What is external fragmentation?

As process are removed from and loaded to the memory free memory space is bracken into pieces .external fragmentation take place when enough memory space exists to satisfy a request, however it isn't contagious, storage is fragmented in to large number of small holes.

• External fragmentation: leftover holes are excessively small to hold a new program even though there may be enough total free memory to do so.
• Bookkeeping for holes is able to be expensive a 1 byte hole requires an entire record in the table.
• To decrease on space overhead, the memory is allocated in fixed-size blocks.