well, that’s just an artifact of the technology - the write speed for MLC as used in SD cards is like an order of magnitude slower than read speeds. i think the “class X” terminology guarantees some minimum write speed.
Judging by the terminology laid down in SD card - Wikipedia , look for the UHS-3 logo.
But even that is only 30 MB/s write, a far cry indeed from a hard drive or even a good flash drive Though USB sticks also tend to offer read speeds far in excess of write speeds.
It sticks out so you can remove the card. Because the SDHC slot is meant for camera cards, which you insert only for short periods. It was never meant for auxiliary storage; it connects internally to a slow USB 2.0 hub chip.
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you do realize that molex and others make SD and microSD slots with spring loaded ejectors, right? ever owned a canon camera with an SD slot? they use those kind of ejectors. whether or not they have an appropriate number of load cycles is an open question.
anyway whatever it was never meant for is entirely irrelevant. i have a 200GB microsd card in a nifty enclosure that my telescope writes images to. it’s fast enough to write 17MB files with no problem, and it doesn’t stick out the side.
lol, 17MB is the smallest weird number. well actually, no, 70 is.
not doing planetary work and so my exposures are 1200s or 1800s depending on whether or not i’m using a broadband or narrowband filter.
you’re probably writing to the buffer, which is then leisurely written to the SDCard. The problem with action photography is that the buffer fills up faster than the card can be written to. My camera, a D7000, has a 9 shot buffer, and while it can’t use the faster cards, some cards can clear the buffer a lot faster than others. None of this is advertised; rather, the companies focus on read speeds.
http://www.robgalbraith.com/camera_wb_multi_page8e34.html?cid=6007-12454
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dedicated astronomical cameras don’t have much, if any SRAM/SDRAM buffer… and my exposures are 20 and 30 minutes long. i could be writing them to a clay tablet and everything would be OK.
i’m not arguing that SD/microSD write speeds are fast. they are slow. however, the classifications do mean something; for video applications you have to be able to sustain a 5-10 megabits/sec to one of these cards. my video cameras take SD cards and unless you use a card greater than class X (whatever it is), you just can’t record more than a few seconds of video at a time. upgrade to the minimum class card and everything works as advertised.
anyway, my point is only that someone told me that the SD card slot in my macbook is not to be used as auxiliary storage, and that’s silly. it can be used for whatever the user wants, as long as the performance fits the application.
Well, I have found that most of the brands I use also post write speeds. Notably Sandisk (https://www.sandisk.com/home) and Samsung (http://www.samsung.com/us/computer/memory-cards).
I don’t really know about others, but I imagine if you search for the details, you’ll find them without too many problems (and if you don’t… , well… , that may be a reason not to buy them 
)
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