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Feature: What's Up With All Those Portable Storage Formats?

Flash memory storage devices for portable gadgets all do pretty much the same thing: store files and applications. Secure Digital, SmartMedia, and other flash memory devices have no moving parts, are small, and don't require batteries, so they're ideal for portable devices such as PDAs and digital cameras. But can differ in size, price, capacity, and other features. In addition, some (like XD Picture Card) are debuting, while others (such as SmartMedia) are exiting, stage left.

For this edition of the Mobile Computing FAQ, I've put together a rundown of the current formats, listed alphabetically. (Send your questions and suggestions for future FAQs to james_martin@pcworld.com.)

CompactFlash

Developed by SanDisk and introduced in 1994, CompactFlash is currently the most widely used flash memory card format for portable devices. CompactFlash cards weigh about half an ounce, are approximately the size of a matchbook, and are available in Type I and Type II form factors, like the PC Card format from which they were developed. (The only difference between Type I and II is that Type II cards are thicker.)

CompactFlash cards are among the least expensive flash memory formats. SanDisk's 64MB CompactFlash card retails for $50, for example, while a SanDisk Secure Digital card with the same capacity is $60. Most often, CompactFlash card slots are found in digital cameras, Pocket PCs, and some notebooks. Current capacities range from 16MB, which costs about $23, to 1GB, at about $800. The CompactFlash card's relatively large size makes it awkward for use with smaller devices.

SanDisk recently developed Ultra Compact Flash, a faster version specifically aimed at professional photographers.

Memory Stick

Launched in 1998, Sony's flash memory device was designed to store still images, digital video, music, computer data, voice recordings, and other content. Memory Sticks are about the size of an AA battery and are accepted primarily by Sony products such as camcorders, digital cameras, MP3 players, selected Clie handhelds, and VAIO notebooks. Current capacities include 16MB, 32MB, 64MB, and 128MB and range in price from about $25 (for 16MB) to about $95 (for 128MB). Memory Stick transfer rates are fairly slow, at 1.5 megabits per second.

A new format, Memory Stick Duo, is about half the weight of its predecessor and is backwards compatible if used with an adapter. Memory Stick Duo was launched in Japan in July, with no date set yet for availability elsewhere.

MultiMediaCard

Introduced in 1997, the MultiMediaCard was developed by SanDisk and Siemens. These postage-stamp-size storage devices were originally designed with mobile phones and pagers in mind, and are currently supported by such devices as the Palm M515 and the Palm I705.

MultiMediaCards have the same height and width as Secure Digital cards, which were developed later, but they're slightly slimmer and thus can't offer as much capacity. These cards will work in Secure Digital card slots, though Secure Digital cards won't work in MultiMediaCard slots. MultiMediaCards don't offer the same security as Secure Digital cards, and they aren't as fast reading and writing to disk, but they are slightly less expensive. SanDisk's 64MB MultiMediaCard, for instance, retails for $55, compared to $60 for the company's Secure Digital card. Current capacity tops out at 64MB.

Secure Digital

Developed by Toshiba and Matsushita, Secure Digital cards are nearly identical to MultiMediaCards, with several exceptions. The most important difference is that as the name suggests, Secure Digital cards offer built-in encryption to safeguard data. These cards are growing in popularity because of their tiny size and the security they offer. Currently, Secure Digital card capacities top out at 512MB. These cards tend to be a bit more expensive than other formats. For example, SanDisk's 128MB Secure Digital card sells for $90, compared to $80 for the company's 128MB CompactFlash card.

In development are several peripherals (including Bluetooth cards, digital cameras, and GPS receivers) that connect to a PDA or other device via the Secure Digital card slot.

Read more about the Secure Digital standard in our "Mighty Mini Media" story.

SmartMedia

Toshiba introduced the SmartMedia card in 1995 as the Solid State Floppy Disk Card. These cards are small, which makes them convenient for use in digital cameras and other petite portables, but their wafer-thin form factor limits storage capacity.

SmartMedia cards are priced about the same as CompactFlash cards, making them among the more affordable portable media options. Currently, SmartMedia cards are available in capacities of up to 128MB. However, this format is on its way out, as hardware makers favor newer formats such as Secure Digital and anticipate XD.

XD Picture Card

Just announced this summer, the XD Picture Card (the XD stands for Extreme Digital) was developed by FujiFilm and Olympus to compete with similarly sized Secure Digital and Memory Stick Duo cards. According to Olympus, the XD Picture Card will enable manufacturers to design smaller digital cameras and will offer higher capacities as well. The two companies plan to introduce digital cameras that use the XD Picture Card later this year.

Cards ranging from 16MB to 128MB are expected in the third quarter of this year, with a 256MB card due in December. The format has the capability to go up to 8GB, Olympus says. FujiFilm and Olympus will offer PC Card and CompactFlash adapters that allow XD Picture Cards to be used in notebooks and other devices.

For an overview of flash memory formats, see the Features Comparison chart in our "Mighty Mini Media" story.