[dba-Tech] Bootable CD

Can anyone tell me what defines a bootable CD? Back in the day, a bootable
floppy was created with the sys command, which copied command.com and
msdos.sys to the target, and you could then customize it with config.sys and
autoexec.bat.

The reason I'd like to know is that I still have a few 3.5 boot disks, but
no 3.5 drive. Assuming such a thing is made, I suppose I could get an
external 3.5" drive with a USB connection, but if there is an easy way to
create a bootable CD and then create some directories on it, maybe that
would get me where I want to go. For example, I downloaded several boot-sets
from bootdisk.com, but they are all set up with several 3.5" disk images.
Also I downloaded the new Google OS and copied its files to a CD but that
didn't work.

Any suggestions?

TIA,
Arthur