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MOS memories — Identify which types of read/write semiconductor memories are available in mainstream MOS technology.

Difficulty: Easy

Correct Answer: both of the above

Explanation:


Introduction / Context:
The question probes whether common read/write semiconductor memories implemented in MOS (metal–oxide–semiconductor) technology include static RAM (SRAM), dynamic RAM (DRAM), or both. Understanding this classification helps learners distinguish volatile, high-speed cache memories from high-density main memories, while connecting each to its underlying device physics and circuit techniques.

Given Data / Assumptions:

  • We are considering standard MOS processes used for VLSI memory fabrication.
  • “Read/write memory” means the contents can be both read and rewritten during normal operation.
  • Focus is on volatile memories commonly paired with CPUs.


Concept / Approach:
SRAM stores each bit in a bistable MOS circuit (often a 6-transistor cell) that holds state as long as power is present, without refresh. DRAM stores each bit as charge on a tiny capacitor accessed through a MOS transistor, offering much higher density but requiring periodic refresh. Both are fabricated using MOS processes and support read and write operations at runtime, hence both qualify as MOS read/write memories.

Step-by-Step Solution:

Identify SRAM: MOS cross-coupled inverters (bistable), no refresh needed while powered, very fast access, lower density.Identify DRAM: MOS access transistor + capacitor, requires refresh, slower per access than SRAM but extremely dense and cost-effective.Determine scope: Both are MOS and both are read/write memories.


Verification / Alternative check:

Inspect processor memory hierarchies: on-chip caches (SRAM) and off-chip system memory (DRAM) are both MOS and both read/write.


Why Other Options Are Wrong:

SRAM: True but incomplete; DRAM also qualifies.DRAM: True but incomplete; SRAM also qualifies.none of the above: Incorrect; both are standard MOS read/write memories.


Common Pitfalls:

Equating “MOS” only with non-volatile types like EPROM/EEPROM/flash and forgetting volatile MOS RAMs.Assuming only one of SRAM or DRAM is MOS-based.


Final Answer:

both of the above
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