Memory Card Terminology Made Simple

SD, front and CF Memory Cards

Ever wonder what all that gibberish on the front of your memory cards mean.  With the help of Sandisk National Account Manager Peter Liebmann we’ll try to explain.

CF vs SD

Most cameras use either CompactFlash (CF) or Secure Digital (SD) cards.  Most cameras can only use only one type, although there are a handful of cards that have both a CF slot and a SD slot.


The most obvious difference between cards is capacity.  This translates directly into how many images your card can store. An 8-gigabyte (gig) card can hold approximately twice as many images as a 4-gig card.  There are many variables that will determine how big your image files are. Exactly how many images your card can hold will be dependent on the file format, resolution and level of compression applied to your files.  It’s mostly just common sense.  If your camera is producing 4 megabyte JPG files, a 4-gig card will hold slightly less than 1,000 images. (A gig is 1,000 megabytes).

Buying advice: Make sure you have enough memory cards on hand so that you are not forced to download images off your card until you are ready.  If you shoot Raw files, get big cards since the files are so much larger.  If you only shoot JPG files, I would suggest getting multiple 4 gig cards.  If you shoot Raw files, I would suggest getting multiple 8 and 16 gig cards.


You may see the read/write speed rating on a card expressed two different ways

A card labeled 60MB/s on it can read and write data at the rate of 60 megabytes per second.  This type of speed rating is generally considered to be the maximum rate at which the cards will write data.

You may also see another rating such as 400x.  There is a direct correlation between the MB/s number and the X number and they can be used interchangeably.  400X is equivalent to 60MB/s.  Expressed as an equation the MB/s number is divided by .15 to get the X rating.  So 60MBs(divided by).15= 400X. Conversely, 400x(times).15= 60

Buying advice: If you don’t shoot video, only shoot JPG,  and don’t shoot at rapid frame rates for extended periods of time (sports photography, birding, etc.), don’t worry about card speed.  If you shoot Raw or shoot video, get the faster cards.

Michael A. Schwarz is a commercial and editorial photographer, digital photography consultant and photo workshop leader based in Atlanta, Georgia.
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