02 interface, but without emulation you would read in 2k 
> sectors - and via the extensions such as 0x13-42 and friends.

Thanks for all the checks and tests.

Now I think to understand that this emulation doesn't mean different CDs. 
 
> The El-Torito spec says that after booting with no emulation: "Once the 
> system jumps to segment:0, the program can retrieve its boot information 
> by issuing INT 13, Function 4B, AL=01. After the boot process has been 
> initiated the INT 13 Extensions (functions 41-48) will access the CD 
> using 800 byte sectors and the LBA address provided to INT 13 is an 
> absolute sector number. This gives any program running in no emulation 
> mode the ability to locate the boot catalog, and any other information 
> on the CD, without providing a device driver."

INT13_42 with 2K LBA-sectors sound as good news to me.
 
> That seems to say that the CD can be read (automatically using the most 
> up-to-date session) in 2k blocks using the BIOS extensions.
 
> I guess that the BIOS extensions would be present on any machine that 
> could boot from OD. If nothing else, an OD-interface card could add the 
> functions via a ROM. But such extensions may not be present on an older 
> PC when the OD is added purely as a read-only data drive.
 
> I have no idea how to access an OD from such a machine but MSCDEX and 
> similar may have done something like this. Based on some RBIL comments 
> about NWCDEX maybe such programs provided the int 0x2f-15 functions but 
> that doesn't explain how they would have read the ODs in the first 
> place.

They may read from CD the same way as I do, with the ATAPI-specified 
SCSI commands on IDE(SATA)-ports.

from your other post:

> To do that (untested) create an image with
>
>  mkisofs -r -J -c boot.catalog \
>      -b FILE_TO_BOOT -no-emul-boot \
>      -o /tmp/kesys1.iso FOLDER

I can't use this nor any other windoze/loonix tools.
So I have to study all the required header bits to create my own MKCD-
routines for bootable CDs of any kind.

__
wolfgang

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Thread

BIOS limits on CD boot ? "wolfgang kern" <nowhere@never.at> - 2015-06-19 13:44 +0200
  Re: BIOS limits on CD boot ? "James Harris" <james.harris.1@gmail.com> - 2015-06-19 14:15 +0100
    Re: BIOS limits on CD boot ? "wolfgang kern" <nowhere@never.at> - 2015-06-19 19:07 +0200
      Re: BIOS limits on CD boot ? Melzzzzz <mel@zzzzz.com> - 2015-06-19 19:22 +0200
        Re: BIOS limits on CD boot ? "wolfgang kern" <nowhere@never.at> - 2015-06-20 08:50 +0200
      Re: BIOS limits on CD boot ? "James Harris" <james.harris.1@gmail.com> - 2015-06-20 09:07 +0100
        Re: BIOS limits on CD boot ? "James Harris" <james.harris.1@gmail.com> - 2015-06-20 15:43 +0100
          Re: BIOS limits on CD boot ? "wolfgang kern" <nowhere@never.at> - 2015-06-21 06:10 +0200
            Re: BIOS limits on CD boot ? "James Harris" <james.harris.1@gmail.com> - 2015-06-21 18:13 +0100
              Re: BIOS limits on CD boot ? "wolfgang kern" <nowhere@never.at> - 2015-06-22 09:55 +0200
                Re: BIOS limits on CD boot ? "James Harris" <james.harris.1@gmail.com> - 2015-06-22 12:04 +0100
                Re: BIOS limits on CD boot ? "wolfgang kern" <nowhere@never.at> - 2015-06-30 20:03 +0200
                Re: BIOS limits on CD boot ? "James Harris" <james.harris.1@gmail.com> - 2015-07-01 11:19 +0100
  Re: BIOS limits on CD boot ? "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-06-19 10:56 -0700
    Re: BIOS limits on CD boot ? "wolfgang kern" <nowhere@never.at> - 2015-06-20 08:55 +0200
  Re: BIOS limits on CD boot ? "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-06-19 18:15 -0400
    Re: BIOS limits on CD boot ? "wolfgang kern" <nowhere@never.at> - 2015-06-20 09:18 +0200
      Re: BIOS limits on CD boot ? "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-06-20 07:43 -0700
  Re: BIOS limits on CD boot ? "wolfgang kern" <nowhere@never.at> - 2015-06-21 16:04 +0200
    Re: BIOS limits on CD boot ? "James Harris" <james.harris.1@gmail.com> - 2015-06-22 12:13 +0100

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