To improve the overall performance of a memory card, format it occasionally in your camera, not your computer.
Erasing images from a memory card is fine but occasionally it needs to be formatted, or initialized as some digital camera manufacturers refer to it. There are those who insist that formatting isn’t necessary and never format their cards. They are wrong.
To clarify the matter, I contacted Sandisk, the world’s largest supplier of flash memory cards. According to a SanDisk technical support specialist:
There are two methods to erase the images that are stored on your memory card.
Using the camera’s menu to ‘format’ removes all files and sets up the memory card for use in the camera. ‘Delete’ (ie. erase) on the other hand removes one image after another. Therefore, it is a good idea to occasionally format a memory card (in the camera and not on a computer). Delete the images if you wish to cleanup the memory card daily.
Formatting helps clear the card of extraneous issues from standard use. Erasing images just tells your camera that it’s okay to write over the images already on your card. So you will not actually remove images, but just take images over the existing ones. This always leaves ‘traces’ of data on the card. By formatting it you actually remove the images before taking new ones. So you will start of with a fresh data free card.
Back up images before formatting
Recovering images after a card is formatted may not be possible, so use this function prudently. Before erasing or formatting a memory card, make sure to transfer all image files to your hard drive or other back-up device.
For those who don’t take a lot of pictures, formatting your memory cards a few times a year should suffice. Do it more often if you shoot a lot of photos and video, or if you’re having issues with a card.
Format a memory card in camera not computer
Please take note that SanDisk recommends formatting memory cards used for photography in your camera, not a computer. Remember, any photos you have “protected” on the card will be deleted during the formatting process. Protected images will not be erased when you use the Erase function,
TIP: When you get a new memory card, format it before using it for the first time.