問59
頻出度★☆☆
仮想記憶を利用したコンピュータで, 主記憶と補助記憶の間で内容の入替えが頻繁に行われていることが原因で処理性能が低下していることが分かった。この処理性能が低下している原因を除去する対策として, 最も適切なものはどれか。ここで, このコンピュータの補助記憶装置は1台だけである。
令和2年度 ITパスポート試験 問59
テクノロジ系ソフトウェア › オペレーティングシステム
This question's explanation and your answers so far.
解説
問 59
Incorrectア
Even if you raise the CPU's processing power, the bottleneck—frequent swapping caused by insufficient main memory—is not resolved. Rather, the CPU merely sits idle waiting for swaps (I/O), so it does not eliminate the cause of the performance degradation.
Incorrectイ
If you increase the virtual memory capacity, the range that auxiliary storage takes over for what does not fit in main memory expands, which may instead increase swapping and make things worse. The cause—insufficient real memory—is not resolved.
- ウ
正解 The phenomenon where performance degrades because content is frequently swapped (page-in/page-out) between main memory and auxiliary storage is called “thrashing.” Its cause is that the main memory capacity is insufficient relative to the amount of data required to run the programs. If you increase the capacity of the main memory unit, more pages can be kept in main memory, and the number of swaps with auxiliary storage itself decreases. Therefore, “ウ” is the most appropriate measure to eliminate the root cause of the performance degradation.
Incorrectエ
Even if you replace the auxiliary storage with a larger-capacity device, the fact that swapping occurs frequently does not itself change. Since the cause is insufficient main memory rather than capacity, it does not eliminate the cause of the performance degradation.
ここがポイント
- Thrashing = a phenomenon where, due to insufficient main memory, page swaps (page-in/page-out) occur frequently and performance drops sharply. The first countermeasure is to add more main (real) memory.
- With virtual memory, increasing the “virtual memory capacity” does not resolve a shortage of real memory. The key point is to identify where the bottleneck actually lies (real memory).
用語