Following our multi-part discussion of flash memory cards for cameras kicked off by Ctein last Wednesday, I've been seeking a reasonably authoritative answer to the question "Should you 'Erase All' or should you reformat every time to clear old images and refresh a previously-used card?"
My feeling from surfing about is that there's a lot of opinion ricocheting around and not much from substantial sources.
I might have failed in my efforts to get in touch with SanDisk, whose cards I've used for years, but I got an answer from Kingston Technology, a U.S.-based multinational. Wikipedia says that according to Gartner Inc., the information technology research and advisory company, Kingston is the #1 manufacturer of USB drives and the #3 maker of flash memory cards (although a quick scan of our usual suppliers, Amazon and B&H Photo, indicates that Kingston's lower-level cards are more readily available than its premier products).
I put the question like this: "Assuming a card (which has initially been properly formatted for the device) will be reused again and again in the same device (camera), what's the best way to erase the old images before reusing the card? [...] We're trying to establish 'best practices' that photographers should follow to optimize the reliability, dependability, and longevity of their flash memory cards."
This response came from Kingston Flash Engineer Tung Lam:
Most camera manufacturers follow the "Design rule for Camera File System" standard which specifies both directory and file structure for recording data to your device. Typically, when you format a card in your camera (or other device), it will follow this specification so that the file structure produced is exactly what the manufacturer expects. If you've seen a "DCIM" folder on your memory card before, this is the specification in action. Kingston always recommends that photographers format their memory cards within the device they intend to use the card in. This helps to ensure that the card is formatted correctly, will communicate with the device in the manner in which the manufacturer intended and helps prevent data corruption.
As a general rule, there are two options for formatting. A "format" is sufficient to clean the File Allocation Table (FAT) and refresh the card for subsequent use. A "low-level" format (not present on all devices) is designed to prevent users from recovering data in instances where one would want to dispose of the memory card. This approach could take a bit longer depending on the capacity of the card.
Followed by this from David Leong, Kingston's Public Relations Manager:
As a general best practice, Kingston recommends the user format the card.
When you select "erase," the data (e.g. an image) is still there. What is being deleted is the location of the photo stored in the File Allocation Table. "Erase All" deletes every single location in the File Allocation Table. Although the information in the FAT table has been erased, there can still be "residue" from the file. What can happen is the next time something is written in that spot, the controller on the card may decide to skip that spot or write a partial piece of data to it, while the rest of the data is stored elsewhere. This is called fragmentation. Similar to a hard-disk drive, fragmentation can cause performance issues. A "reformat" deletes the entire table and then creates a new one for the next use, meaning that as new information is written to the card, it is done sequentially in the FAT table.
So there's that. Looks like this one company's answer is that it's best to reformat every time. If I get answers from other companies I'll post them.
My thanks to Tung Lam and David Leong of Kingston Technology.
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Bob: "Oh good...I have been doing something correctly from day one (2000) of my digital camera experience to the present. That is not usually how it works for me."