Terminology

Many of today's latest phones, handheld games, and digital cameras use flash memory cards for storage. Choosing which card to purchase can be daunting because there are so
many options. This article will discuss several of the most popular forms of flash memory storage so that you can make an informed decision.

A Secure Digital, or SD card, is a type of flash
memory that is popular in today's portable devices. It can come in capacities from 8 MB to 32 GB. This format has proven to be wildly popular for several reasons. Its compatibility with a
large number of devices is one of the primary factors. Gaining the ability to easily add extra storage space to several of your gadgets with a single card has also been a source of its
continued success. The SD card's tiny size (24x32x2.1mm) makes it easy to transport. SD cards also ship with Content Protection for Recordable Media (CPRM), a copyright
protection technology, which enables a secure distribution system for all types of commercial media. The SD card is already supported by more than 600 companies around the world and on
it is way to becoming the standard memory card for digital connectivity. SD cards also enjoy the widest compatibility amongst devices.

SDHC (Secure Digital High Capacity, SD 2.0) is an extension of the SD standard that appeared in June 2006. SDHC allows standard-compliant capacities in excess of 2 GB.
SDHC cards are often formatted with the FAT32
file system. It uses the same form factor as SD, but the SD 2.0 standard in SDHC uses a different memory addressing
method (sector addressing vs byte addressing), thus theoretically reaching a maximum capacity of up to 2 TB (2048 GB). However the SD Card association have artificially defined the
maximum limit of SDHC capacity to 32 GB. SDHC cards only work in SDHC compatible devices, but standard SD cards work in both SD and SDHC devices. The SDHC
trademark is licensed to ensure compatibility.

SDHC cards have SD Speed Class Ratings defined by the SD Association. The SD Speed Class Ratings specify the following minimum write speeds based on
"the best fragmented state where no memory unit is occupied":

• Class 2: 2 MB/s


• Class 4: 4 MB/s


• Class 6: 6 MB/s

SDHC cards will often also advertise a maximum speed (such as 133x or 150x) in addition to this minimum Speed Class Rating. See section
Speeds above for a further explanation. One critical difference between the Speed Class and the maximum speed
ratings is the ability of the host device to query the SD card for the speed class and determine the best location to store data that meets the performance required. "Maximum speed"
ratings are quoted by the manufacturers but unverified by any independent evaluation process.

SD and SDHC cards and devices have these compatibility issues:

• Devices that do not specifically support SDHC do not recognize SDHC memory cards.


• Some manufacturers have produced 4 GB SD cards that conform to neither the SD2.0/SDHC spec nor existing SD devices.


• File System: SD cards are typically formatted with the FAT16 file system, while SDHC cards are typically formatted as FAT32. However, both types of cards can support other general-purpose filesystems, such as UFS2/ext2 or the proprietary exFAT for example.

The miniSD card was adopted in 2003 by the SD Association as an ultra-small form factor extension to the SD card standard. They come in
sizes from 16 MB to 4 GB. While they were specifically designed for use in mobile phones, they often come packaged with a miniSD adaptor for use in standard SD card slots.

A
microSD card is currently the smallest memory card format available. About the size of a fingernail (15x11x0.7mm), the microSD card is truly a marvel of engineering.
Even though the card is tiny, you don't have to sacrifice in capacity. microSD cards come in sizes up to 32 GB. They can also be inserted into an adapter which will allow them to be
used in any device with an SD card slot.

The MultiMediaCard (MMC) is another type of flash memory for use in a wide variety of devices. Originally created in 1997 it used a 1-bit
serial interface. The latest iterations now offer transfers of up to 8 bits at a time. While often eclipsed by SD cards, MMC cards are still popular due to their compatibility and less
expensive prices. Measuring 24x32x1.4mm the MMC card is about the size of a postage stamp, and comes in capacities up to 8 GB.

MMCplus and MMCmobile
The version 4.x of the MMC standard, introduced in 2005, brought in two very significant changes to compete against SD cards. These were
support for running at higher speeds (26MHz, 52MHz) than the original MMC (20MHz) or SD (25MHz, 50MHz) and 4 or 8 bit wide data bus.

Version 4.x full-size cards and reduced-size cards can be marketed as MMCplus and MMCmobile respectively.

Version 4.x cards are fully backward compatible with existing readers but require updated hardware/software to use their new capabilities; even though the 4 bit wide bus and high-speed modes of
operation are deliberately electrically compatible with SD, the initialization protocol is different, so firmware/software updates are required to allow these features to be enabled
when the card is used in an SD reader.

CompactFlash (CF) cards are a slightly larger form of flash memory. First appearing in 1994, the format is used in a handheld and laptop computers
and digital cameras.  There are two varieties of CF cards, Type I, and the slightly thicker Type II. CF cards have benefited from their large capacities, up to 32 GB, and until
recently they also had superior cost-to-memory-size ratio relative to other storage formats. By using a plug adaptor, CF cards can be used in standard PC Card slots. Making use of a
card reader will allow you to transfer files to or from any device with USB or FireWire ports. While CF is one of the oldest formats, it is also on of the most popular do to its wide
use in the professional camera market. CF is among the oldest and most successful formats, and has held on to its niche in the professional camera market especially well.

The extreme Digital (xD) Picture Card is another form of flash memory primarily used in digital cameras. Introduced in 2002 xD cards are used in Olympus and Fujifilm cameras. They are
available in sizes from 16 MB to 2 GB and measure 20x25x1.7mm. The XD cards were the smallest on the market until the Mini SD card was announced in 2003. XD cards are faster in comparison
with other formats such as SmartMedia and MultiMediaCards, but slower than its main competitor, SD cards. While they are generally more expensive than other formats, they have low power
consumption and their small size allows devices to be smaller as well.

Memory Stick is a flash memory format launched by Sony in1998. The name is used to describe the entire line of Memory Sticks including the Memory Stick PRO, Memory Stick Duo,
and Memory Stick Micro. They are available in sizes up to 16 GB and are primarily used in Sony and Sony Ericsson devices.

Memory Stick PRO DUO cards have a High Speed mode which allows for faster transfers. The PRO Duo cards have a
smaller form factor, and were created for use in Sony's PSP gaming device. Using an adaptor allows the cards to work in devices that only accept the larger form factor. These are available
in sizes up to 16 GB.

USB flash drives are memory devices that use a USB interface. They can effectively replace other forms of storage such as hard drives, CD-ROMs or DVDs.They can store
an incredible amount of information and can be easily slipped into a pocket, or attached to a keychain. The ability to have important files available whenever you need them has played a
large part in their success. By using a USB flash drive you no longer have to burn a CD or DVD to transfer files from one computer to another. They can be used on virtually all
computers and this compatibility extends to other peripherals and devices as well. Many USB flash drives come with a password protection system to eliminate fears of ones data
being compromised. Now that they are available in sizes up to 64 GB, it has basically become possible to keep your hard drive with you.

A card reader is a device with a USB interface that is used to access the information of memory cards. They offer an easy way to
transfer your digital images, music or data right to your computer. There are card readers for each different type of memory card, and some readers accept more than one type. They come
in various sizes, from a Bluetooth dongle that accepts a single card, up to multi readers that can accept 23 different cards. If you deal with memory cards on a regular basis, a card
reader is a necessity.