SD cards (secure digital cards) have become preferred memory cards for a large section of small electronic devices, including cameras, cell phones, PDAs and various media players. Ranging from 16MB to 2TB, there exists an ever-changing number of SD types regarding memory space, speed and size.
Brands
Some of the largest SD card producers are SanDisk, Matsushita, Toshiba, Kingston, Panasonic, Sony, Pretec, OCZ, PNY and Transcend.
Memory Space
Regular SD cards have a storage capacity of 16MB to 4GB, while SDHC (secure digital high capacity) cards run from 4GB to 32GB.
SDXC
SDXC (secure digital extended capacity) is the newest released SD technology that bumps the maximum storage capacity from 32GB to 2TB (2048 GB).
Speed
Measured like CD-ROMs, speed grades for SD cards are written in multiples of 150 kB/s. Low-speed cards run as slow as 6x, or .9MB/s, while high-speed cards such as SanDisk's Extreme IV can read at 300x, or 45 MB/s.
Size
In addition to regular postage stamp-sized SD cards (24mm x 32mm x 2.1mm), there are micro- and mini-SD cards used less frequently in select products.
Compatibility
While almost all producers of SD-using devices adopted the SDHC SD2.0 standard, some have still manufactured SD cards that do not conform. Be sure to check products for compatibility issues before buying. All SDHC devices will work with SD cards, but the opposite is not always true.
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