A Secure Digital (SD) memory card is a portable flash memory chip used in devices like digital cameras, cellular phones, and audio players. The card is about the size of a postage stamp and comes in various capacities and transfer speeds. Generally speaking, the greater the capacity of the SD memory card, the faster the transfer speed.
Flash memory is the same type of memory used in memory sticks or flash drives. However, flash memory cards are formatted according to various specifications. Digital devices are designed to be compatible with one of the available card formats.
"SD" is a specific card format, based on the older Multi-Media Card (MMC) specification. The SD memory card is one of the most popular flash card formats in use today. The "Secure Digital" component of the card is a copyright protection scheme built into the chip. Content Protection for Recordable Media (CPRM) is intended to keep protected material from being excessively copied.
The SD memory card is a great way to store and transfer images, music, video and other data from a portable device to a PC. Some newer computers have a card reader built into the system, or an inexpensive external card reader can be purchased. Since there are many different types of flash memory cards, be sure the card reader is made for the specific type of memory card, or capable of reading various formats. Aside from the standard version, there are also miniSD and microSD cards. These cards are much smaller and not compatible with standard SD memory card slots.
The memory card might have a protective lock-switch at the top left. Sliding the switch into an open position allows the card to be written to or read. Sliding the switch closed allows reading only. This protects data from accidental overwrite.
SD memory cards come in various capacities, from 128MB to 1GB and more. Usually, a digital device is only designed to use cards up to a maximum capacity as stated by the manufacturer. A dated MP3 player, for example, might only be designed to use cards up to 512MB. In this case, a 1GB card will be unusable in the device, though any cards lower than the maximum capacity are fine.
When it comes to storing music or images, some people prefer to buy several smaller capacity SD memory cards in order to organize their library of data. It may be easier to locate songs or images you want by labeling several smaller cards. Others prefer getting the highest capacity card the device will support, to keep everything in one place. If this is preferred, it is wise to backup the card to the PC in case it the card is lost or damaged.
SD memory cards are available everywhere electronics are sold. As with other storage technologies, the prices tend to be dropping while capacity is increasing.