Dynamic RAM (DRAM) refresh timing – typical interval Typically, how often must a DRAM array be refreshed to preserve stored data (order-of-milliseconds range)?

Introduction / Context:
DRAM cells store data as charge on tiny capacitors, which leak over time. Refresh cycles periodically read and rewrite each row to restore charge. Understanding the order of magnitude of refresh intervals is fundamental to memory controller design.

Given Data / Assumptions:

• Conventional single-data-rate and early-generation DRAMs.
• Refresh specified over all rows within a few milliseconds.
• Exact timing varies by generation and temperature, but typical teaching values are a few milliseconds.

Concept / Approach:
Manufacturers specify a maximum interval within which all rows must be refreshed (for example, every 2–8 ms or 4–16 ms historically). The key concept is that refresh is millisecond-scale, not microseconds per full array (though row refreshes themselves occur in microseconds or less).

Step-by-Step Solution:
Identify the correct scale: millisecond range for the entire array, not microseconds.Select the common textbook interval: 2 to 8 ms fits typical legacy specifications.Therefore, choose 2 to 8 ms as a representative “typical” value.

Verification / Alternative check:
Older DRAM standards often specified full-array refresh on the order of a few milliseconds; later devices may use 64 ms at normal temperature, but many basic electronics texts use 2–8 ms as the canonical range for examples.

Why Other Options Are Wrong:
4 to 16 ms is plausible historically, but the more commonly cited “typical” in many entry texts is 2–8 ms.Microsecond options (8–16 µs, 1–2 µs) are far too short for full-array intervals.Hundreds of milliseconds would allow excessive leakage and data loss.

Common Pitfalls:
Confusing per-row refresh timing with full-array interval; not accounting for temperature-dependent refresh needs.

Final Answer:
2 to 8 ms