[haiku-development] Re: r1a3 anyboot image too big for CD

  • From: "Michael Lotz" <mmlr@xxxxxxxx>
  • To: haiku-development@xxxxxxxxxxxxx
  • Date: Mon, 30 May 2011 21:21:41 +0200

> The anyboot image contain a partionning system. here is the partition 
> entry.
> 0x80, 0xff, 0xff, 0xff, 0xeb, 0xff, 0xff, 0xff, 0x00, 0x20, 0x00, 
> 0x00, 
> 0x00, 0x30, 0x07, 0x00,
> 
> We can see that the partition start at offset { 0x00, 0x20, 0x00, 
> 0x00, }= 
> 0x00000200 (little endian)
> So there are 8191*512 MiB lost between the end of the MBR and the 
> beginny of 
> the partition (~4MiB).
> IMHO, we don't need such a big alignment and then we could save a bit 
> of 
> space.

No.

The anyboot images aren't just relabled raw images. They are a 
carefully crafted hybrid between an MBR based disk image and an El-
Torito bootable ISO CD image. The part you are referring to is the El-
Torito boot part: a floppy image packed with the kernel and essential 
boot drivers to allow booting off a CD. The fact that El-Torito doesn't 
use the first few blocks is leveraged to also put an MBR inside this 
part. Both things combined this allows images to be burned to a CD or 
written to a USB stick or disk directly, essentially removing the need 
for a seperate CD and raw image for the different device types.

Regards
Michael

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