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Re: BIOS limits on CD boot ?

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James Harris replied:

>> 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?

I thought about reads by INT13 without any emulation.
 
> 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.

I may rely on 2K sectors, but would the BIOS understand the LBA-numbers ?  
 
>> 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.

wouldn't the BIOS only load the first 512 bytes to 07c00 ?
 
>  http://wiki.osdev.org/El-Torito
>  http://wiki.osdev.org/ISO_9660
>  http://wiki.osdev.org/Bootable_CD

Thanks, I copied and read this. But I cant/wont use GRUB or similar.
 
> 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.

Yes, this is possible anyway.
 
>> 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. :-)

Not sure yet if this emulation is something I could do myself.

I can't use anything from third parties inbetween powerup and CD-boot 
because my clients wont pay me for the work of others.

__
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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