Chapter 11.2: File System Implementation Chapter 11: File System Implementation Chapter 11.1 File-System Structure File-System Implementation Directory Implementation Allocation Methods Chapter 11.2 Free-Space Management Recovery Log-Structured File Systems
0 block[i] free
1 block[i] occupied
A sample bit vector might appear as 0011110011111100110011 ….
This is a very simple approach but very efficient in finding the first free block.
Too, a number of instruction sets contain instructions for bit manipulation
We can see also how hardware features drives software functionality.
Downside: to be efficient in searching, the bit map must be kept in primary memory.
For small disks, there is not a problem, but for larger disks (say a 40GB disk with 1KB blocks) a bit map of 5MB is needed!!
Shows that address of first free block
points to the disk area, where other
blocks are linked from one to the next.