I have been searching for fast memory cards for my DSLRs and my Point & Shooter. the reason is twofold. 1. I want more than 2 g of space on the card in my little Canon SD780. 2. I will probably be going to Haiti soon to shoot stills of the efforts of our biggest client, DRC, in removing bodies and debris from several sites and I want cards with high capacity AND fast writing speeds. Before leaving on such an assignment I always charge up all the batteries involved but this time I want to be able to shoot even more rapidly than usual. I'll probably be in and out in one day and want my shooting to be as efficient as possible. If you've ever looked at your LCD to see a shot you just took and seen the word BUSY on the screen then you've been waiting for your camera to write the files to your memory card. I'm hoping a high speed card will allow the camera to write those files a quickly as the camera can.
I decided to look in to the meanings of the speeds shown on the labels of the cards at which I looked. I noticed that some cards were rated with a multiplying factor such as 133x and others were rated at megabytes per second such as 30mb/s. The most informative article I found was in Wikipedia so it's based on input that isn't necessarily professional but the information matched up nicely with several other sources that didn't lay the information out as well.
It seem that the multipliers are based on a base transfer rate of 150kb/sec which was established some time ago in the infancy of the medium. So the speed of 133x on my Lexar 8gig card means a write speed of just under 20mb/sec. That means that the SanDisk card I saw advertised with a write speed of 30mb/sec is faster. File size and the camera you're using will make a difference so, as usual, the speed ratings are kind of arbitrary and just an index. Here's a nice chart that I saved to translate one speed rating in to another.
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