問83
頻出度★★☆
PCに利用される DRAM の特徴に関する記述として, 適切なものはどれか。
平成21年度 秋期 ITパスポート試験 問83
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This question's explanation and your answers so far.
解説
問 83
Incorrectア
The speed relationship is the other way around. SRAM, which stores data with flip-flops, is faster, and DRAM, which needs refreshing, is slower than SRAM. That is exactly why SRAM is used for the CPU cache memory and DRAM for the main memory.
- イ
正解 イ is correct. DRAM (Dynamic RAM) stores one bit with one capacitor and one transistor, so the circuit per storage cell is simpler than in SRAM and many more bits fit into the same area. This gives it the characteristics of large capacity at low cost, which is why it is adopted as the main memory that a PC needs in large amounts. Its drawback is that the charge in the capacitor leaks away over time, so refreshing (rewriting) at fixed intervals is required, but for main memory the advantage in cost per capacity is the deciding factor.
Incorrectウ
DRAM is a volatile memory: once the power supply stops, the charge in the capacitors is lost and the stored contents disappear. Retaining contents after the power is turned off is a property of non-volatile memory such as ROM and flash memory (SSDs, USB flash drives, and the like).
Incorrectエ
DRAM is a kind of RAM, and both reading and writing can be done freely. What is read-only is ROM (Read Only Memory), a different category of memory from DRAM.
ここがポイント
- Comparison of DRAM and SRAM: DRAM uses capacitors, needs refreshing and is slower, but offers large capacity at low cost, so it is used as main memory. SRAM uses flip-flops and is fast but expensive and small in capacity, so it is used as cache memory.
- Distinguish two separate classification axes: volatile (RAM: contents vanish when power is lost) versus non-volatile (ROM, flash memory: retained even without power), and readable-and-writable (RAM) versus read-only (ROM).
用語