Management of free space

• Free space file : Keep a file of free blocks on disk (for allocation)
• Bitmap : An array of bits (with an entry for each block). The bit corresponding to a block is set or cleared (depending on whether the block is empty or being used). The bitmap can be held in main store for efficiency - however, any system crash may cause inconsistencies between bitmap on disc and bitmap in main store

  
Figure 7: Bitmap