A Primer On Memory Cards; Sometimes You Need A Memory Card Scorecard Before You Buy

The man at the discount store carefully examined every item on the rack, pulling each forward while scrutinizing it with squinted eyes. “It’s harder than finding the right watch battery,” he said under his breath. “There are plenty to choose between, but which is the right one?”

I found out later he was looking for a high-capacity SDHC card for his shoot-and-share mini camcorder. He left empty-handed. Like many people, he was confused by too many choices. Who could blame him? With that in mind, here’s a rundown of card types and classes.

Secure Digital (better known as SD) in all of its permutations, including its high-capacity cousin SDHC, are the most popular card types. Slightly smaller than one frame of 35mm film (24x32mm), SD offers reasonably high capacity (2GB maximum) and outstanding performance characteristics. SDHC uses an improved internal architecture to stretch the storage limits all the way to 32GB. MultiMediaCards, also known as 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 miniSD card is much smaller—only 37 percent the volume of an SD—and can be used in SD applications via an adapter without performance loss.

The microSD card is smaller yet, and more commonly seen in devices like cell phones and GPS navigators. The microSD may prove ultimately to be the universal storage media because—with the right adapter—it can be used in SD, xD-Picture Card, and some Memory Stick PRO Duo applications, as well as a wide assortment of non-photographic devices. For example, one can buy a Kingston 2GB microSD card with a full-size SD adapter for less than $15. And Olympus includes a microSD-to-xD-Picture Card adapter with popular cameras such as the Stylus 1030 SW.

The improvements offered by SDHC come with baggage. SDHC is not backward compatible with SD (although you can use standard SD in SDHC host devices). And you’ll need a USB 2.0 SDHC card reader to enjoy the benefits when downloading.

On the positive side, in an attempt to clarify and standardize read/write 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 speeds of at least 2MB per second. Class 4 equates to 4MB per second. This new speed rating system makes it easier for consumers to select the right card for a particular application, particularly video recording. However, all of the confusion has not yet disappeared because some cards are capable of higher burst rates and are promoted as such.

In addition to the observable improvements, there are hidden ones. Before the advent of SDHC, cameras could not determine the storage conditions inside the card when writing data. Writing speed is heavily dependent on card fragmentation. In other words, the availability and arrangement of empty storage space greatly influences write speed. Now, with the new classification system, a properly equipped camera can check the fragmented state in the card and calculate the write speed at every storage location. This means it can determine where to write the data according to its speed requirement. Not only can SDHC run fast, it can look where it’s going.

CompactFlash: Types And Speeds
Onetime ruler of the roost, CompactFlash, or CF, isn’t going away any time soon. It remains the traditional favorite for D-SLR cameras because of its large maximum capacity, despite the inroads being made by SDHC. CompactFlash cards are available in two styles: Type I and, although you’ll seldom see them, Type II. The difference is the card’s thickness. Type I cards are 3.3mm thick and 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 CompactFlash 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 CompactFlash card at all. Instead of Flash memory, a Microdrive stores image files on a miniature hard drive.

The speed classifications commonly used for CompactFlash are not as straightforward as the speed class system that’s in place with SDHC cards, so it’s much harder to gauge actual performance. Some companies use exciting names to suggest speed and power, while others revert to the old “X Factor” that’s left over from the computer world. Some combine both to create even more confusion. The X Factor is the same measurement method that’s used to rate the throughput of CD and DVD writers and works as follows: 150KB per second is “1x” and all other speeds are expressed as multiples of that speed. For example, 133x suggests a sustained write/read speed of 20MB per second (150KB x 133 = 20,000KB or 20MB). In some cases, however, this is the potential speed, not necessarily reality. General rule of thumb: High-speed cards allow you to capture images and play them back faster than is possible with slower cards. Slower cards cost less and work great in everyday applications.

And There’s More…
Sony cameras use Memory Stick, Memory Stick PRO, or Memory Stick PRO Duo (Sony’s flagship Alpha 700 also accepts CF). The current Memory Stick PRO version offers high capacity (up to 8GB) at prices comparable to other types of media but cannot be used in some older Sony cameras.

The xD-Picture Card is a brand-lock product used only in Olympus and Fuji digital cameras and some Olympus audio recording devices. Maximum capacity currently available is a scant 2GB, although larger sizes have been rumored for some time. Within the format there are two variations: Type M and Type H. Type H offers speed advantages but is not 100 percent compatible with Type M. Check your Owners Manual or the camera manufacturer’s website before you buy.

Card Buying Tips
Once you’ve figured out exactly which type of card you need, how do you decide which one to buy? Here’s my advice: The single most important attribute is reliability. It doesn’t matter how much money you save when you buy a memory card if all you have left at the end of the day are memories—and no images. Stick with a well-known brand. Second, within the speed classification that your shooting habits require, buy the largest capacity card you can afford. Some folks believe that a larger card, like a 16GB CF for example, is more fragile than an 8GB or 4GB card. Rubbish. Buy a big card—next year it will seem like a small card compared to the other cards that will be on the market by then.