問69
頻出度★★☆
PCのプロセッサ内にあるキャッシュメモリの利用目的はどれか。
平成21年度 春期 ITパスポート試験 問69
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 69
Incorrectア
Retaining stored content even when the power is cut off is a characteristic of non-volatile memory (flash memory, SSD, ROM, and so on). Cache memory is volatile memory built from high-speed SRAM, and its content is lost once the power supply stops. It is a mechanism for gaining speed, not a mechanism for keeping data stored.
Incorrectイ
Recording information that does not need to be rewritten, or information that must not be rewritten, is the use of ROM (read-only memory); startup programs such as the BIOS are an example. The content of cache memory is only a temporary copy of data in main memory, and it is replaced one after another by new data (being rewritten is the premise), which is exactly the opposite.
- ウ
正解 The correct answer is ウ. Compared with the operating speed of the CPU, the access speed of main memory is slow, so a waiting time occurs every time the CPU fetches data from main memory. To deal with this, a cache memory that is small in capacity but very fast is placed inside the processor, and data that has been read once or that is used frequently is copied into it. The next time the same data is needed, the CPU can read it from the nearby cache instead of the slow main memory (a cache hit), so the waiting time is reduced. Main memory itself has not become faster, but from the CPU's point of view the access time to main memory appears to have been shortened. This apparent shortening reduces the time the CPU is kept waiting and raises processing efficiency. That is the purpose of cache memory.
Incorrectエ
Safely recording important or confidential information such as user IDs and passwords is the role of tamper-resistant devices such as a security chip (TPM) or an IC card. Cache memory is a storage device for making processing faster; it is not a component whose purpose is to protect information (to maintain confidentiality).
ここがポイント
- Cache memory = a small-capacity, high-speed memory placed inside the processor to fill the speed gap between the CPU and main memory. By keeping copies of frequently used data close at hand, it apparently shortens the access time to main memory and raises the CPU's processing efficiency.
- Remember storage devices by distinguishing mechanisms meant for speed from mechanisms meant for storing and protecting. Cache memory is for speed (volatile), flash memory and ROM are for storage that survives power-off, and TPM and IC cards aim at protecting confidential information.
用語