Another ID for HDD recognition, look in /dev/disk/ you find different ways to do so. UUID is unique for every HDD. Even if you change the HDD from disk 0 to disk 25 it's still recognized by Linux.
BUT NOT with the (hd0,0) form.
So if you change the HDD from master to slave or add one extra you only have to check for the (hd0,0) sentence.
The same happens to /etc/fstab where UUID resolves the changing of the HDD's
The newer versions of PCLos all use UUID
The same is the LABEL item that can be used on the same place as the Universally Unique Identifier.
With the old kernel from PCLos 2007 it did not work for my Grub menu.lst
Also with the old PCLos was the form /dev/hda5 instead of UUID=a1a74e10-9c73-418c-88e6-8659ede37838 in /dev/fstab
In this case you should also change the fstab settings, example, hda5 to hdb5
When you right click on the items in /dev/disk/by-uuid/ you see in the properties the connection with hda1, hdb2, etc.
So check carefully /boot/grub/menu.lst and /dev/fstab if you change or use strange settings in BIOS, or add or change the numbering of your HDD's.
Extra, SATA disks are called sda, sdb instead of hda, hdb, but not in the (hd0,0) sentence.
In my system I boot from SATA (sda) and have two IDE disks (hda and hdb)
SATA=hd0 IDE=hd1 and hd2
Also can boot (BIOS) from IDE
IDE=hd0 and hd1 SATA=hd2
When I do redo MBR (Sata as bootdisk) it always makes the wrong decision and put SATA as hd2 in menu.lst.
I found out the hard way