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CPU cache is built from SRAM. Why isn't all of a computer's memory SRAM?

SRAM takes 4 to 6 transistors per bit, so it is big and expensive.

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  1. SRAM loses data faster
  2. SRAM is slower than DRAM
  3. Each SRAM bit uses 4 to 6 transistors ✔

Why: SRAM is fast and needs no refresh, but each bit needs four to six transistors. A common DRAM cell uses one transistor and one capacitor, so DRAM packs far more bits into the same chip area.

Huh, didn't know that: Both SRAM and DRAM are volatile: cut the power and both forget everything.

The dad joke
Why is SRAM so expensive? It needs a whole team of transistors for every single bit.
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References

Answer: Each SRAM bit uses 4 to 6 transistors. SRAM is fast and needs no refresh, but each bit needs four to six transistors. A common DRAM cell uses one transistor and one capacitor, so DRAM packs far more bits into the same chip area.

  1. OpenStax Introduction to Computer Science 5.5: Memory Hierarchy openstax.org/books/introduction-computer-science/pages/5-5-memory-hierarchy
    SRAMs are bigger in area; a single bit requires a large area in the chip as it needs four to six transistors
    Checked 2026-10-10.

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