Porsupah said:
The issue isn't power-related. Rather, it's how the host computer implements the filesystem - the magic being the issue of caching. If you write a file to a device, be it a hard drive or SD Card, the data might indeed all be written and the file closed - but not necessarily. Depending on what other activities are going on, the changes might not actually occur until some point in the near future. This is why a sudden loss of power on most computers means the system will check the disk next time it powers up, as there's the possibility then that not quite everything was actually written out, potentially leaving the filesystem in an inconsistent state.
Thus, a "safe eject" simply ensures that everything's completed and committed, before the device is unmounted.
If you're designing a camera, you simply implement the filesystem routines such that there's never any data left uncommitted - it gets written out as soon as possible. Hence, there's no need for such a "safe eject" on cameras.
^^^ this
Properly ejecting a card ensures that all data that's supposed to be written to the device, is written before the volume is unmounted.
On the Mac, there's a bit of history involved too. In the olden days of floppy disks, Macs had powered eject mechanisms for their floppy drives - there was no hardware eject button (apart from a pinhole for emergency use). The ONLY way to remove a floppy was via the GUI software. This ensured you didn't eject the boot disk when the OS needed it, or, for the reasons outlined above, to avoid corruption of data on the volume being ejected.
Since Mac floppies were labeled by the OS from the start, it also meant you were able to copy data from one disk to another with only a single floppy drive, by ejecting the disk, but leaving its ghost on the desktop for later use even though it wasn't physically mounted. This could involve a lot of disk swapping if you were short on RAM, as it had to read the files into memory before writing them out to the target floppy. Still, it saved having to have multiple floppy drives for just occasional use.*
This carried on with Apple's built-in optical media drives (CDs, then DVDs) being equipped with motors to draw in and eject the media.
The same software eject routines and metaphor was also used for hard drives and, latterly, USB data cards and flash drives.
* IIRC DOS wasn't particularly fussy about what was in the A drive until you came to read a file. If you swapped the floppy beneath it, it could cause some problems. I stopped using it around DOS 3, so I am rather vague on the point.
How does the computer know when another card has been inserted?
