SD cards, or Secure Digital cards, are small removable flash memory cards commonly used in smartphones, tablets, digital cameras, and other devices to expand storage capacity. They are non-volatile memory cards that retain data even when not powered, and come in a range of sizes and speeds. Micro SD cards are a smaller version commonly used in mobile devices.
SD cards have largely replaced previous storage cards formats and are now a ubiquitous standard for portable storage. Their key advantages include small size, ease of use, good storage capacity, and affordability. SD cards allow people to store and transfer music, photos, videos, applications, and other files between devices.
How SD Cards Store Data
SD cards use flash memory technology to store data. Flash memory relies on floating gate transistors, which can retain data even when power is removed. Each floating gate transistor stores one bit of data based on the number of electrons trapped on the gate. Applying a charge adds or removes electrons, allowing the storage of binary data. The transistors are grouped into memory cells that each store multiple bits, with single-level cell (SLC) storing 1 bit per cell and multi-level cell (MLC) storing 2 or more bits per cell. Data is written, read, erased, and rewritten in blocks rather than individually accessing each cell. Flash memory cards are solid state with no moving parts, making them resistant to mechanical failure. They also consume less power and offer faster read/write speeds compared to hard drives (How Flash Memory Works, computer.howstuffworks.com).
Physical Damage
One common cause of SD card failure is physical damage from dropping, bending, or otherwise mishandling the card. SD cards contain delicate internal components that can break if exposed to physical shock or stress (Source). For example, dropping an SD card on a hard surface can cause the tiny solder connections to crack or detach from the circuit board. Bending or snapping a card can fracture the embedded NAND flash memory chips or damage the copper traces connecting them. Even small amounts of physical damage can render the card completely unusable and make data recovery difficult or impossible (Source).
SD cards are not designed to withstand physical abuse or force. Their small size and portable nature also make them prone to being damaged in accidents. While a physically damaged SD card often cannot be repaired, a data recovery service may be able to extract the data if the memory chips themselves remain intact. However, extensive physical damage usually makes data recovery infeasible (Source). The best protection is to handle SD cards carefully and avoid dropping, bending, snapping, or applying pressure to them.
File System Corruption
One of the most common causes of SD card corruption is improper shutdowns while the card is being written to. SD cards use a file allocation table (FAT) to organize data on the card and track what clusters or sections of the card are occupied by files. If the card loses power or is removed before a write operation completes, this file allocation system can become corrupted with invalid data. The card may appear blank or show some files missing when next accessed because the locations of file data is no longer accurately tracked by the FAT.
According to the EmbeddedTS article Filesystem Corruption with SD cards, “The most common issue resulting in data corruption is when powering off SD cards in the middle of a write.” The FAT can be left in an intermediate state if a write is interrupted. This filesystem corruption prevents the data on the card from being properly read and accessed.
Wear and Tear
SD cards have a limited lifespan due to wear and tear from repeated rewrites. Flash memory cells can only withstand a finite number of erase/write cycles before they begin to degrade and eventually fail. According to What is the Lifespan of an SD card and How to Check It, the number of rewrite cycles for SD cards can range from 1,000 to 100,000 writes per cell. Higher quality and newer SD cards generally have a higher rewrite tolerance.
During normal usage, small portions of the memory get rewritten frequently, while other areas are rarely modified. This uneven wear causes certain cells to fail sooner than others. While the SD card may still be functional after exceeding the maximum rewrite cycles, data retention and read/write performance will steadily decline as more cells wear out. To prolong the lifespan, it’s best to avoid excessive writes and rewrites whenever possible.
Repeated removal and reinsertion of the card can also contribute to wearing of the physical pins and contacts. However, the electrical degradation has a greater impact on lifespan compared to mechanical wear for SD cards.
Manufacturing Defects
Although rare, some SD cards can fail right out of the box due to manufacturing defects. This typically occurs due to issues in the production process, such as:
- Contaminants getting embedded in the memory chips during fabrication.
