CF Card Question

I need to buy some additional CF cards. My current cards have a 30Mb/sec. transfer rate. However, I noticed that cards (of the same capacity) with 15 Mb/sec rates sell for considerably less. Does the transfer rate refer to the speed that the captured image is written from the camera to the card or the speed that the images on the card are written to the computer's HD when downloaded? For both?

Thank you kindly.

camera's write to an internal buffer memory and then to the card. So the faster the card write speed, the faster the camera can dump the buffer and continue to take pictures. The card speed really matters when using a camera like a 7D which can do 8fps. The camera buffer fills and the camer starts writing to the card. The faster the card write the data...the faster the camera can get back to taking pictures.

And as importantly for some, the faster the card can read, the faster you can dump the card to a hard drive. But to get the faster dump, you want a UDMA compliant reader, a faster card reader do FW800 or eSATA or USB 3.0 or being an expresscard reader for a laptop. FW400 or USB 2 will be slow.

If you only take few shots at a time, the read/write speeds may not matter so much. But if you out all day shoting large raw files at 8fps of wildlife or sports....you want big capacity fast cards, and a fast reader who is writing to a fast hard drive.

It's the maximum rate at which data can be transferred to the card. Your camera may or may not be able to achieve speeds close to that, but you'll also notice the difference when downloading the files from your card via a card reader to your computer.

MCAsan & Jon: Thank you for your clear/concise responses. I appreciate your time. Question answered.