A question I get often is “what memory card speed do I need”. The ratings are confusing and the offering even more so. So this is a good question. A reason to explain card speeds.
I have explained before why and when you need fast cards (in short, when you shoot high-def video, when you shoot sports, and when for simple convenience you want to be able to review the pictures on the back of your camera as quickly as the camera will allow).
But what do the ratings mean?
- CF Card ratings. The original CD-ROM had a transfer rate (“how fast can data be moved off the device?”) of 150 kByte/second. That is what we call “1X”. So 10x = 1.5 MByte/second, and “40x” means “6 MByte/second”. This is how CF cards are rated.
- CD card ratings. These are usually rated as a “Class”. This expresses the minimum transfer speed in MByte/sec, so class 6 means 6 MByte/second.
- Manufacturer ratings. Oh, well, these are mainly (but not all) marketing. “Extreme this or that”. You need to Google these and translate them back to real numbers.
Be aware of a few things.
- Just like Megapixels, a simple number does not tell the whole story. Is the data rate continuous or “burst”? Does the card do more error-checking and correcting while it is doing the transfer?
- And be weary of large sizes: if you lose a 16 GB memory card due top failure or theft, you lose hundreds or even thousands of pictures all at once.
Michael’s tips: Buy a few good brand-name memory cards (Sandisk and Lexar are the class leaders). Own at least one fast card. For hi-def video, you need a class of at least 6 (6 Mbyte/sec).
“CD card ratings” s/b “SD card ratings”.