Fragentation(external) can occur.
   As task finishes, segments freed.

   However, if new task needs larger segment than freed one

   Another segment allocated.

   Eventually, all of memory fragmented in block too small to use.

   Requiring segment consolidation or "garbage collection" 

   Its possible to combine paging and segmentation.
    Usually memory is segmented.

   Then each segment is divided up into pages 
     and each segment given its own page table.