Yes, the card reader looks just like a removable thumb drive to the
computer. You can transfer files back and forth using Windows Explorer.
Mine is a Targus TGR-CDR25 and it has got to be the most useful computer
item I ever got for ten bucks. It has slots for four different kinds of
cards.

I think Garmin puts all its copy protection encryption in the file written
to the card. All the maps go in one big file and the GPS or Map Source
program then reads the unit ID numbers included in the file and compare them
with the hardware. I'll be very surprised if you don't find that you can
make as many backups as you want for the GPS(s) you are using or make back
up files on your computer disk that can then be used to make new cards
later. I'll bet you can't view the maps on your laptop though. Please let
me know if you can.

Since the cards can be easily written to, I'll bet that the first GPS you
insert them in writes it's unit number to the card and they won't thereafter
work in other units. You probably "registered" without realizing it.
Garming is putting us through all this to keep a hot gray market in copies
from developing.
--
Roger Long