SD Card (Secure Digital Card) or memory card and its reader are non-volatile storage devices that do not require a power supply and maintain data in the NAND flash. SD Card is very small and has been popular for over 15 years. In 1999, it was relatively expensive and had a very low capacity. Later, entering the nanotechnology era, it became cheaper and had a higher capacity. Nowadays, the capacity of an SD Card ranges from 2GB, 4GB, 8GB, 16GB, 32GB, 64GB, 128GB, 256GB, 512GB, to 2TB recently. The price varies from hundreds to over ten thousand Baht following its capacity. Sometimes, even with the same capacity and brand, prices are different due to the grade of the material and, in more detail, the speed of reading and writing data. SD Card is classified by quality class, U, and connecting interface.
There are currently 3 types of memory card and its reader. The appearances are similar, but the interfaces, speed, and formatting are different. You should understand the differences and specifications before making any purchase, by making sure that your equipment works with SD, SDHC, or SDXC. This issue is mainly regarding the size of files, where those higher than 4GB per file should be used with exFAT SDXC, such as DSLR camera or VDO camera. Short clips should be used with SDHC that is FAT32 compatible where the price is more affordable, and there are more choices. The most popular type of SD Card nowadays is miniSD and microSD (TF) which come in a compact size in order to fit in with small devices, such as a smartphone, dash camera, and action camera. The size of microSD (TF) is close to pinky nail, and it may come in SD, SDHC, or SDXC format.
Look at the box or logo on the card, you will know what kind of card interface you should use. If there is no sticker, you can assume that it is UHS-I which could be used with SD, SDHC, and SDXC. Another type, UHS-II, has a larger contact space, transfer data faster, but can be used only with UHS-II devices. For the UHS-I, sometimes it is indicated as UHS, without I. It comes with 50MB/s and 104MB/s speed depending on whether it is SDHC or SDXC. For the UHS-II, the price is more expensive, but the speed is at 156 MB/s to 312MB/s. For general cards which are not UHS, the speed ranges from 12.5-25 MB/s are now rare.
The speed indicator of a memory card and its reader is another important factor to consider. It is called UHS Speed Class, abbreviated as U. For Full-HD VDO recording, using U1 is sufficient where the minimum Serial Data is at 10MB/s. For 2K and 4K VDO recording where it requires higher storage speed, using U3 is better. The current speed class is generally C10. The minimum speed of Serial Data is at 10MB/s. This can be used with both Full HD video recording and continuous shots. Some DSLR camera requires U3 card also due to the file size of up to 50MB when shooting at high speed. Currently, there are cards that support 30MB/s to 150MB/s. In conclusion, choosing a memory card and its reader is up to the suitability and requirements to meet the needs as much as possible.