Should I format in the camera or computer?

These days I don't think either is a likely cause of card corruption, but you should always format cards in the camera whenever possible because some manufacturers interpret small aspects of the way data is placed on a drive differently. 

Here's what you should avoid if you want to avoid card corruption: 

  1. Shooting bursts of frames with too slow a card for the camera
  2. Shooting right to the point where the card is filled (especially in bursts)
  3. Deleting images on the card, particularly when the card is full, and then doing #2
  4. Shooting video until the card is full. 
  5. Swapping cards between cameras.

#1 has a tendency to cause the write controller in the camera to get stressed and miss a beat. 

#2 is even trickier because of the way card space is calculated on the fly by the camera. 

#3 sort of is the worst of all evils: the aspects of #2 still apply, and you're probably fragmenting data areas on the card in doing #3. The combination can be deadly, particularly with—you guessed it—slow cards shot in bursts (#1). 

#4 is problematic because video compression is being done by the camera in real time, and sometimes there's less space left than the camera thought when it decides it had better save what it's got to the card and stop the video recording.

#5 gets back to that “some manufacturers interpret small aspects of the way data is placed on a drive differently.” Normally, swapping between cameras should just create a new folder within the DCIM folder, but sometimes there are small changes in the FAT or directory table that can be problematic.

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