Removable Storage Devices and Cards

[Mike]

SD cards, have puzzled me for some time!

Using USB drives, I can put different sizes and they work, they
save whatever is added.

SD cards are different, if a camera says you can have a 32 GB,
that is the limit, why do they not work like USB drives and just
accept a 64 GB card and fill that up, physically they are the same
size, the contacts are in the same place, yet the camera or other
devices know that it won't save more than 32 GB.

I know that some of you are computer-literate, more than I am,
can you explain, this conundrum for me please?

Mike.

 

[Naturally]

Yeah, it’s a bit of a head-scratcher at first. The cards look the same, same size, same contacts, but the trick is in how they’re formatted and what your device understands.

So it’s a good question. SD cards look the same on the outside, but what’s going on inside is a bit different from USB drives.

The key difference isn’t the physical card, but the file system and standard the device is designed to use.

There are actually a few “flavors” of SD cards:

• Standard SD (up to 2 GB) uses the old FAT16 file system.
• SDHC (4–32 GB) uses FAT32.
• SDXC (64 GB and up) uses exFAT.

Cameras, GPS units, music players, etc. are built to recognize only one or two of those standards. So if a camera was designed back when 32 GB cards were the norm, its firmware only knows how to talk to SDHC cards formatted with FAT32. When you plug in a 64 GB SDXC card (which comes formatted exFAT), the camera simply doesn’t understand that format. It’s not a size limit so much as a compatibility limit.

A USB flash drive works differently because your computer’s operating system can handle multiple file systems (FAT, exFAT, NTFS, etc.), so it just mounts whatever it finds. A camera’s firmware isn’t that flexible.

In many cases, if the camera doesn’t officially support SDXC, you can sometimes get a 64 GB card to work by re-formatting it to FAT32 on a computer, but that’s hit-or-miss and depends on how strict the camera firmware is.

So in short: Same shape, same pins, same outside, but totally different "language" inside.

 

[timoc]

SD cards, have puzzled me for some time!

Using USB drives, I can put different sizes and they work, they
save whatever is added.

SD cards are different, if a camera says you can have a 32 GB,
that is the limit, why do they not work like USB drives and just
accept a 64 GB card and fill that up, physically they are the same
size, the contacts are in the same place, yet the camera or other
devices know that it won't save more than 32 GB.

I know that some of you are computer-literate, more than I am,
can you explain, this conundrum for me please?

Mike.

Mike, I'm useless on anything like that, I still store most things in a cupboard in jars and tins.

 

[Mike]

Thank you for the replies.

Naturally, I understand the bits where I understand the
words, some of it is way, way over my head, but I get it
that the inside is different, I only saw the capacity and
thought, "why can't I just keep filling it up, until it is full",
but your explanation has straightened my thinking out.

Timoc, yours is such a clear answer, that I understood
immediately, it didn't tell me a lot about HD cards, though.

Thanks again.

Mike.