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What Are SD Cards?

MP3 players utilize SD cards to store audio files.
Many phones use SD cards.
SDHC memory card.
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  • Written By: Victoria Blackburn
  • Edited By: Bronwyn Harris
  • Last Modified Date: 13 September 2014
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Secure Digital cards, or SD cards, are a non-volatile method of saving data for use in handheld computer devices. Non-volatile means that SD cards can save information even when the device is not receiving power. They are commonly used as a "bridge media" that can store data and be moved between different products. Developed by high tech companies such as Panasonic, SanDisk and Toshiba, they are commonly used as storage or memory cards for digital cameras, mp3 players, camcorders and notebook computers.

Standard cards measure 32 x 24 x 2.1mm, but mini (21.5 x 20.0 x 1.4mm) and micro (11.0 x 15.0 x 1mm) SD cards are also available. MiniSD and microSD cards were developed for the ever changing demand for smaller cell phones and handheld devices. Although smaller, the miniSD and microSD cards have the same storage ability as the standard sized SD cards. If required, the miniSD can be used in a standard SD slot with the use of a miniSD adapter.

To satisfy the industry’s hunger to have faster transfer rates, SD cards have been developed to provide more storage. The standard SD storage, which ranges from as low as 16MB and goes up to 2GB, has given way to the creation of a high capacity card that starts with 4GB storage and goes up to 32GB. This new card is called the Secure Digital High-Capacity (SDHC) card. In addition to the standard size, there has been the development of miniSDHC and the micro SDHC.

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Along with the storage capacity of SD cards, they are known for their speed of data transfer. The Speed Class Rating is the official unit of measurement for SD cards. There are four Speed Class Ratings: Class 2 guarantees a minimum transfer speed of 2 mega bytes per second (MB/s), Class 4 guarantees 4MB/s, Class 6 guarantees 6MB/s and Class 10 provides 10MB/s.

SD cards have become commonplace within the electronic device community and are a popular method of storing data on most digital cameras. They are shaped to avoid inserting the card the wrong way into the SD slot of the device. Also, the card’s electronic contacts are recessed beneath the surface of the card to protect them from being damaged by everyday handling. To determine the best card for the digital device that is being used first review the user manual to see which cards are recommended by the manufacturer.

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