CD File Reading

JoeTheProgrammer · Post by **JoeTheProgrammer** » Thu May 29, 2008 3:41 pm

How does an operating system live cd when booted read files from the cd? Does it use an internal atapi driver of some sort or what are other ways that the cd can be read from in protected mode?

Thanks,
Joseph

svdmeer · Post by **svdmeer** » Thu May 29, 2008 4:00 pm

For booting El Torito, http://en.wikipedia.org/wiki/El_Torito_ ... tandard%29

After booting, a hardware driver for accessing sectors (for example scsi or atapi) on the CD and support for a CD filesystem (mostly ISO9660).

Combuster · Post by **Combuster** » Thu May 29, 2008 4:13 pm

Read the wiki: Bootable CD

JoeTheProgrammer · Post by **JoeTheProgrammer** » Thu May 29, 2008 4:16 pm

Combuster wrote:Read the wiki: Bootable CD

I mean after the cd boots with grub and executes my kernel, how does the kernel read files on the cd?

Combuster · Post by **Combuster** » Thu May 29, 2008 4:25 pm

Well, at that point you'll need ATAPI drivers and filesystem support.
But since you use GRUB, you can also load a ramdisk into memory and use that

JoeTheProgrammer · Post by **JoeTheProgrammer** » Thu May 29, 2008 4:26 pm

Ok, thanks for your help.

Joseph

robos · Post by **robos** » Thu May 29, 2008 4:43 pm

My memory is a bit fuzzy on the subject, but if you can stay inside 1.44 MB (size of a floppy) then you can put whatever you want in that floppy image and it will be accessible through the floppy emulation the BIOS is doing for you when you boot from it. So you can easily put extra stuff in the additional "sectors" and load that whether you put a fat file system in there or not.

Obviously the rest of the CD/DVD is still ISO / UDF and to get to that you will need a driver I'd imagine. But you have 1.44 MB of space to put that driver in

I think the above is correct... if someone knows it isn't don't hesitate to correct me!