They're a multi-format memory card reader. You probably have one in your PC or your monitor.
Hmm, I don't think I have one in the pc (definately not the old one) but I am sharing the monitor through a switch while making this move. I don't think the monitor has such an option, though it could have. I wonder if the new computer could be reading the drives from the monitor somehow? But if that was the case, it seems that explorer would show them too. Looks like it is just something I will have to live with.
Explorer won't show them because they are empty. The same as Opus doesn't show them in the Drive Buttons toolbar after adding the "hideempty" argument.
Opus 9 doesn't have the ability to hide empty drives in the folder tree or My Computer (it only has it for the Drive Buttons toolbar), but that is coming...
I have a memory card drive on my printer, which I forgot all about, and spent a happy morning puzzling over... 
Godelpus. Another thing to remember.
This reminded me that I have one of those on my Canon printer.
Fortunately, it is usually invisible in Opus thanks to:
Go DRIVEBUTTONS=cdrom,network,removable,hideempty
Never used the card reader. Guess it will always remain invisible.
Maybe I should see if it even works!