Hi
It is certainly possible to have multiple FAT partitions on an SD card - I think that also 4 are possible using the standard partition record. I understand that even more are possible using some extension techniques which I haven’t looked into yet (I think I read something about it though).
However you are not really inquiring about FAT partitions, but more about using ‘unused’ space on the SD card for others purposes.
1) When PCs or the utFAT module partition a disk they probably try to use as much of the available space as possible. See the utFAT users’ guide example, where there are only about 3k not used on a 2G card.
2) This can however certainly be changed – there are a few values in the boot sector which inform of the partition size. If these are simply made smaller, the rest of the space can be used for other things. By using low-level access routines data can then be stored in any format (it would, for example, be possible to also have a uFileSystem part on the disc somewhere – or simply binary data… It may also be possible to increase the size of the reserved area of a single partition (this is a define) and use that for other purposes. This may be slightly riskier since I don't know whether there are any rule here about what is allowed - and data output of a partition will however not be protected and a formatting tool may even be able to be used to overwrite it with a new partition (since the data is not in any standard format it would not recognise it any allow it to be overwritten).
Regards
Mark
Regards
Mark