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SESK: Stuff Everyone Should Know · sesk.info/tech-dram-refresh

Why does DRAM, the main memory in a computer, need to be refreshed every few milliseconds?

Its tiny capacitors leak charge, so the bits fade unless topped up.

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  1. To clear out old programs
  2. To cool the memory chips
  3. Its capacitors slowly lose their charge ✔

Why: DRAM stores each bit as charge on a tiny capacitor. The charge leaks away, so built-in circuits recharge every cell every few milliseconds. That constant refresh is the dynamic in dynamic RAM.

Huh, didn't know that: Each DRAM bit needs just one capacitor plus a transistor, which is why DRAM is much denser and cheaper than SRAM.

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Why did the DRAM need a nap every few milliseconds? It kept losing its charge.
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References

Answer: Its capacitors slowly lose their charge. DRAM stores each bit as charge on a tiny capacitor. The charge leaks away, so built-in circuits recharge every cell every few milliseconds. That constant refresh is the dynamic in dynamic RAM.

  1. OpenStax Introduction to Computer Science 5.5: Memory Hierarchy openstax.org/books/introduction-computer-science/pages/5-5-memory-hierarchy
    there is circuitry built inside the DRAM that, every few milliseconds, checks the capacitors and adds a charge to them
    Checked 2026-10-10.

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Tech & GadgetsCPU cache is built from SRAM. Why isn't all of a computer's memory SRAM?Tech & GadgetsOn a cache miss, how much data does a typical modern CPU cache pull in from memory?Tech & GadgetsWhich of these loses its contents when the computer loses power?

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