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Whats the diff between /dev/sg0 And /dev/scd0 ??? scd0 is a block device whilst sg0 is a character device. Generically, block devices can be mounted and are cached, and char devices are for communication devices, aren't cached nor block aligned, and can't be mounted. Specifically, scd* (block) are for cdroms, providing the block access and commands for ejecting, closing, playing, etc. sd* (block) are for normal harddisks, providing partitions and some few commands. st* (char) are for tape devices (rewind, read, write, etc.). sg* are for the rest. They accept any scsi command you dare to construct, and so are used for controlling some esoteric devices or devices that have no standard interface. Scanners and recorders follow under this one (recorders, as they also relate to _reading_, have a corresponding scd* device). They can't be cached and need specific commands by vendor by action. /etc/fstab, as it relates to mounting filesystems, should refer only to block devices (or none, for virtual filesystems).
/dev/sg0 is a generics SCSI device, the one used by burning software to access the writing capabilities of your CD burner drive, using the ide-scsi layer driver. /dev/scd0 is the SCSI device used for CD-ROM accessing. What you experienced is how the ide-scsi module works. The kernel 2.6 does not need it any more. To find more about SCSI and SCSI generics please read /usr/src/linux-2.4.22-1.2188.nptl/Documentation/scsi.txt