Counting

• Another approach is to take advantage of the fact that, generally, several contiguous blocks may be allocated or freed simultaneously, particularly when space is allocated with the contiguous-allocation algorithm or through clustering.
• Thus, rather than keeping a list of $n$ free disk addresses, we can keep the address of the first free block and the number $n$ of free contiguous blocks that follow the first block.
• Each entry in the free-space list then consists of a disk address and a count.
• Although each entry requires more space than would a simple disk address, the overall list will be shorter, as long as the count is generally greater than 1.