File system checkers often take advantage of the block status map used to identify unallocated disk blocks. The basic idea is for the map to be copied into the checker’s address space, with each entry in the map enlarged to capture more possibilities for the block’s state (for example, allocated, not allocated, duplicate allocation, already checked, etc.). Devise an algorithm to use the block status table to check a disk to see if every block on the disk appears in one, and only one, file or on the free list.