Digital camera memory is an essential and often overlooked piece of digital photography equipment. There are many types of memory and it's a good idea to consider what type of memory a camera uses before you buy your first digital camera. It's also important to make sure you have enough memory before you take pictures of an important event or leave for vacation. Although memory cards are reusable, they don't have a limitless capacity and it's always good to have more than you actually need.

Most digital cameras come with very low capacity memory cards. If you're shopping for your first digital camera be sure to budget for an additional card. It's a safe bet that the card that comes with your camera will be inadequate. And as camera megapixel counts grow, higher capacity memory cards become necessary.

Most camera manufacturers publish tables on their Web sites and in their camera manuals to show how many images you can save on their included memory card. There’s no fixed rule for the number of photos you can put on one card because different image file types, different amounts of compression, and image content all affect the size of each file. But the manufacturer's site is a good place to start when you decide how much memory you want.

As a general rule, you should purchase at least a 256 megabyte or two 128 megabyte cards if you're buying a 3-5 megapixel compact digital camera. If you want to shoot lots of high resolution TIFF or RAW files, then you'll probably want to look at 512 megabyte and 1 gigabyte cards. It's also a good idea to not save all of your photos on one card. There's always the possibility that cards can get corrupted, lost, or stolen. Using more than one and switching during a shoot protects your valuable photographic data.

Now that you know a little more about memory cards, you can start thinking about which would be best for you.

CompactFlash
One of the most common types of digital camera memory, CompactFlash is used on most high-end digital cameras, and all digital SLRs are CompactFlash compatible. There are two physical sizes of CompactFlash - Type I and Type II. Type II is thicker and some cameras will only accept Type I CompactFlash. Type II CompactFlash is usually higher capacity. The most common Type II CompactFlash cards are mechanical, MicroDrive, memory cards.

The main benefit of CompactFlash, besides availability, is that it has a controller chip in the card. The controller chip allows higher transfer rates. Most cameras can't take advantage of this extra speed, though. Only cameras with larger internal buffers–mostly digital SLRs–can take advantage of high-speed CompactFlash. CompactFlash is inexpensive, easy to find, and works in a lot of digital cameras. For those reasons, it's one of the most desirable types of digital camera memory.

Secure Digital Cards
You’ll find Secure Digital cards, the smallest available memory cards, come with very small cameras. The current maximum capacity for Secure Digital cards is 512 MB. A variation on the secure digital card is the Multimedia card, which also has a maximum capacity of 512 MB.

xD Picture Cards
Introduced by Olympus and Fuji in 2002, the xD Picture card is the newest digital camera memory format. It's tiny size, just 0.97" x 0.98" x 0.67," means it can be used in very small cameras. The xD Picture Card can also be used in any CompactFlash compatible camera with the available CompactFlash adapter. It's currently available in capacities up to 512 MB, with larger capacity cards to be available soon. Since it was developed and introduced by Olymous and Fuji, most current compact digital cameras from those manufacturers use the xD Picture Card media.

Sony Memory Stick
Memory Stick was developed by Sony for their CyberShot digital cameras and other Sony electronic devices. With the exception of a very few cameras, Memory Stick is only compatible with Sony digital cameras. That means if you have Memory Stick media for a camera and you decide to buy another brand of camera, the Memory Stick cards you own are not likely to work with the new camera. On the other hand, if you own other Sony devices, there might be benefits to owning Memory Stick. Sony MP3 players, PDA's and selected Sony Vaio computers also accept Memory Stick media. Memory Stick is available in capacities up to 256 MB, and Sony's new Memory Stick Pro is available in capacities up to one gigabyte.

Card Readers
Card readers are the most efficient way to download your digital digital memory cards and a highly recommended digital camera accessory. Card readers plug into your computer via one of its USB ports and allow you to transfer your files without using your camera's batteries or dealing with cables. You install the card reader as you would any other USB device and plug the card into the reader when you want to transfer your images. The memory card will show up on your computer as a separate, removable drive when it's plugged into the reader. Card readers are available in inexpensive internal and external models with USB connections.