問63
頻出度★★☆
PC の補助記憶装置であるハードディスク装置の説明として, 適切なものはどれか。
平成24年度 春期 ITパスポート試験 問63
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 63
Incorrectア
The relative speeds are reversed. An HDD is generally faster to read and write than a CD-ROM drive; the CD-ROM drive is the slower of the two. Moreover, a CD-ROM is read-only, just as the name Read Only Memory indicates, so its write speed cannot be compared in the first place. This speed difference is one reason why the HDD is routinely used as the everyday secondary storage that holds the OS and files, while optical discs are used as media for distribution and storage.
Incorrectイ
This confuses the roles of main memory and secondary storage. Main memory is the storage that the CPU reads and writes directly, and semiconductor memory (DRAM) is used for it. The CPU cannot read or write an HDD by directly specifying addresses; the HDD is ultimately secondary storage, whose data must first be loaded into main memory before it is processed. There is, to be sure, a mechanism called virtual memory that makes part of an HDD look like a substitute for main memory when main memory runs short, but that is only the OS swapping data between main memory and the HDD — it does not make the HDD into main memory itself.
Incorrectウ
An HDD is non-volatile storage: even when the power is turned off, the data remains on the platters as the orientation of magnetization. That is exactly why files are still saved after the power has been shut down. Volatile storage, whose contents are lost when the power supply is cut off, is the DRAM and the like used for main memory, so this statement describes a property of main memory. Volatile versus non-volatile is a representative point of view for distinguishing main memory from secondary storage, so do not confuse the two.
- エ
正解 A hard disk drive (HDD) is a secondary storage device in which platters (magnetic disks) coated with a magnetic material spin at high speed while a magnetic head moves over them to read and write data. To reach the position to be read or written, the head is moved to the target track (a seek), and then the drive waits for the rotation to bring the target sector into place; through these steps any location can be accessed directly. In other words, there is no need to follow the data in order from the beginning — the drive can go straight to where the needed data is stored — so random access (direct access) is possible. It is precisely because of this property that an HDD is suited to holding the OS, applications, and large numbers of files that are read and written at any time. By contrast, a device such as magnetic tape, which can reach a target position only by advancing in order from the beginning, is limited to sequential access, and this is the decisive difference from an HDD. Therefore エ is appropriate.
ここがポイント
- Secondary storage devices use two access methods: random access (direct access), which can position directly at any location, and sequential access, which follows the data in order from the beginning. Disk-type devices such as HDDs, SSDs, and CD/DVDs are classified as random access, while magnetic tape is classified as sequential access.
- Grasp the difference between main memory and secondary storage. Main memory is read and written directly by the CPU; it is fast but volatile, and its capacity is small. Secondary storage cannot be read or written directly by the CPU; it is slow but non-volatile, and its capacity is large. The HDD belongs on the secondary storage side, and its typical characteristics are that it is non-volatile, has a large capacity, and is faster than a CD-ROM.
用語