Expandable Memory lets mobile devices use additional removable memory
cards for increased storage space. Memory cards are non-volatile, meaning
they do not need power to maintain the information stored. In addition,
memory cards offers fast read access times and better kinetic shock resistance
over hard disks, ideal for storage on portable devices due to being able
to withstand intense pressure, extremes of temperature and immersion in
water. Different card formats exist in the mobile arena, varying in size
and storage capacity:
MMC (MultiMediaCard) - Unveiled in 1997 by Siemens AG and SanDisk,
MMC is about the size of a postage stamp: 24 x 32 x 1.4 mm. Originally using
a 1-bit serial interface, newer versions allow transfers of 4 or sometimes
even 8 bits at a time. More or less superseded by SD (Secure Digital) cards,
MMC cards are still used in devices that support SD cards because of their
cheaper cost.
RS-MMC (Reduced-Size MultiMediaCard) - Introduced in 2004, RS-MMC
cards are simply smaller MMC cards, but at about half the size: 24 x 18
x 1.5 mm. By using a simple mechanical adapter to elongate the card, an
RS-MMC card can be used in any MMC (or SD) slot.
Memory Stick - Launched by Sony in October 1998, the Memory Stick
family is a proprietary Sony format that includes the Memory Stick Pro,
a revision that allows greater maximum storage capacity and faster file
transfer speeds; Memory Stick Duo, a small-form-factor version of the Memory
Stick (including the Pro Duo); and the even smaller Memory Stick Micro (M2).
Since the format is owned by Sony, the Memory Stick is more expensive than
similar storage capacities in other open formats.
SD (Secure Digital) - Developed by Matsushita, SanDisk and Toshiba,
the SD format has been very popular, measuring 32 x 24 x 2.1 mm. However,
compatibility issues between older devices and the newer 2 GB and larger
cards and the SDHC format have caused considerable confusion for consumers.
miniSD (Mini Secure Digital) - As a removable and portable memory
card, miniSD is intended for use in cell phones, digital cameras, MP3 players
and other small portable devices, measuring 21.5 x 20 x 1.4 mm. The miniSD
card was adopted in 2003 by the SD Association as an ultra-small form factor
extension to the SD card standard. While the new cards were designed especially
for use in mobile phones, they are usually packaged with a miniSD adapter
which enables compatibility with all devices equipped with a standard SD
Memory Card slot.
microSD (Micro Secure Digital) / TransFlash - At 15 x 11 x 0.7
mm (about the size of a fingernail), microSD is a small format originally
based on SanDisk's TransFlash card format. TransFlash and microSD cards
are essentially the same, except microSD devices have the capability to
support NFC (Near Field Communication). It is about one quarter of the size
of a standard SD card but can be inserted into an adapter which allows the
card to be used in devices with an SD card slot.
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