Android SD Card Format and Specification

Capacity level and the corresponding file format of mobile phone SD card

In order to meet people’s personalized needs for mobile phone memory, some mobile phones have set external memory, which is commonly known as the mobile phone memory card. Nowadays, the common mobile phone memory cards on the market are MMC, SD, miniSD, Memory Stick and SM. At present, there are three levels of SD card capacity, respectively SD, SDHC and SDXC.

The following is the capacity level and the corresponding file format of mobile phone SD card:

Introduction of Android SD card formats

FAT is a file system invented by Microsoft and partially patented. It has not been complicating, and supported by almost all operating systems.

FAT 12

The original FAT, now commonly known as FAT 12, does not support hierarchical structure, which cluster addressing only has 12 bits, and only supports partitions up to 32 MB. Because the only root directory of FAT 12 must also be placed in the first track, the number of files it can store is limited to several dozen.

FAT 16

Firstly, the maximum disk partition of FAT 16 is only 2 GB, which is no longer suitable for the current large capacity SD card. Secondly, due to the limitation, the cluster size used in FAT 16 must be enlarged to accommodate larger disk space after each partition exceeds a certain capacity.

For example, if you need to store a 1 KB file in a 1000 MB disk partition, it takes up 16 KB instead of 1 KB, which is a waste of 15 KB. Therefore, the storage mode of FAT 16 will lose a certain amount of disk space invisibly.

The following is the relationship between partitions and cluster size of FAT 16:

FAT 32

After using the partition table form of FAT 32, we can define SD card as one partition instead of multiple partitions, which facilitates the management of SD card. For example, now there are two partitions of 2 GB in size, one using FAT 16 file system and the other using FAT 32 file system. The cluster size of the former is 32 KB, while that of the latter is only 4 KB, which greatly improves the utilization of SD card.

But FAT 32 also has the disadvantage that when a file is deleted and rewritten, it doesn’t write it back in full fragments. Over time, the files in the SD card will gradually become scattered, thus slowing down the speed of reading and writing.

exFAT

In order to solve the problem that FAT 32 does not support 4 GB and larger files, exFAT came into being. It is a file system especially suitable for flash memory, but not for disk.

How to recover data after formatting the mobile phone SD card?

Renee Undeleter is comprehensive SD card file rescue software. It not only supports saving various types of fileswhich is deleted by mistake, but also has a good effect on saving formatted disk, especially SD card formatted rescue for Android phone or other devices.

It is worth to try Renee Undeleter which has three scanning schemes including built-in file recovery, format recovery and partition recovery, which can meet the different needs of users. At the same time, the interface of it is simple and clear, even novice can easily complete the operations.

1. Connect SD card to computer through card reader, open Renee Undeleter, and select “Fast Partition Scan”.

2. Select the partition where the SD card is located, and then click “Next”.

3. The scanning time is determined by the size of SD card. The memory of SD card is larger, the scanning time is longer. After the scanning finishes, select the file you want to recover and click the “Recover” button.

How to encrypt the mobile phone SD card

After opening “Settings”, select “Advanced Settings” and enter the “Security” interface. Click “Encrypt external SD card“, enter characters according to the prompt to set the password for the card.

Knowledge expansion

In addition to the above mentioned knowledge, we also listed the processing methods of the mobile phone SD card cannot read the file, as well as its SDHC standard and Class transmission speed level.

How to solve mobile phone SD card cannot read data

The following reasons may cause the SD card unable to read the files normally.

1. The contact points of SD card are not clean.

By observing whether there are spots in the metal area of SD card, we can infer whether the contact points of SD card are clean. If it is found to be covered with dust or grease, you can use cotton cloth with alcohol or water to wipe it, and then reinsert the SD card after the water is dried.

2. The battery voltage of mobile phones or portable devices is unstable.

Because high quality SD cards are very strict in the power supply of mobile phones or portable devices when reading files, it is possible that SD cards cannot read files properly if the batteries of the devices are not original. In this case, it is recommended to install the original battery and try again.

3. The slot of the mobile phone or portable device is squeezed

If the thick irregular batteries are used, the card slots of mobile phones or portable devices will be squeezed, which results in card reading is not smooth. Please replace the original battery and find something to hold up the slot. In this case, you can try to pick the wire down a little with a needle.

4. The wire inside the slot is rusted or excessively bent

Put the slot facing the sunlight and observe whether the wire contacts inside are at the same height. If not, it may be due to the frequent insertion of SD cards, resulting in excessive bending or rusting of the wire in the slot. In this case, you can try to pick the wire down a little with a needle.

5. SD card is infected with virus

Scan the SD card with anti-virus software. If you find the virus, format it on the computer (select FAT format).

6. Incorrectly format the SD card

Formatting on mobile phone is different from that on computer. If SD card suffers from incorrect formatting, please follow the instructions and format it again with the computer (select FAT format).

SDHC standard of SD card

All SD cards with capacity greater than 2GB must conform to SDHC specifications. It is pointed out in the specification that such SD cards should at least meet the speed grade of Class 2, and SDHC and speed grades must be printed on the cards. If one of them is missing, it is likely that this type of SD card will have compatibility problems with the device when used.

In addition, SDHC standard of SD card must adopt FAT 32 file system. This is because the maximum capacity supported by FAT 16 file system is 2GB, which does not meet the requirements of SDHC.

Transmission speed level

Different SD cards read and write files at different speeds. The higher the Class level, the faster the file transfer rate.

Class 0：Includes cases below Class 2 and unlabeled Speed Class.

Class 2：The minimum transmission speed is 2MB/ s, and you can watch ordinary movies.

Class 4：The minimum transmission speed is 4MB/ s, and high-definition movies can be played smoothly.

Class 6：The minimum transmission speed is 6MB/ s, which can meet the continuous shooting of SLR cameras and the requirements for the use of professional equipment.

Class 10：The minimum transmission speed is 10MB/ s, which can meet the storage requirements of higher rate.