ITPEC FE Morning October 2022 Question 22

SRAM — static RAM stores each bit in a flip-flop, so a cell holds its value without refresh for as long as power is on.

An SRAM cell is a flip-flop built from 4 to 6 transistors: two cross-coupled inverters with two stable states, one for 0 and one for 1. The state persists without any refresh, which makes SRAM fast, but each cell is large and expensive, so it is used for cache memory. A DRAM cell is one transistor and one capacitor; the charge leaks away, so it must be refreshed periodically, but it packs densely and serves as main memory.

Answer (d)

Why not others:

• •(a) DRAM — stores a bit as charge in a capacitor and needs periodic refresh
• •(b) EEPROM — stores a bit as charge trapped in a floating-gate transistor; it is non-volatile and electrically erasable, with no flip-flop
• •(c) SDRAM — DRAM that runs synchronised with the bus clock; the S means synchronous, and its cells are still capacitors

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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