問52
頻出度★★☆
PCの処理効率を高めるために, CPUが主記憶にアクセスする時間を見かけ上短縮することを目的としたものはどれか。
平成27年度 春期 ITパスポート試験 問52
テクノロジ系コンピュータ構成要素 › メモリ
This question's explanation and your answers so far.
解説
問 52
Incorrectア
An SSD (Solid State Drive) is an auxiliary storage device that uses flash memory; as a replacement for an HDD it makes startup and file reading and writing faster. What becomes faster is access to auxiliary storage, not the access time between the CPU and main memory. The level asked about in the question (CPU to main memory) is different, so this is wrong.
Incorrectイ
Virtual memory is a technique that uses part of auxiliary storage in place of main memory, making it appear that there is a memory space larger than the actual main memory capacity. Its purpose is to apparently enlarge the capacity, not the speed. On the contrary, when paging (swapping) occurs, access to slow auxiliary storage takes place, so in terms of speed it works in the direction of making things slower.
- ウ
正解 The correct answer is ウ, cache memory. Main memory is slow compared with the operating speed of the CPU, so the CPU is kept waiting every time it goes to read main memory. Therefore a memory that is small in capacity but extremely fast is placed between the CPU and main memory, and it holds copies of frequently used data and instructions. This is cache memory. The next time the same data is needed, the CPU can read it from the cache without going all the way to main memory (a hit), so the waiting time is reduced. Main memory itself has not become faster, but the average access time as seen from the CPU becomes shorter, that is, it is apparently shortened. This matches exactly the purpose stated in the question, so ウ is the correct answer.
Incorrectエ
Defragmentation is a maintenance task that rearranges fragmented files on a hard disk into contiguous areas so as to improve the efficiency of disk reading and writing. Its target is auxiliary storage, and it has nothing to do with the time the CPU takes to access main memory, so it is wrong.
ここがポイント
- Cache memory is a small, high-speed memory placed between the CPU and main memory. It holds frequently used data and apparently shortens the average access time to main memory as seen from the CPU. In the memory hierarchy (registers > cache > main memory > auxiliary storage), the higher the level, the faster, the smaller in capacity, and the more expensive it is.
- Distinguishing confusing terms: virtual memory apparently enlarges capacity, while cache memory apparently increases speed. Both SSD and defragmentation are matters on the auxiliary storage side, not the speeding up of main memory access.
用語