External fragmentation is much more difficult to quantify than internal frag- mentation because it depends not only on the pattern of previous requests and the allocator implementation, but also on the pattern of future requests.

For example, suppose that after k requests all of the free blocks are exactly four words in size. Does this heap suffer from external fragmentation?

The answer depends on the pattern of future requests.

If all of the future allocate requests are for blocks that are smaller than or equal to four words, then there is no external fragmentation. On the other hand, if one or more requests ask for blocks larger than four words, then the heap does suffer from external fragmentation.