Internal VS External Frag + Solve using Paging

Aspect	Internal Fragmentation	External Fragmentation
Definition	Wasted space inside an allocated fixed‐size block when the process doesn’t fill it completely.	Wasted space between allocated blocks: free memory breaks into small non-contiguous holes.
Cause	Rounding up a process’s memory request to the next whole partition/page size.	Dynamic allocate/deallocate of variable-sized chunks leaves scattered holes over time.
Location of Waste	Within the boundaries of an allocated page or fixed partition.	Between allocated regions in the free memory pool.
Example	A process needs 18 KB on a system with 4 KB pages ⇒ it gets 5 pages (20 KB), leaving 2 KB unused in the last page.	After freeing blocks of 100 KB, 150 KB, and 400 KB, a 350 KB request fails—no single hole ≥ 350 KB even though total free = 650 KB.
Occurs In	Fixed‐size schemes (paging, MFT).	Variable‐size schemes (MVT, segmentation).
Mitigation	Reduce block/page size; use variable‐sized allocation (segmentation/MVT).	Compaction (costly); paging—allow noncontiguous allocation of fixed‐size frames.

Eliminates External Fragmentation
- Physical memory is divided into equal‐sized frames and logical into pages.
- A process’s pages can occupy any free frames, so there’s no need for one large contiguous hole .
Limits Internal Fragmentation
- Some unused space remains in the last page of each process, but by choosing a small page size this waste is kept minimal (“Smaller page size → less internal fragmentation”) .
- Maximum per‐process waste = one page.
Simplifies Allocation & Sharing
- The OS keeps a free‐frame list and satisfies page‐faults by grabbing any free frame.
- Pages of different processes can share frames (read-only code), improving utilization.
Trade-Off
- Overhead: extra page-table storage and (without a TLB) two memory accesses per reference.
- But the dramatic reduction of external fragmentation and controlled internal fragmentation make paging the standard solution in modern OS memory management.