What happens when you boot from CD (exactly)? hardware gurus.

[AlGood]

When the CDROM is in the boot sequence, what is going on exactly?
What makes a CDROM bootable, exactly? Where does the system get the drivers to even access the CDROM?
What steps does the BIOS take when boot from cd is enabled?
thanks.

 

[Soccerman]

well I don't know for sure how the BIOS can access the CDROM right away (maybe like DOS, it needs to load one driver into memory to read from most CDROMs), but as far as I know, bootable CD's actually emulate floppy drives when loading.. at least, the bootable Linux CD's I have do something like that.

most likely the BIOS has a set of generic drivers for it's own mini OS (after all part of the word BIOS is input/output) to read the CDROM, it's just a question of what the files on the bootable CD when they are run (remember, they don't have to be DOS, Unix, or Windows files, as long as they're compatible with x86 they'll run).

 

[MallowJr]

It's also kind of hard to make a bootable CD, anyone have programs out there to let me burna bootable CD?
It might be better instead of just using the win98se cd I have and quitting to DOS ....

 

[ObiDon]

You can use nero 5+ to make a bootable CD. It's pretty easy once you have a working boot floppy. You can even add extra files onto the non-floppy image portion of the boot CD. Just remember to make sure that you have CD-ROM drivers on your boot floppy or else you will only be able to access the A: portion of your CD after you boot :Q
Say you have one CD drive and one hard drive with a single large partition...after you boot you will have an A: drive for your boot CDs image, a C: drive for your hard drive, and a D: drive for all the extra stuff you put on your boot CD. Pretty cool once you have it all set up

 

[burtrom]

When you boot from CD it is looking for files on the CD which contain the drivers and other data. Usually they are .bin files. You can very easily use Easy CD Creator 4 or 5 and "create a bootable CD". It will want a bootable floppy disk to copy the information from. The only problem is that you are limited to 1.4 mb on the bootable image. You will need to make sure that the floppy you use is one that has CD-Rom drivers. I usually use a modified version of a Windows 98 SE boot disk. I kill the RAM drive and only load what I needs to. It has drivers for SCSI and IDE CD-ROMS. I also throw utilities like FORMAT and FDISK in so that I can do pretty much what ever I need. I also load SMARTDRV. It speeds things up a bit.

I have also used CDRWIN to make a bootable disc. You are not limited to 1.4 mb but it is a LOT harder to make the .bin file.

Hope this helps.

 

[interchange]

Modern BIOS's have support for ATAPI tape/cd-rom standard, so just about all CD drives will be able to be bootable just like any other drive; the bios has no effect on assigning a letter -- that's a dos thing, and other OS's don't assign letters. It's just that the BIOS knows how to assign the proper resources and boot from the drive.