What is an SD Card?
An SD card, or secure digital card, is a small removable flash memory card used for storing digital data. “SD” stands for secure digital. SD cards were first introduced in 1999 by Panasonic, SanDisk, and Toshiba as an improvement over MultiMediaCards (MMC) (Lenovo). They have become a ubiquitous storage medium for digital cameras, mobile phones, handheld computers, and many other portable devices.
There are several types of SD cards that have evolved over the years, including SDHC (high capacity), SDXC (extended capacity), miniSD, and microSD cards. The microSD card is the smallest, about the size of a fingernail. SD cards use flash memory to store data non-volatilely, meaning the data remains even when power is removed from the card (Wikipedia).
Common uses for SD cards include portable storage for photos, videos, music, documents, apps, and other files. They allow you to easily transfer data between devices like cameras, phones, laptops, gaming systems, and more. SD cards are inexpensive, rewritable, small, and durable.
Storage on SD Cards
SD cards store data by using flash memory, which is a type of non-volatile memory that can be electrically erased and reprogrammed. Data is stored in memory cells made up of floating-gate transistors. Electrical charges are used to change the state of transistors between 1 and 0 to represent binary data. This allows data to be stored even when power is turned off.
SD cards typically use the FAT32 file system to organize data. This divides the memory into clusters or allocation units. When a file is saved to the card, it occupies one or more allocation units. The file system keeps track of which units are associated with each file. This allows data to be stored and retrieved in an organized fashion.
As more data is written to the card, more allocation units get used up. The file system handles where data is physically located on the memory, so files can be stored in a fragmented way across different regions of the card. But the logical mapping makes this transparent to users.
Overall, the combination of flash memory cells and the file system allows SD cards to reliably store large amounts of data, photos, videos, and other files.
Removing vs Ejecting an SD Card
There is an important difference between simply removing an SD card and properly ejecting it first. Removing an SD card without ejecting can lead to data corruption or loss. This is because when a card is in use, data may still be buffered and not actually written to the card yet. Ejecting the card ensures any buffered data is flushed and the card is no longer in use before removing it.
On Windows, you should always use the “Safely Remove Hardware” option to eject an SD card before taking it out. On Android, you can unmount or eject the SD card from the Storage settings. Simply popping the card out without ejecting has risks. The proper eject process stops all I/O operations and unmounts the drive so it can be safely removed.
Some key differences between removing vs ejecting an SD card:
- Ejecting flushes any cached data and ensures writes are complete before removing.
- Simply removing risks data loss or corruption if data is still buffered.
- Ejecting properly unmounts the drive so the OS knows it’s safe to remove.
- Removing without ejecting could confuse the OS leading to errors.
In summary, always properly eject an SD card first before removing it from a device or card reader to prevent any data issues.
Does Removing Delete Data?
Simply removing an SD card does not delete the data stored on it. When you remove an SD card, you are physically disconnecting it from the device, but the files remain intact on the card itself. The data exists independently on the SD card and is not reliant on the connection to the device to persist. As long as the removal is done safely before unmounting, the data remains undisturbed on the SD card even after disconnecting it.
According some experts, “Generally speaking, it won’t delete data from your SD card, unless the transferring is not finished before you removing it” (Source). So in most cases, simply sliding the SD card out of its slot does not actually modify, delete or format the data on it in any way. The data remains fully intact and accessible once the card is re-inserted or accessed from another device.
In summary, the physical disconnection involved in removing an SD card does not affect the integrity of the data stored on it. The files remain in their original state even after the card is taken out of the device safely. So no, simply removing a card does not delete everything or cause data loss.
When Does Data Get Deleted?
When you delete a file from an SD card, it isn’t instantly and permanently erased. The SD card uses a file system, such as FAT32 or exFAT, to organize data and track which storage sectors are occupied or free. When deleting a file, the file system removes the directory entry and marks the space as available rather than erasing the actual data right away. This is known as reference counting.
The file data remains intact in the same physical location until the storage sectors are overwritten by new data. The file system will eventually reuse the marked sectors through a process called garbage collection. But there is a window where deleted files can be recovered before being overwritten.
