Test Your Secure Digital Card: Lame and Lamer
Why Lame and Lamer? I can guarantee that the specifications of your secure digital card are bogus. As I'm fond of saying, they're blowing smoke you know where. You'll find that the read speed isn't as fast as the card manufacturer says (lame), and the write speed will typically be even slower than the read speed (lamer).
When a manufacturer like Nikon tells you how many frames you have in your camera “buffer”, they assume you have the very fastest SD card available. If you don’t have a fast card, your buffer size is much smaller. What this really means is that Nikon doesn’t have as big of a buffer as they claim; they’re depending upon your SD card to write out the pictures while you’re shooting a sequence.
I'll show you how you can test the card for yourself outside of your camera to see how fast it really is. I’m going to demonstrate results from a Windows environment; you can download other free software to perform tests in an Apple and Linux environment, as well.
The Windows program "h2testw" can measure both read and write speeds of your secure digital card. If your computer cannot take advantage of UHS-II hardware, you can't accurately assess those newer-generation cards for speed. Newer UHS-II cards have an additional row of electrical contacts on them, allowing for parallel data transmission, which is how they’re able to get so much more speed out of them.
Cameras that only have UHS-I capability can still use the UHS-II cards, but they ignore the extra row of electrical contacts and run them at reduced speed. As a result, you won’t ever get beyond the “UHS-I” speed using a “UHS-II” card.
If you use a card reader and your computer USB port is USB 3.0, then you may still be able to accurately measure it, assuming your card reader has the electrical capability of the UHS-II specification. Older computers may in fact be too slow themselves to give you accurate information, so be forewarned.
Many off-brand SD card manufacturers lie even more than the big guys. The speeds they claim aren’t even close to name-brand manufacturer speed ratings, let alone reality. Buyer beware.
Be advised that this (h2testw.exe) program will destroy any pictures on the card, so save existing pictures elsewhere before running the program. You should format the SD card once you place it back into your camera after testing it.
h2testw.exe User Interface
In-progress program screen
SanDisk Extreme Pro 95MB/s test results
SanDisk Extreme Plus 90MB/s test results
Sample computer "SD card slot" tests:
SanDisk Extreme Plus 32GB 90MB/s UHS-I card.
Actual Read speed: 69.6 MB/s
Actual Write speed: 55.2 MB/s
SanDisk Extreme Pro 32GB 95MB/s UHS-I card.
Actual Read speed: 66.5 MB/s
Actual Write speed: 67.5 MB/s
Nikon D7100 results (from cameramemoryspeed.com):
SanDisk Extreme Pro 32GB 95MB/s UHS-I card = 69.8 MB/s
The computer results and camera results are comparable to each other (within 3% for write speed). Compared to the “95MB/s” being advertised for the Pro version, however, these speeds are quite different.
Be aware that the newest SD cards (with write speeds approaching 300MB/s) are “UHS-II” or beyond. You’ll have to upgrade to a new camera (like the D500) if you expect to take advantage of such speeds.