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About Memory Cards
While in the past, many companies (particularly SanDisk) used their own proprietary formats for data storage, memory card formats for digital cameras are now very standardized. In general, you can buy a card made by any manufacturer to use in any camera, as almost every digital camera now accepts either SD or CF cards, if not both. Let's look at some of the factors you might consider in choosing a memory card.
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What are CF and SD Cards?
Compact flash memory cards, which were developed by SanDisk in 1994, are generally used for storing photos in DSLRs, particularly professional-grade cameras CF cards come in two types: microdrive cards (which essentially contain a small hard drive) and solid state cards. Generally solid state ones are tougher and draw less power. At the time of this writing, most CF cards hold between 1 gigabyte and 32 gigabytes, although several 64 gigabyte cards have been introduced over the last few years.
SD (Secure Digital) cards, on the other hand, all have solid state memory. As they have a 9 pin interface rather than the 50 pin interface found on CF cards, they have a lower maximum transfer speed. Additionally, a standard SD card holds a maximum of two gigabytes of data; however, SDHC (SD High Capacity) cards have the same physical size and can hold up to 32 gigabytes.
Both CF and SD cards have persistent memory, which means that you don't lose your photos when you stop supplying the card with power. Memory cards for digital cameras are designed to be very reliable, as photographers depend on them!
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Memory Card Speed
When looking at the stats of your memory card, transfer rates will be listed as something like 100x or 400x, where x is 150 kilobytes per second. As your camera has a limited amount of internal memory, a faster card means less time to clear the camera buffer and take more photos.
However, don't forget to look at the maximum transfer speed of your camera as well! There's no point in paying extra to get a 400x card rather than a 200x card if your camera can only write data at 150x anyway! The transfer speed is most important if you'll be shooting continuously; if you're taking multiple photos per second, your buffer can fill up fast, but if you're doing landscape photography it's probably not as important.
Of course, a higher speed means less time spent transferring the photos to your computer or electronic storage device as well! If you'll fill your cards quickly, it may be worth investing in a faster card simply so you can cut down on the time it takes to back up your photos and get the card ready to use again.
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Memory Cards for Digital Cameras: Does Size Matter?
How large of a memory card do you need? A few years ago, a one gigabyte card was considered quite large enough; these days, 16 GB cards are popular and the recently introduced SDXC standard will allow cards to hold up to 2 terabytes!
Some of the trade-offs are obvious: smaller cards are cheaper! If you have a limited budget, buying a larger card may mean settling for slower transfer rates.
Ignoring the money issue, the advantages of a larger card are obvious: you don't have to swap cards as often or worry about running out of space during a long day of shooting. You also don't have as many things to carry; if you're using a half-dozen memory cards, it's much more likely that you'll get them mixed up or lose one than if you only have one or two. You also put more wear on the camera door changing cards more often.
Of course, the flip side of that is that when you have more cards, if one of them fails, you lose fewer photos. You may also be able to get the same amount of space for less money; two 32 GB cards will generally cost a lot less than one 64 GB card!
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Choosing a Memory Card
Ultimately, when it comes to memory cards for digital cameras, which camera you have will most likely determine which type of card you need to use. Of course, a few cameras do take both types...but generally in that case you would use both at once!
Modern memory cards are fairly reliable, and as long as you protect your memory card, it's unlikely to fail anytime soon, although you should back up your photos regularly and format your memory card occasionally to avoid errors. (The author's engagement photos were almost lost due to memory card failure once, most likely due to lack of formatting; consider yourself warned!)
So which card should you choose? As long as it can read data as fast as your camera can write it and can hold as many pictures as you're likely to ever take in any one session (where a session, in this context, means however long it is until you back up the photos and wipe the card), pretty much any compatible card should work. Now go take some photos!