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Good CD/CDRW/DVD/DVD-+RW boot faq


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Can anyone provide a quick, concise, explanation of how a CD-ROM or DVD-ROM reader or writer, requests and discerns boot information/media descriptor info from all the various CD-DVD bootable formats.

How many different media are rocognized as bootable? How do the boot sector differ?

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To put it simply....

The bootsector is just that...a spot on the DVD/CD at a certain location.

In reality, the TOC (Table of Contents of the disc) tells that there IS a boot sector and where it's located. I believe via specification, it's within the first 100 blocks, but you'll have to look up the El Torito boot spec.

For a CD to be considered a CD, it HAS to conform to the CD spec, same as DVD. Which means if it does NOT conform, it doesn't get that cool little logo on the disc. Different media does not affect bootablity. Readers don't either. User and BIOS do.

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Thanks, maybe I'll get around to making one of multi-boot dealies.

prathapml - I'm sure you have the knowledge to hand off a couple of lines that would make sense to dummies that don't want "rtfm". I'll root through your stuff, obviously when you get around fooling with a hex editor on a sector of disk, you might say "you know what's going on".....

A few years back I did read a couple of "RFC" type docs on how BIOS makers had to write the code to hand-off and prioritize possible boot devices. (and how boot devices had to supply a paramter to "idenitfy" themselves. (boot status)

All I wanted was a 50,000ft view of what happens when a given type of optical device is given the "go" and starts munching around the media it detects by it's BIOS.

Is it "booktype" > bootsector > TOC ?

Bootsector/leadin? > booktype > TOC ?

Is there such a thing as a leadin-file? Is there a data structure on all media that emulates an "io.sys" .... or "disk translation" code....?

Sorry, if this off-topic, I just wanted the big picture?

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I believe it's more....


The leading has a bit that signals it's bootable, and the TOC tells where it is on the disc.

As for the emulation of the IO.SYS, it's not really neccesary. IO.SYS was used because it was a DOS subsystem. the CDROM boots whatever it needs to. Like the XP CDs, but into the ntloader which then starts setup. Linux boots something, then starts the kernel.

the CD's bootcode and what to look for, IS the bootsector. Which is why the bootsector has to have a spec, so it's all compatible across systems.

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