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Why format a flash memory card?

Memory card formatting is the process of preparing a flash device for data storage. It cleans the SD or Compact Flash card by removing previously existing data and information on the card ("low level formatting") and creating a new file system ("high level formatting").

Sandisk memory
Popular memory cards

Most memory cards are nowadays pre-formatted when reaching the consumer and do not need to be further initialized before their first use, although running the formatting procedure does not have any adverse effects. Subsequently it is good practice to format memory cards occasionally (that is, perhaps once per month) in order to maintain the card's full speed performance, preserve its storage capacity and reduce the risk of storage errors. Moreover, there are cases, such as when the file system on a memory card got corrupted or when a card was infected by a computer virus, that call for a throrough card cleanup through formatting.

Memory card formatting can be undertaken through the camera or through a computer. In the latter case, a memory card reader that connects to the computer is required. Both methods clean out all files and set up the memory card for use in the camera. Formatting a card with a computer is often faster, while in-camera formatting is generally recommended for obtaining a file system that is optimized for the particular camera it will be used with.

How does formatting differ from erasing images?

Digital cameras and computers offer two ways to remove information from memory cards: formatting wipes the entire card clean, while erasing/deleting destroys the file system that tells the device where the data is located for individual images. When using the erase/delete function, the actual image data remains on the memory card, but will be overwritten when new images are taken. Erasing/deleting individual or groups of images is quick, while formatting a card can take several minutes.

As image data remains on the card following an erase/delete operation, it is often possible to recover parts or all of the images that might have been removed accidentally. Specialized software packages are available to perform this task. In contrast, a formatted memory card loses most of its imaging information irreversibly, so that care should be taken for all valuable image data to be transferred to other storage media before the formatting operation is launched. That said, there is software to help recover data from formatted memory cards, but the recovery success rate is significantly lower than in the case of recovery attempts following erase/delete operations.

When is it desirable to format a card?

Formatting a memory card is a little bit like spring cleaning. It is good to clean up and put one's house in order once in a while, but it takes time to do so, so that you do not want to perform the operation every day. Simple erase/delete operations leave fragments of previous imaging data on the memory card. These remnants can pile up and make the card more susceptible to errors or failures. To come back to the housekeeping analogy, the fragments of old image data are like old car parts and accessories that pile up in the garage and need to be cleaned out from time to time in order not to get into the way of the car. There is no general rule how frequently a memory card should be formatted, but doing so about once a month should keep your flash memory device at its peak capacity for long. if you shoot, transfer, and erase lots of photo, you might want to format the card more frequently.

There are also emergency cases of memory cards not functioning properly or triggering error messages. Possible reasons for these failures might be a corrupted file system on the device or infection with a computer virus. Formatting the card can then often restore its full functionality.

Last but not least, it might be desirable to wipe a memory card clean before passing it on to others or selling it (possibly in connection with the camera), so that strangers can not recover and browse through one's photos. Formatting will remove all imaging information. If you want to be sure to have an absolutely clean card, you might even want to undertake a three step procedure: (1) format the card; (2) fill the card with images of a neutral subject (your favorite brick wall); and (3) format the card again.

How to format a card inside a camera?

Formatting a memory card inside the camera in which it will be used is a very good means of maintaining a card's full capabilities. While the exact formatting procedure and menu display may differ between cameras, the following ten-step guidelines will be able to perform the task for most cameras.

Card formatting
Formatting menu
  1. Turn the camera off and insert the memory card you wish to format into the camera's memory card slot.
  2. Turn the camera on and verify that the battery is well charged. If necessary, recharge the battery.
  3. Verify that all valuable information on the card has been backed-up. If not, transfer the imaging data you want to keep to another storage medium.
  4. Press the Menu button to activate the Menu display on the rear screen.
  5. Navigate to the "Format" or "Format Memory Card" item in the menu, which is often found within the "Setup" screen.
  6. Select/highlight the "Format" or "Format Memory Card" item and then press "OK".
  7. In case a confirmation message appears, confirm your intend of formatting the card by selecting "Yes" and pressing "OK".
  8. Wait until the formatting process, which for large memory cards can take several minutes, is completed. The end of the formatting procedure will normally be indicated on the rear screen.
  9. Turn off the camera once the process is completed.
  10. Congratulations, you now have a clean and well formatted memory card!

In case this process does not apply to your camera, please consult the camera's instruction manual or contact the manufacturer's technical support staff for further guidance.

How to format a memory card with a computer and card reader?

If you have a memory card reader available, you can also format your flash memory device with your computer. This process is normally quicker than using a camera for formatting. Also, using a computer has the advantage of being able to use specialized software. For example, the SD Association makes a package available as a free download that provides for a tailor-made formatting process for SD/SDHC/SDXC cards.

The standard formatting procedures differ slightly by computer operating system. Here is the list of ten steps to undertake for a Windows-based PC (see below for corresponding Mac instructions):

  1. Insert the memory card you wish to format into the memory card reader, and then connect the memory card reader to the computer.
  2. Click on "My Computer", and navigate to the removable drive that represents the slot of the memory card reader that contains the memory card.
  3. Verify that all valuable information on the card has been backed-up. If not, transfer the imaging data you want to keep to another storage medium.
  4. Right-click on the removable drive letter connected to your memory card and select "Format". Make sure you select the correct drive letter in order to avoid erroneously removing information from another drive.
  5. Select a file format system: choose "FAT" for cards up to 2 GB; choose "FAT32" for cards up to 32 GB; and choose "exFAT" for cards larger than 32 GB.
  6. Leave the "Quick Format" checkbox unchecked for a thorough formatting, or check it if you prefer a quicker, but more superficial process.
  7. Press start to launch the formatting process.
  8. Confirm that you want to format the selected drive.
  9. Once the process is completed, eject the memory card by clicking on the respective icon at the bottom right of the screen, and remove it from the card reader.
  10. Congratulations, you now have a clean and well formatted memory card!

Similarly, if you are using a Macintosh computer, you would proceed through the following ten steps:

  1. Insert the memory card you wish to format into the memory card reader, and then connect the memory card reader to the computer.
  2. Verify that all valuable information on the card has been backed-up. If not, transfer the imaging data you want to keep to another storage medium.
  3. Doubleclick on "Macintosh HD".
  4. Click on the "Applications" folder.
  5. Click on the "Utilities" folder, and then double-click on "Disk Utility".
  6. Select the drive capacity corresponding to the memory card you intend to format.
  7. Click on the "Erase" tab and verify that the Volume Format is labelled "MS-DOS file system".
  8. Select "FAT" from the menu options, and then press "Erase".
  9. Once the process is completed, eject the memory card, and remove it from the card reader.
  10. Congratulations, you now have a clean and well formatted memory card!

Further Reading

Modern digital cameras are becoming more and more sophisticated and require higher performance memory cards. One critical criterium when purchasing a new card is therefore its speed class, so as to make sure that the storage device does not become the bottleneck of the imaging pipeline. Technological change rather than technical failure is also the main reason for memory cards to be ditched. In fact, some card formats, such as compact flash type II cards or xD-picture cards, have over time become obsolete and are no longer supported and used in modern cameras.