Are CD/DVD-roms known to be quirky?

[no.to...@gmail.com]

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For years I avoided CDs, while I was waiting for the fad to pass.
Now my 3 PCs try to use an IDE CDrom and a usb-CD/DVD r/w,
which I can also unplug from its usb-interface to use as the
[original guts] IDE-device.

Often I need to re-try mounting before I succeed.
With 3 PCs and multiple versions of Linux and 2 CD-roms, moving
between PCs it's already confusing, without the apparent random
failure to mount.

Here's the latest trace:-
# mount /dev/hdd /mnt/cdrom ==
mount: block device /dev/hdd is write-protected, mounting read-only
mount: No medium found
-------------
A good readable CD was present.
This PC/CDrom combination worked last week.
Now it 'retracts the tray' for: `mount /dev/hdd /mnt/cdrom`,
which shows 'something'. But even for the previous CD which it was
reading last week, it won't mount.

And the other strange fact is that both:
eject /mnt/cdrom
and
eject /dev/hdd
work, so that somehow '/dev/hdd' IS associated with
'/mnt/cdrom' ?!?

==TIA.