I am going through the linuxrc on KNOPPIX and want to understand how it works.

I noticed that the ramdisk(thus the root /) is created on /dev/shm but at the end of the script, it transfer the root system to /dev/ram0 through

echo "0x100" > /proc/sys/kernel/real-root-dev

(where 0x100 is the major-minor device id for /dev/ram0). Is this a kernel feature that is builtin to linux ? I failed to find any node under /dev for /dev/shm which I assumed is not needed like other devices say /dev/hda1...

thanks for any help in advance.
EDIT: Forget the above, I was dead wrong in understanding the code, now I know better after further reading.