Beginner Guide : Memory

There are quite a few different (and incompatible) memory cards used in digital cameras.

• Compact Flash (CF) - The original memory card. 42mm x 36mm x 3mm. Somewhat larger than the others, but used on all high end DSLRs. Available in capacities up to 2GB. There are also miniature hard drives (Microdrives) with almost the same form factor as CF cards (CF type II, 5mm thick)) which are available in capacities from 340MB to 4GB. Microdrives used to be cheaper than solid state CF cards, though there is not a big difference today up to about 1GB. The 4GB Microdrives are actually cheaper than the 2GB CF cards though. Of course prices change pretty fast these days! Overall CF cards tend to be cheaper than any of the other forms of solid state memory - though this too could change. CF cards and microdrives contain their own disk controller, so that makes the camera electronics simpler.
• Secure Digital (SD) - Very small - about 24mm x 32mm and 2mm thick. They have a built in write protect switch to prevent accidental erasure and certain encryption capabilities of little interest to digital camera owners.
• Multimedia - Same size as SD but with less features and no encryption capability. There are some that can be used in some SD cameras but they aren't 100% compatible with SD cards in all applications.
• Smart Media - Thinner than CF cards, but lacking an on-card memory controller. Despite the name, they're pretty dumb!
• Memory Stick - Introduced by Sony and used only by Sony(?)
• XD - Developed and used by Fuji, Olympus and Toshiba - even smaller than SD. 20mm x 25mm by 1.7mm thick

Is there any real difference in performance? No, not really. The CF cards are the cheapest per megabyte and are available in higher capacity models than the other (of course that may change with time). Most high end DSLRs use them. The smaller cards tend to be used in the smaller consumer digicams. There's really no reason to pick a camera with one type over another unless you have multiple cameras or other devices (MP3 players for example) which also use memory cards - then it's convenient if they can share cards. It may also be difficult (and/or expensive) to find really high capacity cards (1GB and up) in formats other than CF, but that's probably not a concern for most digicam users.

The following table gives the approximate number of shots you can expect to get using low JPEG compression using various pixel count cameras in conjunction with various sized memory cards at the lowest ISO speed settings of a typical camera. The exact numbers depend on how much compression the camera applies and the ISO speed used. Higher ISO settings result in more noise and noise is hard to compress and so leads to larger files and less images per card. If you're shooting in a RAW or NEF format you can divide these numbers by 3. If you're shooting TIFF files you'd have to divide these numbers by 8.

	3MP	4MP	5MP	6MP
128MB Memory	116	87	70	58
256MB Memory	232	174	140	116
512MB Memory	464	348	280	232

Approximate number of shots per memory card for various digital camera pixel counts using high quality JPEGs for storage