Micro SD card or cards are found in a number of electronic devices where mounting space may be limited, typically cellular telephones, tablets, and some MP3 players. Their small size belies their storage capacity as some micro SD cards have as much as 64 gigabytes of storage.


SD stands for secure digital. The SD Card Association sets the standards for all cards of this type, ensuring that compatibility exists between differing manufacturers. Early in its development, some manufacturers set their own proprietary standards for SD cards, but these cards are comparatively rare.

Memory capacity of Micro SD Card

The cards have differing capacity. Standard capacity (SDSC) cards may contain up to 2 gigabytes. High capacity (SDHC) cards can store as much as 32 gigabytes, while extended capacity (SDXC) cards can handle up to a terabyte. The largest micro SC cards, however, are limited to 64 gigabytes.


The cards have three different physical sizes. Micro SD cards are the smallest at 15×11 mm. Mini SD cards are 21.5×20 mm, and standard SD cards are 32×24 mm. Their small size makes them susceptible to damage during insertion or extraction.

Care and handling

The connector has gold-plated contacts designed to withstand approximately 10,000 insertion cycles. Avoid touching the contacts, as skin oils can degrade the connection.

If cleaning is necessary, use a cotton swab moistened in alcohol. Let all the alcohol evaporate before installing the card. The outer plastic case is thin, so any side force applied to it can cause breakage. Micro SD cards can be particularly difficult to extract.

Use a fingernail or wooden tool like a toothpick or sharpened chopstick, not a metal tool that could puncture the case.


Adapters are available that permit using a micro SD card in a slot designed for a larger one.


Every SD card has a maximum data transfer rate. This is important in digital cameras because faster cards can store more photos or video before the internal buffer reaches its limit. In other words, a slow card might store five photos in rapid succession while a faster card can store 10 to 12. Video is affected in a similar manner.

The cards have two speed ratings: Speed Class and UHS Speed Class. The SD Card Association icon for Speed Class is a C surrounding a 2, 4, 6, 8, or 10, representing the data transfer rate in megabytes per second. UHS stands for ultra-high speed and transfers data as rapidly as 312 megabytes per second. devices intended for use with UHS cards will work with Speed Class cards, but not vice versa.

Performance will be limited to the normal data rate of the Speed Class card as a result. UHS micro SD cards are available for newer devices, but their storage capacity is limited to 16 gigabytes.


Most micro SD cards use a flash memory chip that incorporates wear leveling, a scheme to prevent the slow deterioration of individual memory locations through repeated read/write operations.

For the user, this means that filling the card to capacity before erasing it is one way to extend the card’s useful life. As memory locations fail, an internal program on the chip keeps track of them until the number exceeds a preset limit. When that happens, the card will no longer be useable.