How to choose an SD and microSD memory card

First generation SD cards (Secure Digital)

The first generation SD cards have two varieties, differing from each other in the maximum amount of data:

• SD 1.0 – from 8 MB to 2 GB;
• SD 1.1 – up to 4 GB.

The first SD storage devices saw the light at the very end of the second millennium - in 1999. They replaced MMC format memory cards, differing from them in the presence of their own microcontroller and a special protected area that excludes unauthorized access to data. Actually, this is where the name of the “Secure Digital” format came from. In addition, the safety of information is ensured by a special switch on the left side of the flash drive, which is responsible for write protection. When the slider is set to “lock” mode, recording and deleting data becomes impossible.

An important nuance. A flash drive does not provide one hundred percent protection against overwriting or deleting information using a mechanical slider - this function must be supported by devices in which the drive is used.

Out of the box, drives with a storage capacity of up to 2 GB are formatted according to the FAT16 standard, and up to 4 GB - FAT32.

SDHC (Secure Digital High Capacity) cards

The second generation of drives, announced in 2006, was named SDHC. Its main difference from the previous series was the increased capacity of the data storage: the minimum size of the SDHC format drive is 4 GB, and the maximum is 32 GB. The file system is represented by the FAT32 format.

SDXC cards (Secure Digital eXtended Capacity)

The most capacious and fast memory cards are represented by models with the SDXC index, first announced in 2009. The volume of such drives starts at 64 GB and can reach an impressive figure of 2 TB. In fact, flash drives with a capacity of more than 128 GB are not so common, which is facilitated by their high cost.

In 2013, a more advanced subspecies of SDXC memory cards was announced, which stands out for its increased data processing speed (up to 312 Mb / s) and the presence of an additional row of contacts: 17 for a standard form factor and 16 for microSD.

It is important to know! Drives are not backward compatible with previous generations. An exception to the rule is SDXC 3.01 format flash drives, which are compatible with some devices that can read data from SDHC cards. But the previous generations themselves are compatible with the next ones, i.e. modern gadgets that can read SDXC flash drives will easily accept SD and SDHC cards on board.

Consider the compatibility problem on a real example - based on a smartphone LG K10 8 GB / 1 GB of the 2016 model range. Its characteristics indicate the maximum possible volume of a memory card, which is limited to 32 GB. From this it follows that the phone is able to work with SD flash drives (capacity up to 4 GB) and SDHC (capacity up to 32 GB), but it cannot read SDXC cards.

Types of SD cards

SD drives are available in three different sizes:

• SD - 32x24x2.1 mm (often used in cameras and camcorders);
• miniSD - 21.5x20x1.4 mm (almost never found);
• microSD - 11x15x1 mm (the main type of drive for microSD, MP3 players, DVRs and other portable gadgets).

MicroSD memory cards can be adapted to larger slots using special adapters.

Speed characteristics and classes of memory cards

One of the most important characteristics of SD drives is the data transfer speed. It affects the stability of frames in video and the playback of large audio files, the possibility of continuous shooting with a camera or the quality of a video sequence recorded on a camcorder, etc. The value of the minimum guaranteed speed of writing files is encrypted in the class of the memory card, which is indicated directly on the flash drive itself in the form of a number framed by the letter "C".

Some manufacturers write the speed rating of a memory card the old fashioned way - as a number multiplied by the "x" index. The value of 150 kb / s acts as an x - this is the minimum speed for playing a CD, which was customary to be equal to at the dawn of the advent of SD cards.

In a separate line, it is necessary to highlight memory cards with support for the UHS (Ultra High Speed) high-speed data bus, which received a redefined assignment of some contacts to provide 4-bit information exchange.

The first generation of drives includes two varieties:

• UHS-I Class 1 - with a minimum data write speed of 10 Mb / s, and a maximum of up to 50 or 104 Mb / s (depending on the architecture);
• UHS-I Class 3 - with a guaranteed continuous write speed of 30 Mb / s, and a maximum of 50 or 104 Mb / s.

The second generation boasts the most outstanding speed performance of the entire SD card family. It is marked UHS-II Class 3, which guarantees a stable data recording speed at a speed of at least 30 Mb / s with a maximum overclocking of up to 156 or 312 Mb / s (depending on the architecture). On the body of the flash drive, support for a certain UHS class is indicated as the number 1 or 3, placed inside the letter "U".

Brief scenarios for using memory cards of various speed classes are shown in the table:

The potential of UHS-enabled drives is revealed only on devices with a compatible controller. Otherwise, the flash drive will work according to typical SD card algorithms with reduced data writing and reading speeds.

Important nuances

Before purchasing a memory card, be sure to ask what the maximum amount of memory your device can read. For example, the removable storage capacity of low-cost smartphones and car radios is often limited to 32 GB. At the same time, modern DSLRs and camcorders are able to take on board a flash drive with the maximum possible tank capacity (up to 2 TB).

The cost of SD cards directly depends on such parameters as the amount of data storage, the speed of information exchange and the name of the manufacturer. Some brands ( SanDisk, Kingston, Transcend) do not hesitate to provide a lifetime warranty on their creations, which is a weighty argument when choosing between an unknown brand and products of a famous company. In addition, top drives from well-known manufacturers often have additional protection against electromagnetic and X-ray radiation (found, for example, at airports), drops, moisture or vibrations. You should definitely pay attention to the last points when choosing a memory card for an action camera.

When operating the drive, try not to fill its tank to capacity. Full filling of the capacity of the memory card in some cases can lead to the loss of some information or malfunction of the flash drive. Data can almost always be recovered using special utilities or by contacting a specialized service centre, but the performance of all memory cells of the drive will most likely not be corrected.