Secure Data Cards

Secure Digital cards (SD) were originally developed by SanDisk, Matsushita and Toshiba to be used in portable devices. Today the SD is mostly used in digital cameras, PDAs, cell phones and handheld GPS receivers. As of 2008, memory capacity rages from 4MB on standard SD cards up to 32GB on high capacity (SDHC) with a theoretical 3TB SDSHC (Super High Capacity) in the works.

The format has been a widely recognized standard for portable devices. However, the newer SDHC formats have given a little confusion to consumers mainly because the new SDHCs are basically the same size and design as the standard format. The HC will still fit into older devices that do not recognize the HC format. SDHC requires that the device firmware is capable of the format, which in older devices, is not the case.

Like most flash devices, the SD cards come preformatted with the FAT32 file system. Having been preformatted at the factory allows the SD to be accessed on almost any device equipped with an SD reader. Since host devices usually read the SD as a removable drive, they can be reformatted to use any file system supported by the host device. Another feature is the standard FAT32 maintenance utilities can be used to retrieve corrupt files or repair them.

Transfer rates on SD cards are measured the same as CD-ROMs, which is in multiples of 150kB/s = 1x. Standard transfer rates for the SD are 6x the rate of standard CD-ROM. Higher transfer rates are available with the more expensive versions having speeds up to 200x. Of course in the future, even 200x is going to be considered slow. Another fact to point out is the difference between writing speed and reading speed. Maximum writing speed will always be slower than the reading speed. Nobody really needs to have a 200x speed for a camera unless they are a professional sports photographer or someone with similar application.

SD cards come in three different sizes. The standard SD measures 32mm x 24 mm x 2.1mm but can also have a profile of just 1.4mm. The miniSD, which is designed for use in cell phones, digital cameras and mp3 players, has a capacity range of 16MB in miniSD to 8GB for a miniSDHC and measures 21.5mm x 20mm x 1.4mm (approximately the size of a U.S. postage stamp). The smallest of the SD family is the microSD, which is designed specifically for use in cell phones. Capacities range from 16MB in standard microSD to 6GB in microSDHC and measures 15mm x 11mm x 1mm. Comparatively, the microSD is the size of your fingernail. All SD cards have an operating voltage between 2.7V to 3.6V and tip the scale, weighing, at the most 2 grams.

SanDisk has also come up with a new ingenious idea for connectivity. Basically the card has a built-in USB connection that exposes itself when you fold the card, negating the need for an SD reader. And one of the best features is that you can pick up an SD card for little as $10 for 4MB all the way up to $179 for a 16GB with a transfer rate of 32MB/s(200x) or 32GB with a transfer rate of 15MB/s(100x). Now we're cooking!