okay, that explains it. it is for the extra stuff like that preformatted partition. i´ve seen that with USB sticks, too.
That pre-formatted partition has different block size (2048 as opposed to 512) and is treated as CD image!
Information, how many sectors at the end of the drive should be reserved for the CD image, resides in WD MyBook firmware and is transparent to formatters, no matter what hard drive you connect to controller board - non WD, blank, SSDs etc.
Commands to mount this CD image are also in firmware and OSes will always attempt to do so, even if the drive is blank i.e. all zeroes.
WD drive lock/unlock etc. software is copied to those CD image sectors during manufacture and can only be run from there.
What's worse, that damned CD image takes away some disk space. I have WD MyBook Studio model 111D (aluminium enclosure) where CD partition is around 30MB, but, the one that OS923 has - 1112 takes away around 800MB and that's significant
How do I know that? I flashed 1112 firmware to my 111D just for kicks and found it out.
They both have the same Oxford OXUF943 chip.