Does Class 4 perform differently from Class 6, and so on, when it comes to Micro SD(HC) memory cards on smartphones? Samsung Galaxy S to be specific.

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    This probably depends on what you're doing. Strictly speaking it would necessarily perform differently because they're different cards with different minimum transfer rates, hence why they're different classes. Will you notice on a day-to-day basis? Probably not. Will you notice if you're transferring 4 GB of files on or off the card? I'd certainly imagine so. What kind of context are we talking about when you say "perform differently"? May 23 '11 at 0:42
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    Many of the people actually running android on sdcards (ie, as /system and /data, not just for storage) seem to think that the class 4 cards may actually be faster at small operations, the theory being that the optimizations for high sustained writes on class 6 cards (presumably for HD video recording) come at a cost. May 23 '11 at 1:14
  • This is not an Android question, except insofar as Android phones use Micro SD cards.
    – ale
    May 23 '11 at 11:17
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    It is an Android question, I read about this in an article saying there's no point in getting SD Cards over Class 2 for Smartphones (Android, iPhone etc) because the smartphone hardware can't reach higher than I/O Speeds of Class 2.
    – Francisc
    May 23 '11 at 18:45

The general consensus seems to be that a Class 4 is just fine, and you definitely would not need anything faster than a Class 6. Unless you're seeing a lot of lag during IO intensive operations, though, I wouldn't be worried. The best way to test might be to take a few minutes of 720p video. If it records and plays back fine — and it should — you should be good for anything. Since L3 video at 1080p is just over 5.5 MB/s, a class 6 card is sufficient. The Galaxy S II only takes 1080p video at up to 3 MB/s, and I don't know of any phone at the moment that takes higher-quality videos.

Note that the Galaxy S uses the internal SD storage for most things (possibly including video; not sure if you can choose the save location). So the external SD card may in fact be irrelevant most of the time. I've had my Galaxy S nearly a year and used the external SD card approximately twice.

If you're copying large files onto the SD card, it will obviously take less time if the class rating of the card is higher. This might happen on file transfers from the computer, or 4G downloads with low network usage, but not during general use.

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    Is the SD card the same filesystem format as the phone's internal storage? I would have guessed it would just be FAT32 (unless you formatted it in some other way, of course). May 23 '11 at 1:02
  • @eldarerathis Ah, you're right of course. I will blame my mistake on Samsung referring to one of their internal storage partitions as an SD card :P May 23 '11 at 2:53
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    Oh right, it's one of those phones. I did always find that setup a little bit unintuitive when you can in fact have both the internal "sdcard" space and the external space... May 23 '11 at 3:42
  • Is this answer still relevant in 2014? Esp. since there are phones with 4k video out now and I believe Kit Kat allows you to run certain apps on the SD Card
    – Diskdrive
    Sep 11 '14 at 5:22
  • @Diskdrive I think the logic remains the same -- compare the bitrate of your video to the speed of your storage. Apps are not normally going to require anything near these write speeds. Sep 11 '14 at 5:29

Simply put, yes,the higher the class number the faster the performance. Prior to purchasing my class 10 32gb HD Micro SD card, I visited Samsung's support web site to see what they were selling retail for their Tab 2 tablets.While I was there I chatted with one of their techies and he stated the faster the card the better the performance so I purchased a Class 10 32gb Micro SD card from Amazon!

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    So someone from a vendor tells you that you need the more expensive model... who would have thought? Seriously, read the better answers above - figure out if you need the bandwidth or not, chances are you don't.
    – totaam
    Jan 26 '13 at 16:47

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