The two main formats of cards are SD and CF, and these are the ones we will mainly be referring to. Other formats include SmartMedia, Memory Stick (+ MS Duo, Pro Duo), Mini and Micro SD, XD, and MultiMedia. A few months ago, the XQD format was also announced although they have not been made available quite yet and the Nikon D4 is the only camera currently to support the format.
Compatibility and Error Codes: There are constantly new memory cards coming out on the market and one big issue that we see frequently is people who have older models of digital cameras, and try to buy newer memory cards. If your card is not compatible with your camera, you may get a “card error”, or general error message. Card error codes can mean a variety of things from card full, bad card, card needs to be formatted, or card not compatible. Each camera brand has their own set of error codes. Here are a few of the more common ones-
FULL (blinks): Memory insufficient to record further photos at current settings, or camera has run out of file or folder numbers.
CHA (blinks): Error erasing memory card or unable to create new folder. Also shows up as message: "This memory card cannot be used. Card may be damaged. Insert another card."
-E-: Camera cannot detect memory card.
For (blinks): Memory card has not been formatted for use in camera.
Other error messages: Memory card is write protected, This card cannot be used, This card cannot be read, Card is not formatted, Out of memory, Image cannot be saved, Sound file cannot be saved, Cannot record movie, and Memory contains no images.
ERR 02: There is a problem with the memory card. Reinsert/change card or format card with camera.
ERR 03: Too many folders in the memory card. Replace with a formatted card.
ERR 04: The memory card is full. Replace memory card.
Other error messages: No memory card, card locked, cannot record, memory card error, memory card full, and protected!.



Another possibility is to receive no error message at all. Sometimes the card may seem to work fine, but then patches of pixelation appear in the first part of a video file which looks like card corruption.
A few things to keep in mind is if it's an older digital camera (more than a few years old), to stick to cards under 2 GB (FAT 16 cameras can only accommodate cards up to 2GB. To exceed 2GB, you need a camera that formats to FAT 32). Some of the really early digital cameras may not even work with cards 1 GB or larger, so be sure to check the time frame that your camera was produced and look up any card compatibility issues before purchasing a new memory card with more capacity. Often customers think that the camera is broken, when really the card is too large to use with that particular camera.
A few cameras, such as the Nikon D7000 have a Firmware update (1.03) that is available to address the high capacity SD card compatibility issues.
More information on memory cards...
SD (Secure Digital) cards have a storage capacity of 2 GB and less, and come in various speeds indicated by a “Class”. The least expensive or older cards may not show a class designation, and they are usually a Class 2. A Class 6 card is the minimum that should be used when shooting digital video. A Class 10 card should be used with High Definition video. The difference in the classes indicates the speed at which the card can handle information. Even if you are not doing video, the faster speeds will transfer to the card in a camera and transfer information to the computer faster. An SDHC card is adding High Capacity to the type. The storage capacity for these cards is more than 2 GB, up to 32 GB.
SDXC cards are the same size as the SD and SDHC cards, but will attain extreme capacity. The next-generation SDXC memory card specification dramatically improves consumers’ digital lifestyles by increasing storage capacity from more than 32 GB up to 2 TB. Its exFAT file system handles large volumes of data. The specification for increasing bus interface, "UHS-I," with speeds up to 104 MB per second and a road map to 300 MB per second, and UHS Speed Class are available for SDXC cards and host devices. SDXC's extended capacity will provide more portable storage and speed, which are often required to support new features in consumer electronic devices, mobile devices, and industrial devices. As a general rule, these devices can use the listed types of memory cards- SDXC devices can use SD, SDHC and SDXC memory cards. SDHC devices can use both SD and SDHC memory cards. SD devices can only use SD memory cards.
CF (Compact Flash) cards are primarily used in Professional grade SLR cameras. As with the SD memory, if you are going to shoot HD video, you need a high speed card. A 400X speed card can read at 90 megabytes per second and write at 30 megabytes per second. A 600X speed card can read and write at 90 megabytes per second. These are necessary when shooting 1080 resolution HD videos, plus transfer to your computer will also be very much faster.


the inside of an SD card


Card health and formatting: Memory cards are quite sturdy and commonly expected to work through one million read/write/erase cycles. The weakest part of the card is the connectors however, and should withstand around 10,000 insertions/removals into a camera or card reader.
No matter which type of card (CF I&II, SD, XD, SM, MS, etc.) your camera takes, it's a good idea to format it on a regular basis. While it may not happen often, these little cards of information can fail and reach the end of their life unexpectedly. To keep your card in good health, format it in the camera from time to time. (I format my card after every major download, not every download, just every major one where the card has been filled or almost filled). This clears up the card and erases all of the data. Of course make sure that you have downloaded and saved onto a computer all of the files on the card before formatting. Some older cards and cameras may also show error messages if the card is not properly formatted to that camera.
How to format- Each camera menu is different, but you can typically find the formatting function in one of the last sections in your menu (usually marked with a wrench symbol & yellow in color), and also in the menu when you're in "playback" mode. If you can't find it, refer to your user manual. All you have to do is select "format" and hit your enter or set key, and confirm.
A few other things to remember about cards- it's best to keep them in their little plastic cases when not in the camera body. This protects the small connection holes/contacts that transfers your data from camera to card, card to computer, and protects the shell of the card itself.
Also when putting in and taking the memory cards out of the card slot, both in a camera and in a card reader- be gentle and don't force it. Putting too much pressure on the card can cause damage, as well as causing damage to the pins that are in the camera or card reader. If the pins get bent too many times the pins can also break off.



Card readers:  The most efficient and reliable way to download your digital information is by way of a card reader. Why use a card reader instead of just plugging your camera into the computer to download? It's a safer transfer, downloads faster, takes up less space on your desktop, doesn't need batteries, does not use the cameras battery power, and you don't have to dig for the correct connection cord. They are inexpensive and plug directly into your computer via USB or FireWire.
Another Resource: The CF/ SD Performance Database is a great compilation of write and read speed test results designed to aid the photographer in selecting camera storage media for a Canon or Nikon digital SLR's. While all camera models are not listen (and most of the older ones aren't), they still have a pretty nice list of cameras and test results that you may want to reference.