SD card partitions??? whaat???

Of course you can partition them just like any other drive. There is no special hardware that handles partitioning, it's all done on the physical disk itself.

As a single use drive, a partition table is written to the drive. The partition table relates to the type of partition you are creating. A standard FAT16 partition will only allow up to 512 entries so even if the card has plenty of space left, once the partition table holds records for 512 files no more files can be written to it. (it's true I had to find this out the hard way with a customer who couldn't save anymore work to his USB drive!!)

Formatting with Fat32 allows up to 268,435,437 files on disk (with less in folders 65,534).

So partitioning is just the way the data is stored onto the disk.

In the same manner, multiple partitions can be made. Where one references one portion of the disk and another references a separate portion.

A partitioning tool like partition magic(windows) or Gparted(linux) will help you to create, delete and modify partitions.

Sometimes it's necessary to write a disk image onto an sd card. A 2GB image file written onto an 8GB sd card will result in a 2GB sd card. It's possible to then add another partition to access the other 6GB as a separate drive. When you put and sd card with multiple partitions into your computer, the partitions appear as separate drives rather than just one.

Because of potential issues, many consumer devices like cameras will only accept sd cards with a single partition of a speceified type (usually fat16 / fat32).

Linux partitions ext2 etc... are unlikely to show up on windows.

Lucie

thanks lucie. I still don't get it how does this work in the file sistem. do you make like a special directory or something or is it just like adding another filesistem all together and if so how can you load it up since fat 32 must start from first bit of memory, is there a some sort of gateway on the begining?, and how do you prevent rewriting the other file sistem???

Martin Šalko wrote:

 

thanks lucie. I still don't get it how does this work in the file sistem. do you make like a special directory or something or is it just like adding another filesistem all together and if so how can you load it up since fat 32 must start from first bit of memory, is there a some sort of gateway on the begining?, and how do you prevent rewriting the other file sistem???

As I understand it, the beginning of a DOS disk is the master boot record: https://en.wikipedia.org/wiki/Master_boot_record#Disk_partitioning

Among other things, the MBR defines 1-4 partitions for the rest of the disk.  If you access a disk directly as sectors, there's nothing to prevent you from rewriting any of the sectors.  If you access it as a file system, the OS software prevents you from writing to the wrong partition since each partition looks like a different disk drive.

oh so it's not natively supported by the file system it self since it needs to be in master boot record?

martin

Martin Šalko wrote:

 

oh so it's not natively supported by the file system it self since it needs to be in master boot record?

As I understand it, the file system can look at a disk drive (or solid-state surrogate) as a flat array of sectors or as a set of partitions.  For example, on GNU/Linux you might have a device /dev/sda which is the entire disk and a bunch of partitions /dev/sda1, /dev/sda2, etc. which are partitions.  Users generally only see a partition, since only a partition can be mounted as a file system.  Occasionally you might look at the entire disk, for example when editing the partition table.  IIRC you must unmount all of a disk's partitions before editing the disk's partition table, which means you have to have another disk to be your file system while you're doing the editing.

thanks.