問81
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フラッシュメモリに関する記述として, 適切なものはどれか。
平成22年度 春期 ITパスポート試験 問81
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 81
Incorrectア
A medium on which data can be written only once and that is read-only thereafter describes PROM (ROM that can be written only once) or write-once media such as CD-R and DVD-R. Flash memory can be erased electrically in units of blocks and rewritten any number of times, which is exactly why it can be used to store and delete data repeatedly, as with USB flash drives and SD memory cards. Be careful not to confuse the fact that the number of rewrites has an upper limit (a lifetime) with being writable only once.
- イ
正解 The correct answer is イ. Flash memory is a semiconductor memory in which data can be written electrically and erased in blocks all at once, and it is classified as a type of EEPROM (ROM that can be electrically erased and rewritten). Its greatest feature is that it is non-volatile: even when the power is turned off, the stored contents remain as they are, so no power has to be supplied continuously in order to retain them. It is precisely because of this property that it can be used in USB flash drives, SD memory cards, SSDs, and the built-in storage of smartphones and digital cameras, all of which are carried around with the power off. A useful contrast to remember is DRAM, which is used for main memory: DRAM is volatile memory, so even while it is powered it must be rewritten (refreshed) at fixed intervals to keep its charge, and its contents are lost when the power is turned off. The statement that no power supply is needed to retain the stored contents is the very definition of non-volatile memory, so イ is appropriate.
Incorrectウ
This is the exact opposite of the facts. Flash memory is a semiconductor memory with no moving parts, so it is easy to make small and thin, it is resistant to shock, and it consumes little power. That is why media the size of a postage stamp or a fingernail, such as SD memory cards and microSD cards, are possible, and flash memory is in fact the mainstream recording medium for digital cameras. What is hard to miniaturize and unsuited to portable devices is rather the magnetic disks and optical discs that need a mechanism to spin a platter.
Incorrectエ
It is optical discs such as CD, DVD, and Blu-ray Disc that read and write data by shining laser light on them. Flash memory uses no optical system at all; it reads, writes, and erases purely through electrical operations that move charge into and out of memory cells. Whether the recording method is electrical (flash memory), optical (CD / DVD), or magnetic (hard disk, magnetic tape) is a frequently tested classification, so it is worth organizing it medium by medium.
ここがポイント
- Flash memory is a non-volatile semiconductor memory that can be erased and rewritten electrically (a type of EEPROM). Its contents do not disappear when the power is turned off, so it is widely used in USB flash drives, SD memory cards, SSDs, recording media for digital cameras, and so on. There is an upper limit on the number of rewrites, but that does not mean it can be written only once.
- The distinction between non-volatile (contents retained when the power is off: ROM, flash memory) and volatile (contents lost when the power is off: RAM) is the core of this question. It is also worth organizing the contrast on the main-memory side, where DRAM needs refreshing and SRAM does not, as well as the classification of media by recording method: electrical (flash memory), optical (CD / DVD), or magnetic (hard disk).
用語