SD Card Test and SD Card Test Pro documentation
Internal SD card: this is the built-in (not user removable) SD card in your mobile. Basically it can be an eMMC or UFS card (see later).
Removable SD card: this is the external SD card, with this card you can extend your mobile if it supports. Basically it can be Micro SD, SDHC and SDXC card (see later).
Flash memory type: It can be eMMC or UFS (see later). SD Card Test app will detect the type of the SD card based on the result of the speed test. To select the best category, during the test the application has to process at least 4 GB of data and the test has to run at least for 10 seconds.
eMMC: Flash memory type. It’s the old multimedia card standard. This is definitely slower than the new UFS standard, the maximum write speed can be around 100 MB/s or lower.
UFS: Flash memory type. Universal Flash Storage, this is the new standard for internal SD cards. The maximum write speed can be 600 MB/s or higher
File system: In computing, a file system or filesystem is used to control how data is stored and retrieved. There are many different kinds of file systems. Each one has different structure and logic, properties of speed, flexibility, security, size and more (from Wikipedia)
EXT4: it’s a modern journaling file system developed for Linux-based systems (and Android system is based on Linux). Max file size can be even 16 TB.
exFAT: it’s a modern file system, optimized for flash memory such as USB flash drives and SD cards. The maximum file size can be even 128 PB.
FAT32/VFAT: it is commonly used on small devices, like floppies, or temporary drives, like a flash memory drive. It’s an old file system with a lot of limitations. The maximum file size can be only 4 GB. It’s better to use exFAT for bigger SD cards.
Speed Class: this is classification method based on the speed of the SD card, to help to the customers to decide which card fits to their demand to the best.
For example Class-10 or UHS-I or V10 means the minimum sequential write speed is 10 MB/s. UHS-3 or V30 means 30 MB/s.
SD Card Test Android application will detect the class of the SD card based on the result of the speed test. To select the best category, during the test the application has to process at least 4 GB of data and the test has to run at least for 10 seconds.
Data verification technology (Verify written data): This is a professional feature in SD Card Test Pro app. When you enable this feature, the application will generate and write random data to the disk. During the write, it calculates the hash of the random data and stores it. When you run a read test, the app will read the random data from the disk and it calculates the hash of the read data.
When read test is finished, SD Card Test Pro will compare the hashes of the written and the read data. If they are the same, the card is not damaged and what’s more important, it could store as many data on the disk safely as you set in the settings in file size. If the hashes are different, then either the SD card is damaged or fake. Why is this important? See below.
Fore more information about this technology, see this blog post: How data verification technology works
How to set it: https://www.youtube.com/watch?v=ZO_Hj8WWIc4
Card is damaged: in that case you can write data to the SD card, but the system won’t be able to read all of the data again that means these data is lost. I don’t think I should highlight the level of the headache when you are loosing something important and you recognize it only when you need it… If SD Card Test Pro detects this error, you should not store any important data on this card anymore.
Fake SD card – wrong disk space: The most fake SD card simulates a big space but can store only a small amount of data. For example you have bought a 64 GB of (fake) SD card that can only store 8 GB of data. When you put it into your mobile, the system will recognize it as a 64 GB of storage, because the fake SD card lies to the operating system. The most funny thing is in fact, that you can write 64 GB of data to this card. But this is a one-way ticket, you are not able to read those data anymore they are lost and you will only recognize it when you need these data. Sometimes it’s too late.
If you set 64 GB as file size in SD Card Test Pro (to fill this example SD card), enable “Verify written data”, then run a write and read tests, it will detect that your card is fake, because the hashes will be different.
Hash: The hash is a number generated from a string of text. It is substantially smaller than the text itself, and is generated by a formula in such a way that it is extremely unlikely that some other text will produce the same hash value.
Fake SD card – wrong speed: Sometimes a fake sd card is just lying about the speed. It is labeled as UFS-3 (means at least 30 MB/s of sequential write speed), but it is just only an UFS-I card (10 MB/s) or worse. In that case just run a write test, and the app will detect the class of the type.
Sources:
https://en.wikipedia.org/wiki/ExFAT
https://en.wikipedia.org/wiki/ExFAT
https://en.wikipedia.org/wiki/MultiMediaCard
https://en.wikipedia.org/wiki/Universal_Flash_Storage
https://www.sdcard.org/developers/overview/speed_class/