doubt

Question

Explain Internal And External fragmentation clearly??

Answer 1

Internal fragmentation is the wasted space within each allocated block
because of rounding up from the actual requested allocation to the
allocation granularity.  External fragmentation is the various free
spaced holes that are generated in either your memory or disk space.
External fragmented blocks are available for allocation, but may be
too small to be of any use.

Comments

then which type of fragmentation exist in fixed and variable size of memory??

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internal fragmentation exist in fixed and external fragmentation exist variable partitioning of memory
http://www.enggpedia.com/computer-engineering-encyclopedia/dictionary/299-operating-systems/1902-internal-external-fragmentation-differences?tmpl=component