Clearing Up SD Memory Card Confusion

The SD memory card has come to dominate the world of digital cameras, both still and video, and it’s even made it way into recent Macs and many Android tablets. This is the story of the card’s origin.

Transcend 1000x CompactFlashThe world of flash memory cards has never been a simple place. CompactFlash arrived in 1995 and remains the capacity king to this day, primarily because it’s physically larger than any of its competitors at 43 x 36 x 3.3 or 5.0 mm. The highest capacity cards at present are 256 GB with bigger cards on the way, and CompactFlash cards come in very high speeds. This is the card you’ll find in most pro photo gear.

SmartMedia was its first stiff competition, introduced the same year. It had a slightly larger footprint at 45 x 37 mm but was only 0.76 mm thick. The biggest drawback is a maximum 128 MB capacity.

The SD Family Tree

MMC *(MultiMediaCard) arrived in 1997, offering a physically smaller memory card – the same size as the later SD card. Capacities of 128 GB are available, but when Secure Digital (SD) arrived, it quickly displaced MMC and soon left SmartMedia in its dust.

2 GB Class 4 SD card

2 GB Class 4 SD card.

The problem with SD is that the original standard, also known as SDSC, specified a maximum capacity of 1 GB, which didn’t seem like a big deal turn of the millennia. More recent cameras and other gear designed for SDSC is often able to use 2 GB and 4 GB cards, but most earlier SD devices cannot use more than 1 GB of storagee.

Boosting capacity beyond the original specification, SDHC (high capacity) supports up to 32 GB of storage, and when that wasn’t enough for some users, the industry released SDXC, which can theoretically support 2 TB (2,048 GB). 64 GB seems to be the highest capacity card currently announced.

There are also different sized cards in the SD family. miniSD measures 21.5 x 20 x 1.4 mm (vs. 32 x 24 x 2.1 mm for full-sized SD), and microSD reduces size to 11 x 15 x 1.0 mm. There are also higher capacity variants: miniSDHC, microSDHC, and microSDXC.

We have three capacity families (SD/SDSC, SDHC, and SDXC) and three form factors (SD, miniSD, and microSD).

Where CompactFlash cards were usually marketed as being so many times faster than a standard CD-ROM player, SD are now marked using a “class” system: Class 2 means a minimum 2 MB/s write speed (roughly equal to 13x), Class 10 means 10 MB/s (67x), and so on.

Other Competitors

Sony chose to go proprietary with its Memory Stick, which the rest of the industry almost completely ignored because it was about the same size and shape as a stick of chewing gum. And like SmartMedia, the original standard topped out at 128 MB. Despite many modifications, Memory Stick remains something only Sony seems interested in using.

As SmartMedia ran out of steam, several companies that had backed it created a new type of card rather than adopt the nearly ubiquitous SD card. The xD Picture card is about 2/3 the size of SD and handles up to 512 MB of memory, four times as much as SmartMedia. The later Type M xD card supports up to 2 GB, as does the faster Type H xD card.

USB Flash Drives

The biggest competition to the SD card family is the ubiquitous USB flash drive (a.k.a. thumb drive). The first appeared in 2000, and today you can get them in USB 2.0 and USB 3.0 versions, with capacities should reach 1 TB by the end of 2013.

Most USB flash drives are fairly large, and you won’t see them used in digital cameras, but they have replaced floppy disks, Zip disks, and burnable CD and DVD discs as the device of choice for moving data between machines.

Keywords: #sdcard #sdmemorycard #sdhc #sdxc

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