Before you read on: This guide is several years old, please read our new version, updated August 2010!
The digital equivalent of film, removable memory cards, are what digital cameras use to store the images they have taken. The size of commonly-used memory cards is measured in megabytes (MB), and depending on the size of the card and the format of the images saved on it, a card can hold anywhere from one to many hundreds of digital images. When a memory card is full, the camera owner can either delete images from the card or transfer them to a computer or storage device to free up space for additional pictures.
The vast majority of digital cameras come standard with memory cards (often 16MB or 32MB) that are far too small for the active photographer. Cameras are capable of saving images in a variety of formats and resolutions, and Digital Camera HQ strongly recommends that owners purchase a memory card that can store at least 100 images in the highest quality Joint Photographic Experts Group (JPEG) format, the most commonly used image file type.
Look for Digital Camera HQ's Recommended Package information for each camera to see the included memory card's capacity and our minimum recommended memory card size. Advanced photographers intent on shooting and editing the highest quality images possible should purchase higher-capacity memory cards to accommodate the much larger uncompressed RAW and TIFF image files.
There are several memory card formats available, including CompactFlash, Secure Digital, Memory Stick, SmartMedia, MultiMedia Card (MMC), and xD Picture Card. With the exception of the few cameras that can accommodate two types of storage device, digital cameras requires a specific memory card format and are not compatible with any other type of memory card.
The different formats offer comparable image quality, though they vary in speed and available memory. CompactFlash is currently the most popular among camera manufacturers and is also available in the largest size - up to 2 gigabytes! With the recent advent of xD cards by Fuji and Olympus, it appears that SmartMedia format may be on the decline, but keep in mind that it is hard to make the wrong choice of formats, unless one plans to swap the memory card from a digital camera to a future device like a digital video camera or a digital music player.
If all other factors are even, Digital Camera HQ recommends that consumers buy a digital camera that uses non-exclusive memory card formats (Sony's Memory Stick is a proprietary format that works with Sony and just a few other brands) to reduce the chance of getting 'stuck' with a format that may not be supported in the future. For a detailed description of memory card formats, we recommend B&H Photo's essay: What is a Digital Memory Card.
Some memory card manufacturers, including SanDisk, Lexar and SimpleTech, are releasing new models with higher speeds. These cards are more expensive, but for some photographers they're worth the price, because it takes less time for the image to be sent to the card - and so shot-to-shot time can be reduced. While the casual photographer may not notice the difference, this speed is crucial for photographers who take live-action shots in continuous mode - like at a sporting event, for instance.
Memory cards are produced by a number of different companies, including the camera manufacturers themselves. Price is dictated by the brand and speed of the card, but don't feel obliged to buy the most expensive card, as long as the format is correct and the card has a one-year warranty.
High speed memory cards that record data more quickly and allow faster shot-to-shot times are available at some retailers - if speed is a concern, and you can spare the extra money, look for Lexar high speed cards, SimpleTech ProX cards, or SanDisk Ultra cards, which offer substantially faster speed than standard memory cards.
The price of memory is falling by the day, however, and should continue to do so, making even large-capacity cards available to the budget-conscious consumer.
Recommended Accessory: Memory Card Reader
A related accessory that digital camera owners find to be very useful is a memory card reader. Memory card readers, some of which are available for less than $30, plug into your computer and let you transfer images from a card without connecting your camera to the computer. This allows for much faster image download times and simpler operation. Owners of laptop computers can even buy a card reader that will slide directly into their PC card slot.