Digital memory cards just keep getting better and cheaper. Digital SLRs, camcorders and other multimegapixel cameras require memory cards that deliver very large storage capacity and high performance in terms of read and write speed. Noncamera applications and other digital devices—cell phones and PDAs in particular—require storage media that’s very small and thin. The memory-card industry has met and exceeded all of these requirements. Meanwhile, fierce competition among card makers for market share has kept retail prices surprisingly low.

You may or may not be able to take advantage of all of the recent advances in memory-card technology, but you can, at least, use the best card that’s compatible with your system. And you can enjoy the bargain pricing.

Physical Aspects
For the most part, memory cards aren’t interchangeable from one type to another. However, adapters that allow the one card type to fit and function in a card slot designed for another card type are becoming commonplace. For example, Sony offers two different Memory Stick adapters, one to fit CF card slots, the other to fit Memory Stick PRO.

Currently, SD (Secure Digital) is the most popular card type.

Slightly smaller than one frame of 35mm film (24mm x 32mm), SD offers high maximum capacity (2 MB) and outstanding performance characteristics. MultiMediaCards (MMC) are the same physical size and shape and will often work in cameras that were built to use SD. There are some exceptions, however, because the electrical contacts are different. The Mini SD card is much smaller—only 37 percent of the volume of an SD—and can be used in SD applications via an adapter without performance loss.

SDHC (the HC stands for High Capacity) is the latest development in the SD family and was designed to stretch the 2 MB capacity limitation of standard SD all the way to 32 MB. SDHC is not backwards compatible with SD—but you can use standard SD in SDHC host devices. In an attempt to bring some sensibility to speed ratings, all official SDHC cards are marked according to their performance class. For example, Class 2 cards (the slowest) must deliver sustained read and write speed of at least 2 MB per second. Class 4 equates to 4 MB per second. This new speed rating system makes it easier for consumers to select the right card for a particular application. However, all of the confusion hasn’t yet disappeared because some cards are capable of higher burst rates and are promoted as such.

CompactFlash (CF) has been the traditional favorite for digital SLR cameras because of its large maximum capacity, but lately it’s been losing ground to SD. CompactFlash cards are available in two styles: Type I (the more common) and Type II. The difference is the card’s thickness: Type I cards are 3.3mm thick, Type II cards are 5mm thick. You can use a Type I card in a Type II slot but not the other way around. CF+ is an enhanced version of CF that extends compatibility to wireless communications cards and other Type II devices—including Microdrives. A Microdrive is the same form factor as CF Type II but isn’t really a CF card at all. Instead of using flash memory, Microdrives store image files on a miniature hard drive.

Sony cameras use Memory Stick, Memory Stick PRO or Memory Stick PRO Duo (although the Sony Alpha 100 also accepts CF). The current Memory Stick PRO version offers high capacity (up to 8 GB) but can’t be used in some older Sony cameras.

One more type—the xD-Picture Card—is used only in Olympus and Fuji digital cameras. It’s available in capacities up to 2 GB, with larger sizes expected in the future. There are two types: Type H offers speed advantages but isn’t 100 percent compatible with type M. Check your owner’s manual or the camera manufacturer’s Website before you buy.

Capacity
Memory card prices are quite reasonable these days. There’s no excuse for not having at least a 2 GB card (higher for a D-SLR). Nonetheless, when you go on vacation, take a spare.

The number of image or movie files that can be stored on a card of a specific capacity varies so much from model to model that it’s impossible to generalize. The total is influenced by many factors, including file format (RAW files are huge), compression ratio (i.e., Fine vs. Standard) and other considerations. Best bet is to buy a card so large that you’re unlikely to fill it during one shooting session.

Speed
As mentioned above, the SDHC speed class ratings are a step toward a standardized way of understanding how cards perform in terms of sustained read and write speed. CompactFlash, on the other hand, as well as standard SD cards, is often categorized by the X factor. The same measurement method is used to rate the throughput of CD and DVD writers and works as follows: 150 KB per second is "1X" and all other speeds are expressed as multiples of that speed. For example, 80X means a write/read speed of 12 MB per second (150 KB x 80 = 12,000 KB or 12 MB). Rule of thumb: high-speed cards can capture images and play them back faster than slower cards can; though slower cards cost less and work great in everyday applications.

Accessories
Card readers are a must—no one connects a camera to a computer to download images anymore. FireWire readers are blazingly fast, although Hi-Speed USB 2.0 isn’t pokey, either. Although memory cards are surprisingly durable, the electrical contacts can become soiled or damaged—and cards are easy to lose. Keep your spare cards clean and findable in a case—not in the bottom of a gadget bag.

Kingston, a company that has developed a strong following for its PC memory products, offers leading-edge SDHC memory cards in sizes up to 8 GB and speed ratings up to Class 6. The company also offers standard SD, microSD, miniSD, MMC, CF and a line of multiformat card readers. Its 8 GB Ultimate CompactFlash offers 133X data transfer rate and comes complete with file-recovery software.

Panasonic offers a full range of SDHC cards, from entry level to professional. Available in densities up to 4 GB, Panasonic’s Pro High Speed series are Class 6 compliant, which means that they're certified to deliver a minimum sustained write speed of 6 MB per second. As a matter of fact, like Panasonic’s previous generation of premium cards, they’re capable of burst speeds of up to 20 MB per second. Panasonic has announced plans for a 16 MB card later this year.

The world’s largest manufacturer of flash memory storage products, SanDisk, recently introduced an 8 GB SDHC card—the highest capacity now available in the SD form factor. Often considered the originator of the category, SanDisk is the only company that has the rights to both manufacture and sell every major type of flash card. The new 8 GB SDHC card will hold more than 4,000 high-resolution pictures, as many as 2,000 digital songs or up to 15 hours of MPEG4 video (depending on conditions).

The new UDMA-enabled CF cards from Lexar are said to be capable of sustained write speeds of 45 MB per second when communicating with a UDMA device. UDMA is the abbreviation for Ultra Direct Memory Access. Even with conventional devices, the cards have a 300X speed rating. They’re available in capacities of 2 GB, 4 GB and 8 GB. Lexar also offers a UDMA-enabled FireWire (IEEE1394) memory card reader.

The flagship memory product from Sony is the 8 GB Memory Stick PRO Duo they introduced at the Consumer Electronics Show earlier this year. A perfect example of storage media that can be shared across multiple platforms, the PRO Duo is compatible with the PlayStation Portable, Sony Ericsson cell phones, PS3 gaming consoles and Sony camcorders.

Delkin eFilm CompactFlash memory cards are available in capacities of up to 8 GB and speeds of up to 150X. They’re popular among professionals (and serious amateurs alike) because of the extra level of quality assurance-testing Delkin performs. All eFilm cards are made in the USA.

PNY Technologies is an ISO 9001-registered international company that has been quietly building some of the most sophisticated consumer and professional-level graphics card adapters, flash memory thumb drives and flash memory cards. It offers a full lineup of MicroSD, MiniSD, SD, SDHC, xD-Picture Card and CompactFlash. Its 8 GB Optima Pro CompactFlash ultra high-speed professional memory card delivers 100X read/write performance at a list price below $200.

From Seagate, manufacturer of high-quality computer hard drives, comes a hard drive for your camera. The Seagate 4 GB and 8 GB CompactFlash photo storage drives work with any digital cameras that accept CF+ Type II cards. Despite the fact that they store data on spinning media (as opposed to solid state), they’re built Seagate-tough and are resistant to impact damage.