A:
The card has to be physically removed, but before removing the card, you have to virtually eject the card.
Go to the folder or drive that contains your photos or other data and right click on it. You should see an option "Eject". If you select that option, it digitally disconnects from the data, even though the card is still physically connected to the computer.
Using the "Eject" option like this prevents the data on your card from becoming corrupted when you physically pull the card out of the reader.