ITPEC FE Morning April 2020 Question 11

SRAM needs no refresh, DRAM does — SRAM holds each bit in a flip-flop, while DRAM holds it as charge in a capacitor that leaks away.

An SRAM cell is a flip-flop of about six transistors with two stable states, so it keeps its value as long as power is on. It is fast but large and expensive, and is used for cache memory. A DRAM cell is one transistor and one capacitor; the charge leaks, so every row must be refreshed at fixed intervals, but the cells pack densely and serve as main memory.

Answer (c)

Why not others:

• •(a) — reversed: an idle DRAM keeps spending power on refresh, while an idle SRAM only holds its flip-flop states, so SRAM has the lower standby consumption
• •(b) — reversed: SRAM needs about six transistors per bit against DRAM's one transistor and one capacitor, which is why DRAM is denser
• •(d) — swaps the two cell types: capacitors belong to DRAM and flip-flops to SRAM

Key rule: "Static" means flip-flop cells with no refresh (fast, used for cache); "dynamic" means capacitor cells that need refresh (dense, used for main memory).

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