What actually happens when a user reboots his or her system with an OS disk (or other bootable disk) in the CD/DVD drive?
For example, when I put in my OS installation CD and start the computer up, it says "Press any key to continue from CD or DVD...". How this is done on the actual CD/DVD? Because this indicates that when each time CPU is rebooted it first checks the CD drive…
Now my question is, how does a CD/DVD put these contents on it to indicate that it is a normal disk versus a bootable/OS disk? How does the computer identify such discs on boot?
Best Answer
The El Torito CD-ROM standard is an extension to the ISO-9660 spec that allows booting from CD. Some OS installation cds, Windows is one example, use these extensions to make installing an operating system easier for the user. Your computer is probably configured to check the CD-ROM drive each time the system boots for a bootable CD. Many CD burning applications have options to burn CDs using the El Torito specification.
In the case of a Windows installation disc, it may require you to hit a key to boot from the cd, otherwise it will try to boot from your hard drive instead. You can change the boot behavior of your system by going into the BIOS. It is possible to make a change to your system in your computer's BIOS that will render it unbootable. Most likely this can be repaired easily, but may cause less-knowledgable users a little trouble to recover.