Is there a way to determine what device was used to boot Linux?

e.g., when I boot normally on my system with two PATA drives, I boot off of /dev/hda, on my SATA system the boot device would be /dev/sda. And if I boot Knoppix/Slax/etc CD then my boot device would be /dev/hdc on the PATA system, or /dev/hda on the SATA box.

I've been nosing around in /proc trying to locate this info but haven't run into it yet. I thought I needed this info for some automatic mounting I was trying to do on boot from a Slax CD, but I found another way to accomplish that task. It's more of an academic question now. Just wondering.

Unlikely I would think. Hard enough to do in the simple case as I suspect no-one cares at early boot time.

Chainloading would toss all that in the bin anyway.

There is a simple and logical explanation to all these device names.

hda, hdb, hdc and hdd are IDE channels of primary master, primary slave, secondary master and secondary slave positions of the two IDE cables. IF you hook the CD rom to secondary master position then Knoppix will tell you the boot device is hdc.

You obviously have two IDE or PATA disks hooked to the primary IDE cable if they are called hda and hdb.

Sata is always named as sda although older distros may use hde.

Any of the above names can be pin-pointed to the exact location where the hard ware is connected to the mobo so no confusion at all. You only fool yourself but not Linux.

Thanks. I know how these things are referenced, I was attempting to write a script that would determine it for that script's own use, not my personal knowledge. I know which device I will be booted off of before I even start the boot process. But a script doesn't. My original "need" for this info was because I wanted to boot Slax and have it automatically mount the CD it booted off of, because I had other stuff on that CD (actually a DVD) besides the Slax installation. Big stuff, that wouldn't be appropriate for Slax's rootcopy scenerio. With multiple CD/DVD drives in my systems and some with SATA, some without, I wasn't sure how to identify the boot device. But this problem was solved much easier by adding the following to rc.slax:
How stupid of me. I was looking for /dev/hda, /dev/hdb, etc. when I could just reference it as /dev/cdrom. This references the first CD in the system, which is always the one I boot from.

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Maybe boot device isn't even determinable, like syg00 said. It's just an academic question at this point anyways.

p.s. - I was trying things like: "cd /boot; df ." which I thought kindof, mightof, couldof worked. For a harddisk boot maybe, but not when you're booting from a CD.

Thanks!