Which of the following computer memory types are volatile? (A) CMOS memory (B)…

Memory is classified as volatile if it requires continuous electrical power to retain its stored data — cut the power and the data is lost — and non-volatile if it retains data even when power is removed, whether because the storage technology itself does not need power, or because it is kept continuously powered by a dedicated backup source.

Applying this to the five memory types in the question:

• CMOS memory (A) — built from SRAM cells, but on every PC/laptop it is wired to a small dedicated CMOS battery that keeps it powered at all times, even when the machine is off; because it never actually loses power, standard computer-architecture references and exam conventions classify it as non-volatile (similar to battery-backed NVRAM).

• Cache memory (B) — high-speed SRAM built directly into or near the CPU with no independent backup power; it loses its contents the instant system power is cut, so it is volatile.

• Flash memory (C) — uses floating-gate transistors that trap charge without any continuous power supply, so it retains data with the power fully off; it is non-volatile.

• Hard disk (D) — stores data as magnetic orientation on a platter, a physical state that persists with no power at all; it is non-volatile.

• RAM (E) — dynamic RAM cells must be continuously refreshed with power to hold a charge; remove power and the data is gone within moments, so it is volatile.

So among the five, only Cache memory (B) and RAM (E) meet the definition of volatile memory — they are the two types that lose their data the instant power is removed. CMOS memory is often mistaken for volatile because its SRAM cell technically needs power, but because that power is continuously supplied by the CMOS battery rather than the main system supply, it behaves as non-volatile storage in practice and in standard exam keys, matching option (B) and (E) only.