I always assumed that the little write protect switch on the edge of a standard SD card was cutting some electrical contact inside the card so that write operations would not work at all.
It turns out though, that it doesn’t. Which means it’s basically a request to whatever device is doing the reading of it to please kindly refrain from writing to it.
And here I was thinking I could use SD cards to print photos at officeworks like a USB stick but without the risk of getting it infected with viruses. (I’d just use their email method now)
I learned this when I used the card in a USB SD card reader dongle thing, and found that I could still write to it even with the write-protect switch in the locked position!
I guess the USB SD card readers couldn’t be bothered implementing the extra logic to honour the write-protect switch.
Had one experience where a computer’s SD card reader was telling me that my card was failing (system logs attributed the errors to the SD hardware failing).
So I thought “Oh the SD card must be failing”
Thankfully I searched the errors and found a Q and A where someone suggested to just try a different reader and so I did, and it worked fine.
Had an SLR camera claim my SD card was failing, but it worked fine in the computer. I’m guessing it was because the SLR camera’s battery was almost dead, when I swapped in a fully charged one the problem disappeared!