SD (Secure Digital) memory is a small card, most commonly the size of a postage stamp, that is used in a wide variety of multimedia devices. SD cards are a form of solid-state memory device known as Flash memory. Because it is solid-state memory, as opposed to the magnetic memory used in normal hard drives, it is much more durable and is not damaged when it comes in close proximity to a magnet. SD cards were developed to be competition for MMCs (MultiMediaCards).
History
SD cards first made their appearance in 2000, released by Panasonic, Matsushita, and Toshiba. The design of SD cards allows them to be much smaller than the Intel-based memory modules such as CompactFlash cards. SD cards were developed with the advantage of a write-protection switch that prevents loss of information stored on the card.
Function
Every SD card has a tiny chip known as a microcontroller on it. This microcontroller handles all communications between the media device and the card, getting information from the card and putting information onto the card. The microcontroller only operates when data is being sent to or read from the card. All microcontrollers operate from an internal clock signal, and an SD card's clock is controlled by the media device it is plugged into. When the clock isn't in operation, neither is the microcontroller. The media device only runs the onboard clock on the card when it wants to transfer data to or from the card.
Variants
SD cards come in three variants. The first variant is known simply as Standard SD. Standard SD cards have a capacity of 4 megabytes all the way up to 4 gigabytes. The next variant is SDHC, or SD High-Capacity. SDHC cards have a capacity ranging from 4 gigabytes to 32 gigabytes. The newest variant is SDXC, or SD extended capacity. SDXC cards have a capacity of 32 gigabytes but are defined to have a maximum capacity of 2 terabytes. SD cards also have a variety of sizes, including the smaller Mini SD and even smaller Micro SD cards. Either one of these can fit in an SD slot with the use of an adapter.
Devices
SD cards are able to work in a wide range of devices. These devices include digital cameras, digital camcorders, mobile phones, MP3 players and PDAs (personal digital assistants). As technology has improved, these cards have allowed higher and higher storage capacities for devices. SD cards can also be inserted into most modern computers that possess MultiMediaCard slots.
Care
Although SD cards are relatively durable, there are several precautions to take to avoid damaging them. Most cards come with a plastic case. Store the card in this case when it is not in use. Never store the card in direct sunlight, as the heat can cause the plastic casing to warp, and excessive heat can also damage the electronic components inside the card. Avoid submerging the card in any liquids as this can cause short circuits the next time the card is connected, resulting in irreversible damage to the card and potential damage to the media device.
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