Erasing Images vs. Formatting

This is my understanding of what happens.

Deleting a file removes its entry from the directory structure and frees up its storage segments so that other data can be written into it. That's all it does. If you don't put any other data on the card, the image is still there. You just can't reach it through the operating system. However, low level disk access routines can reach it. That's what recovery programs do.

Formatting wipes the entire directory structure and starts fresh. It does not delete the data associated with the files. I don't think either type of formatting actually wipes the memory. That's how the FBI sometimes can gather evidence on hackers. There are programs that will wipe memory. But you don't really need them if all you're using your cards for is photography.

When the operating system writes data to the card, it puts it in available segments. When you reformat, all the segments become available in sequence. If you delete one file, but don't delete all of them, you can get fragmented segments. So pieces of subsequent image files might be in several different places in memory. Theoretically this shouldn't matter, except that it might have an impact on read and write time. The idea of having fragmented files bothers me as I'm not convinced that the operating system is always perfect. So I reformat whenever I put a new card in the camera.

I have been asked to recover images from cards that have gotten corrupted when they were used in several different Canon camera models without reformatting. They were swapped repeatedly between xxD and xD models. Some people tell me that this is impossible, but I've had the cards in hand.

Delete/erase is what I do in the field when an image isn't a keeper for whatever reason (OOF, bad exposure, etc.). Format is what I do each time after I've downloaded the images to my computer and put the card back into the camera. Re-insert, format, voila - a "clean" card ready for the next shoot.

joedlh wrote in post #13554766
When the operating system writes data to the card, it puts it in available segments. When you reformat, all the segments become available in sequence. If you delete one file, but don't delete all of them, you can get fragmented segments. So pieces of subsequent image files might be in several different places in memory. Theoretically this shouldn't matter, except that it might have an impact on read and write time. The idea of having fragmented files bothers me as I'm not convinced that the operating system is always perfect. So I reformat whenever I put a new card in the camera.

This description is correct for ordinary, magnetic, hard drives. But it's totally the opposite for solid-state memory (like SSDs and CF/SD cards) where the data is always fragmented. These devices can only write/erase data a limited number of times (don't worry, it'll take you decades to reach that limit). To avoid the same bits of memory always getting used, and wearing out quickly, the devices have firmware in their controllers that spread the data out across all memory locations - it deliberately fragments your files!

It can do this quite happily because file fragmentation has virtually zero impact on read/write speeds. With mechanical hard drives file fragmentation is a problem because it takes quite a long time (several milliseconds) for the read/write head to move to a difference location on the disk platters. If a file isn't fragmented then its data is stored in adjacent areas and there's very little time lost. If it's badly fragmented then the head is zipping about all over the place. But solid-state can read sectors 1,245,3,967,88 just as quickly as it can read sectors 1,2,3,4,5.

Most of the time I delete the images on the PC right after transferring. Then I occasionally will format in camera later.
I do this for one reason. When shooting an event and quickly changing cards I do not want to place a card in that was not already cleared out. Then end up only shooting a short amount of time and card is full.

I'm a formatter. I get it off the card, make sure I have a backup, and format before using.

What Frank Hollis said is correct. On a flash card, fragmentation makes no difference. (That's a slight lie; I can tell you a procedure that would make a slight difference in performance. You'll never do it unintentionally.)

If your card is less than 50% full, "Erase All" might result in a TINY improvement in your card's lifetime. But the emphasis is on "tiny". Randomness will make a much bigger difference.

I always format, not because one way is better than the other, but because I have to wade through fewer confirmation prompts. I taught my wife to always "Erase All" because it doesn't delete protected pictures, and the first shot on her camera is of her business card in case it gets lost.

I format, and I always do it in the camera (not on the PC). I have heard of rare cases where formatting the card on the PC causes issues with some cameras.

gkuenning wrote in post #13577114
I taught my wife to always "Erase All" because it doesn't delete protected pictures, and the first shot on her camera is of her business card in case it gets lost.

That's pretty genious. As long as you happen to get an honest person as the finder.