It's not very complicated, but it definitely has some screwy aspects to it. E.g., in an MBR there is a one-byte "Partition Operating System Identifier", which includes different values for things like FAT12, FAT16 small (<32MB), FAT16 large (>32MB), Extended, FAT32, FAT32 w/ VFAT, exFAT, etc.
In GPT, you still have an MBR (called a "protective MBR") in sector 0, with only one valid entry covering the entire disk and a special GPT Partition OS identifier. The "real" partition information starts with a GPT header in sector 1, and is variable-sized (depending on the total number of partitions) and generally requires several sectors. There is also another copy of the GPT (in a different "backwards" format) stored in the last several sectors of the disk. I don't know if they do it any more, but M$ (and maybe some others) were actually creating "ghost" MBR entries which corresponded to the GPT entries, and would use the MBR data instead of the GPT data. Of course, that only works if the disk has less than 4G sectors (2^32), and can also lead to problems when some utilities assume only the GPT needs to be correct while others may assume both the MBR and GPT need to agree with each other. The other major thing you should know up front about GPT is that there are no longer separate Partition OS identifiers for all of the different FATs like there is in MBR. Instead, GPT covers all of the different FATs (and also NTFS) with one ID, generically called "Microsoft Basic Data". So, in order to determine how a partition is actually formatted, you have to "decode" the Volume Boot Record (VBR) (also sometimes called a Partition Boot Record) stored in the first sector of the partition. This can lead to some interesting dilemmas when a partition has been allocated but hasn't yet been formatted (and doesn't yet have a VBR), or you want to change the format to something else. ____________________________________________________________ At long last, somebody finally built a fully functional X-Wing drone At long last, somebody finally built a fully functional X-Wing drone http://thirdpartyoffers.juno.com/TGL3141/560d5c96692465c964accst03vuc ------------------------------------------------------------------------------ _______________________________________________ Freedos-devel mailing list Freedos-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freedos-devel