- Improper bonding of components on the circuit board.
- Faulty or low-quality memory chips being used.
- Problems with the controller firmware.
Most major brands thoroughly test cards after production to catch defects. But some still occasionally slip through quality control. Defective cards often fail quickly with errors during initial use or formatting. Thankfully manufacturers typically honor warranties for DOA cards. Checking online reviews can help avoid brands with higher defect rates.
Overall, manufacturing issues are quite uncommon compared to other SD card failure modes. But it remains a possibility, especially with cheaper no-name cards. Carefully buying from reputable brands helps minimize the chance of getting a defective card.
Data Retention
SD cards can retain data for many years without power. This is because they use flash memory rather than traditional magnetic hard drives. The data is stored in transistors which do not require continuous power to maintain state. According to one source, SD cards can retain data for up to 10 years in ideal conditions with no physical damage (source).
However, the data retention ability does slowly degrade over very long time periods. After 10-20 years, a small percentage of the data may become corrupted or lost as the flash memory transistors slowly leak their charge state. But an SD card that is stored properly should be able to hold the vast majority of data intact for at least a decade without power.
For archival data storage spanning multiple decades, it’s recommended to occasionally power up the SD card and rewrite the data to refresh the card. This will ensure the data remains intact over very long periods. But for medium term storage of up to 10 years, SD cards can reliably store data without any external power source.
Detection and Recovery
There are a few tools and techniques you can use to detect and repair bad sectors on an SD card:
First, you can use the built-in error-checking tool in Windows called CHKDSK (source). To use CHKDSK, insert your SD card into your computer, open the command prompt as administrator, and type “chkdsk x: /f” where x is the drive letter of your SD card. This will scan the drive and attempt to repair any file system errors.
You can also use third-party SD card recovery software like Disk Drill (source), Recuva (source), or EaseUS Data Recovery Wizard (source). These tools can scan the SD card, identify bad sectors, and recover data from damaged areas of the card.
Finally, you can use advanced disk utility tools like TestDisk (source) or PhotoRec (source) to scan the drive, repair file system issues, and restore lost files. These are more complex to use but can help recover data even from significantly corrupted cards.
Prevention
There are several best practices you can follow to maximize the lifespan of your SD cards and prevent issues:
Always safely eject the SD card before removing it from your computer or camera. Suddenly cutting power can corrupt data (source).
Avoid exposing your SD cards to extreme heat, cold, or moisture. Store them in a dry, room temperature environment (source).
Be gentle when handling the cards to prevent physical damage. Do not bend, drop, or scratch them.
Keep the cards in a protective case when not in use. Avoid touching the contacts.
Format your SD cards in the camera rather than your computer for optimal performance.
Replace old or damaged cards. The cost of a new card is minimal compared to lost images and videos.
When to Replace
There are a few key signs indicating it may be time to retire an old SD card and replace it with a new one:
Performance issues like slow transfer speeds, long loading times, and freezing could all be indicators of a failing SD card. As cards wear out, their ability to reliably read and write data decreases. If you notice your device taking much longer than usual to load apps, photos, or videos from the SD card, it likely means the card is nearing the end of its usable lifespan.
Another sign is more frequent error messages, especially related to corruption like “SD card errors” or “SD card not formatted.” As cards deteriorate, the integrity of data on the card becomes compromised. You may encounter more random errors when trying to access files. Data corruption is a big red flag that the card is no longer dependable for storage.
Additionally, if your SD card is more than a few years old, replacing it as a precaution is recommended. Age alone can cause gradual performance decline. Standard SD cards typically last around 5 years with average use before needing replacement. High-end cards may last up to 10 years. But all cards have a finite lifespan, so periodic replacement can avoid failures.
Lastly, if your SD card has sustained any significant physical damage like cracks, dents or water damage, it should be immediately replaced. Physical defects vastly accelerate deterioration and increase the risk of total card failure.[1]