Learn in the textbookBasics of Semiconductor Memory — RAM, ROM, and Volatility
DefinitionRAM is semiconductor memory whose data can be freely read and written, used to hold programs and data temporarily while the computer processes them.
ExplanationThe storage that the CPU reads and writes directly is called main memory (主記憶), and RAM is used for it. RAM includes DRAM, which must be rewritten periodically (refresh, リフレッシュ) because its stored charge leaks away, and SRAM, which needs no refresh. A small, fast memory placed between the CPU and main memory to bridge their speed gap is called cache memory (キャッシュメモリ).
AnalogyIt is like the top of a work desk. You can freely add to the papers spread on it, but once you clear it at the end of the day (power off), nothing is left on the desk.
Memory hookRandom Access means that any address can be reached in about the same time; the name itself contains no word for "read" or "write".