On SD cards and solid state drives, garbage collection is less frequent compared to traditional hard drives. This means deleted files may persist for weeks or longer if the space hasn’t been reallocated and overwritten (source). So removing an SD card right after deletion does not immediately destroy files.
Recovering Deleted Files
When a file is deleted from an SD card, the reference to that file’s data is removed from the file system, but the actual data usually remains on the card until it is overwritten by new data. This means deleted files can often be recovered using data recovery software as long as the SD card hasn’t been overwritten.
There are many free and paid SD card data recovery programs available that can scan a card and recover deleted files like photos, videos, documents, and more. Some popular free options include Disk Drill, Recuva, and PhotoRec. These allow you to quickly scan an SD card and restore deleted files by clicking on them and recovering them to another location.
Recovery software works best if you stop using the SD card right away after deleting files, as overwriting data makes it much harder to recover. The longer you wait, the more likely critical data will be overwritten. So act quickly after any accidental deletion. With the right software, you have a good chance of getting lost files back.
Securely Erasing an SD Card
Simply formatting an SD card does not permanently erase the data on it. Formatting only removes the index of where files are located, but does not overwrite the actual data. This means the files can be recovered using data recovery software.
To securely erase an SD card, you need to completely overwrite the data. This is done by using a secure erase technique that writes random data over the entire card multiple times. This overwriting renders the original data unrecoverable.
On Windows, you can use the free EaseUS Disk Wiper tool. It offers an SD card eraser mode that can perform a secure erase by overwriting data up to 35 times. You can also use the built-in Diskpart tool in Command Prompt to clean the SD card.
On Mac, the Disk Utility app provides a secure erase option when reformatting an SD card. It overwrites data with zeroes to prevent recovery.
On Android, you can encrypt the SD card before reformatting it. This scrambles the existing data, making it impossible to recover. Some Android tools like SanDisk Memory Zone also let you permanently erase SD cards.
Performing a full secure erase on the SD card ensures no data can ever be recovered from it. This is important before selling, donating or disposing of an SD card.
Other Causes of Data Loss
In addition to removing or ejecting the SD card improperly, there are some other common causes of data loss or corruption on SD cards:
Corruption: File corruption can occur due to faulty hardware, problems during file transfer, malware infection, or errors in the filesystem itself. This can prevent access to files or make them unreadable.1
Physical damage: Dropping, bending, or otherwise physically damaging an SD card can destroy or disable components required to read data. This is especially risky for small microSD cards.2
Malware: Viruses, spyware, and other malicious software can attack files on an SD card and encrypt or delete them. Always scan cards from untrusted sources.3
Accidental overwrite: Saving new files to an SD card without backing up old ones can inadvertently overwrite and delete the original data.
Backing Up an SD Card
It’s crucial to regularly back up the data on your SD card to avoid permanent data loss. Backups provide you with a copy of your files in case your SD card becomes corrupted, damaged, or erased.
There are several options for backing up an SD card:
- Use backup software like EaseUS Todo Backup which allows you to directly backup SD card data to your computer or external hard drive (https://www.easeus.com/backup-utility/how-to-backup-sd-card-before-formatting.html).
- Manually copy and paste files from the SD card onto a computer, external drive, or cloud storage.
- Upload important photos, videos, and documents to cloud storage services like Google Drive or Dropbox for offsite backup (https://www.cbackup.com/articles/how-to-backup-data-before-formatting-sd-card.html).
Regularly backing up the SD card to multiple locations ensures you have multiple copies of your data safe in case of accidental deletion, corruption, or physical damage to the card.
Summary
To recap, simply removing an SD card does not delete the data stored on it. The data remains intact on the card unless it is intentionally erased or the card is reformatted. Proper ejection protocols should be followed before removing the card to prevent corruption. However, even corrupt data is often recoverable with the right software tools.
While the data itself is not deleted when the card is pulled out, some operating systems may not recognize the files if the card is reinserted before proper ejection. The files themselves still exist in full on the card though.
If you wish to securely erase an SD card, use disk utility tools to overwrite the data before reformatting. Otherwise, simply reformatting only removes the file pointers to the data, not the data itself.
To prevent accidental data loss, be sure to regularly back up the contents of your SD cards. Follow proper protocols for ejection before removing the card, use file recovery software if needed, and overwrite or reformat the card when intending to permanently delete all its contents.