Originally Posted by R_Fredrick_Smith
Always format in the camera. When you format in the computer it often just does a quick format and this leaves the files there, and just updates the fat table. Thus if some problem occurs, you can end up with photos garbled, etc. The camera format is clean and is optimized for the camera's use.
I won't disagree with formatting in camera, but if anyone thinks that the camera does any more error checking than a quick format in the computer, you're kidding yourself. Count the time it takes from when you hit format, until it's ready to shoot, then divide that by the size of the card. If it's anywhere near the read (let alone write) speed of the card, then maybe it's checking for bad sectors. Truth be told that embedded into the firmware of the camera is FAT code that most likely originated in a commercial OS and was ported to the camera processor. I do this for a living (not with cameras, but other embedded systems) and nobody re-writes this code from scratch. Too hard to test, so you buy the library source and port it.
It may write some other data to the card, but it is not doing any more checking than the format utility does.