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Micro-Secure Digital, or microSD, memory cards are interchangeable flash memory devicesthat support high-definition and full HD video recording through normal-speed bus interfacing. The micro designation refers to the physical dimensions of the card. All SD cards, including micro-sized versions, fit intotwo speed classes that indicate the type of video recording each card supports.
1. CLASSES
As of the date of publication, SD cards, in all their varieties, fit into two categories: Ultra-High Speed Class and Speed Class. The UHSC is comprised of just one subclass -- Class 1 -- that's designed to facilitate large-scale, HD, real-time broadcast-quality video through ultra-high speed bus interfaces. TheSC is made up of Classes 2, 4, 6 and10, which interface with high-speed or normal-speed bus interfaces. Class 10 SD cards are designed for full HD and HD still consecutive recording at high-speed bus interfacing. Classes 4 and 6 SD cardsare intended for HD video at normal-speed bus interfacing, while Class 2 cards are capable of standard-definition recording with normal-speed bus interfacing.
Class 2=2mb/s writing speed
Class 4=4mb/s writing speed
Class 6=6mb/s writing speed
Class 8=8mb/s writing speed
Class 10=10mb/s writing speed
The higher the class the better in speed in writing/reading.
►The image above is an example of a class 10 micro SDHC memory card.
2. TYPES
In addition to classes and physical dimensions, SD cards are distinguished by their type. Currently, SD cards are available in three categories: SD, high-capacity SD and extra-capacity SD. Each category contains SD, miniSD and microSD formats, except SDXC, which is comprised of SDXC and microSDXC versions. SD, miniSD andmicroSD cards offer up to 2GB of memory, while SDHC, miniSDHC andmicroSDHC cards provide between 2GB and 32GB. SDXC and microSDXCcards, the newest members of the SD family, offer between 32GB and 2TB of memory. Class 6 SD cards are produced in all SD card forms.
3. PHYSICAL DIMENSIONS
SD cards are available in several sizes, each distinguished by its standard, mini or micro physical dimensions. By virtue of the devicesthey are designed to interact with, SD cards are compact and lightweight in their design. SD, SDHCand SDXC cards are about the size of a postage stamp, measuring 0.9 inches wide, 1.3 inches long and 0.08 inches deep and weighing 0.07 ounces. MiniSD and miniSDHC cards measure 0.8 inches wide, 0.8 inches long and 0.06 inches deep and weigh 0.03 ounces and are about a third the size of SD, SDHC and SDXC cards. As the smallest of the SD card family, microSD, microSDHC and microSDXC cards areabout the size of a fingernail, measuring 0.4 inches wide, 0.6 inches long and 0.04 inches deep and weighing 0.02 ounces.
4. STANDARDS
Regardless of its category or speed class, each SD card is produced in accordance with the specifications and standards established by the SDAssociation. The SDA is an international collaborative organization composed of more than 1,000 electronics-related companies throughout the world that oversees the development of SD technology. Currently, SD cards are used in more than 7,000 products worldwide.
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