Class speed on microSDHC/memory card: What does it do?

December 27, 2010 1:23 PM

microSDHC: Is there any difference between Class 2, 4, or 6 with regards to the speed of accessing or interacting aps/programs on a phone?

I understand Class matters for uploading/downloading data to/from the phone, but will spending more for a Class 6 microSDHC also improve mobile phone ap/program functionality?

posted by Feisty to Technology (7 answers total)

Unless the app is reading/writing to the SD card heavily, like editing video, it seems unlikely.
posted by nomisxid at 1:33 PM on December 27, 2010

It depends on what the app does. I have a 16GB class 2 card, and there's a noticeable delay on my Nexus 1 (android) phone after I've taken a picture and before it's ready to take another. Additionally, the gallery app will take some time and occasionally become nonresponsive when thumbnailing pictures.

Additionally, I use my phone as a storage drive, and it's become a PITA to move things back and forth with the waiting.

I previously had a smaller capacity class 6 card, and do not recall this being an issue.
posted by boo_radley at 1:34 PM on December 27, 2010

Best answer: Class speed indicates how many megabytes per second (MB/s) can be written to a card in a fragmented state, which should be the lowest speed a card will go. The Class directly indicates that speed: Class 2: 2MB/s, Class 4: 4MB/s, etc.

For a phone, the most you'll see is that if you are transferring files to and from the phone to a computer, mostly songs, pictures or video. In actual app usage, the limiting factor is typically your carrier's network, which is significantly slower than even a class 2 card. In other words, you won't notice the difference. The class specification is more useful when plugging said SD card (microSD, miniSD) into a camera. The amount of data written from a high resolution picture will limit how quickly you can snap pictures on your digital camera, and will have more of an effect.

All that aside, the price difference isn't that great between the classes. I'd go for a 4 or 6 based on the fact that I use my Blackberry as an mp3 player and change music every couple of weeks. Quick froogle for an 8GB microSD got me the following:

Class 2: $7
Class 4: $9
Class 6: $13
Class 10: $20-30.
posted by Mister Fabulous at 1:42 PM on December 27, 2010

Boo-radley is right- even 10 MB/s is pretty slow when dealing with any kind of media files. One of the things that makes the higher end DSLR cameras better is that they use the faster CF cards, which are up to 40 MB/s, I think.

But I'm almost sure these cards in smartphone-type devices are only for storage, not for holding application executables. So unless the app is manipulating your data on the phone, probably not faster.
posted by gjc at 2:41 PM on December 27, 2010

Faster is better for apps. Storage is fine a bit slower. Same goes with computers- fast SSD boot drive, slower HD for storing files.
posted by wongcorgi at 5:00 PM on December 27, 2010

Writing 1GB onto a 32GB class 2 microSD card takes twice as long as writing onto a generic thumb drive. Not sure if that helps or not.
posted by Hactar at 7:08 PM on December 27, 2010

I had read that class 10 micro sdhc, being relatively new, still make compromises to hit that target speed on sustained read/write operations and fall far short of that speed on random i/o, thus making them far less suitable for phone use.

The classes correspond to MINIMUM data rate. So, not only are you comparing class 2 to class 4 to class 6, but you also need to compare the brand, and that specific chip as they can vary in the faster direction.

Anecdata - I replaced a 8G class 2 with a 8G class 6 and noticed no real difference, though I secretly suspect it might be a bit slower. The android app I used is no longer on the market, but before removing the class 2 I ran a speed test on it, and it rated 2Mbit/sec (class 2 minimum) for writes, and 10Mbit/sec for reads.
posted by devbrain at 7:44 AM on December 28, 2010