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Re: BIOS limits on CD boot ?

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"wolfgang kern" <nowhere@never.at> wrote in message 
news:mm0vas$t3l$1@speranza.aioe.org...
> Let's assume a bootable OS on an ISO 9660 conform CD/DVD.
>
> How many bytes can the BIOS load from such media ?

I take it you are thinking to have an optical disc boot sector and use 
it to load code from further on in the disc. Which BIOS function were 
you thinking of using and were you thinking to use emulation (floppy or 
hard disk) or native mode?

Int 0x13-42, if supported by all BIOSes you want to run on, looks as 
though it could read as far as you could want into the optical disc 
though I am not sure whether or how it would cope with 2k sectors if you 
used native mode rather than an emulation.

> As I figured some time ago, INT13_42 can't load above 1.MB, but if the 
> BIOS can load 500K to 0x08000... that would be enough for me yet and 
> it could save me from temporary installing my CD-reader for the boot.

A small point but I think the 2k boot record gets loaded to 0x7c00 
(meaning it would end at 0x83ff) so you wouldn't be able to read the 
rest of your code to 0x8000. Info from the first of these useful links.

  http://wiki.osdev.org/El-Torito
  http://wiki.osdev.org/ISO_9660
  http://wiki.osdev.org/Bootable_CD

Either way, once some code has been loaded you could always copy it 
above 1Mbyte and then load more if you needed it, couldn't you? That may 
mean you could load as much as you want.

> So I ask here before I burn several CDs to check if this work.

I haven't tried it but it looks as though you could boot from an 
optical-disc *image* using an emulator. For example, Oracle VirtualBox 
has a boot-from-cd-image option. That would save you burning throuh 
multiple CDs. :-)

James

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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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