A 12-bit or 16-bit type FAT can be used to map a Type 6 partition because the type of FAT is based strictly on the number of allocation units (clusters), and is the same algorithm used to define the type of FAT in the OS/2 Version 1.0 operating system. FAT cluster sizes are based on powers of 2. Assuming usage of the OS/2 FORMAT utility, the minimum cluster size for a hard file is 2KB. Cluster size and the type of FAT (12-bit verses 16-bit) are determined by the media partition size. The OS/2 FORMAT algorithm is:
컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
If partition size =<16MB
then;
use 12-bit FAT; /* max 4084 entries */
max cluster size = 4KB;
end;
else; /* partition size >16MB */
use 16-bit FAT; /* max 64KB entries */
min cluster size = 2KB;
end;
컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
The actual determination of the partition type is made based on the number of clusters on that partition. OS/2 FORMAT makes sure that this is true for the <16MB and >16MB partitions.
컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
If number of clusters <= 4084
use 12-bit FAT; /* max 4084 entries */
else
use 16-bit FAT; /* max 64KB entries */
컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
A partition size of 128MB requires a 2KB cluster size, based on a maximum of 64KB allocation units (clusters). A partition size in the range of 129MB and 256MB requires a 4KB cluster size, based on 64KB allocation units. A partition size in the range of 257MB and 512MB requires an 8KB cluster size, based on 64KB allocation units.
The configuration table used by OS/2 FORMAT is show in the following table:
旼컴컴컴컴컴컴컴쩡컴컴컴컴컴컴컴쩡컴컴컴컴컴컴컴쩡컴컴컴컴컴컴컴� 쿟otal # of 쿞ize of 쿞ector Cluster �# of Root DIR � 쿞ectors 쿛artition � 쿐ntries � 쳐컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴� �32K �16MB �8 �512 � 쳐컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴� �64K �32MB �4 �512 � 쳐컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴� �256K �128MB �4 �512 � 쳐컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴� �512K �256MB �8 �512 � 쳐컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴� �1M �512MB �16 �512 � 쳐컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴� �2M �1GB �32 �512 � 쳐컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴� �4M �2GB �64 �512 � 쳐컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴탠컴컴컴컴컴컴컴� �8M �4GB �128 �512 � 읕컴컴컴컴컴컴컴좔컴컴컴컴컴컴컴좔컴컴컴컴컴컴컴좔컴컴컴컴컴컴컴�
Note: For Type 6 partitions, it is safe to use a non-default configuration, but this might be unsafe for other partition types.
The partition can reside anywhere on the media, as the primary DOS partition, or as an extended volume within the extended DOS partition. The BPB parameter number of sectors per FAT field width has been extended from a byte to a WORD, in order to define a full 128KB FAT structure. This change affects all DOS partition types.