Contiguous Allocation

It requires that each file occupy a set of contiguous blocks on the disk.Disk addresses define a linear ordering on the disk.Contiguous Allocation of a file is defined by the disk address and length of the first block.If the file is n block long ans starts at location b,then it occupies blocks b,b+1,b+2,...,b+n-1.The directory entry for each file indicates the address of the starting block and the length of area allocted for this file.

Linked allocation

The information of a file is stored in several non-contiguous physical blocks, each of which is connected by a pointer, and the previous physical block points to the next physical block.This method can improve disk utilization and is convenient for file deleting and inserting.

Indexed Allocation

Each file has a primary index in the FAT, and the index contains the entry for each partition assigned to the file. The index of the file is stored in a separate block, and the entry to the file in FAT points to this block.it is the best method to sace file.