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Fixed vs variable partitioning
Short answer
Fixed partitioning uses static partition sizes, causing internal fragmentation and simple management. Variable partitioning allocates partitions exactly as needed, avoiding internal fragmentation but creating external holes that require coalescing and compaction, achieving higher memory utilization with more overhead.
Prepare a comparative note on the fixed and variable partitioning multiprogramming techniques for real memory management.
Both are contiguous real-memory management schemes for multiprogramming: main memory is divided into partitions, each holding one process.
Fixed (static) partitioning divides memory into a fixed number of partitions of equal or unequal size at system start-up. Variable (dynamic) partitioning creates a partition of exactly the required size when a process is loaded; the partitions and their number change over time.
| Point | Fixed partitioning | Variable partitioning |
|---|---|---|
| Partition size | Fixed before execution | Created as per process size |
| Number of partitions | Fixed, so limits degree of multiprogramming | Variable |
| Internal fragmentation | Yes (partition larger than process) | None |
| External fragmentation | Not significant (but unusable free partitions exist) | Yes, holes appear as processes leave |
| Memory utilization | Low | Higher |
| Process size limit | Cannot exceed largest partition | Limited only by free memory |
| Allocation | Simple; queue per partition or a single queue | Needs first/best/worst fit algorithms |
| Management overhead | Low (simple table) | Higher (free-list, coalescing, compaction) |
| Relocation | Static, simpler | Needs dynamic relocation for compaction |
| Example | IBM OS/360 MFT | IBM OS/360 MVT |
Example: memory 100 K, processes of 30 K, 25 K, 20 K. With fixed 25 K partitions the 30 K process cannot be loaded and the 20 K process wastes 5 K. With variable partitioning all three fit exactly (75 K used, 25 K hole).
In short, fixed partitioning is simple but wasteful; variable partitioning uses memory efficiently but suffers external fragmentation, which requires coalescing and compaction.
✓ Answer checked by Claude Opus 5.5 (high effort)
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