DRAM (Dynamic RAM)

DRAM (dynamic random-access memory) is a type of volatile memory that stores each bit as an electrical charge in a tiny capacitor paired with a transistor. Because the charge leaks away, every cell must be refreshed many times per second. Modules such as DDR4 and DDR5 are DRAM.

Why it matters

DRAM is the system's main working memory. It is far faster than flash storage and much cheaper than the SRAM used in CPU caches, which is why it sits in the middle of the memory hierarchy. When power is lost, everything in DRAM disappears.

Refresh is the cost of the simple one-capacitor design. A typical rule is that every row is refreshed about every 64 milliseconds, during which that part of the memory briefly cannot be accessed. Latency, measured in timings like CL, and bandwidth, set by data rate and channel count, determine real performance.

Example

A laptop with 16 GB of DRAM holds the operating system, open browser tabs, and running apps. If it runs out, the system swaps data to the SSD, which is far slower, and the machine feels sluggish.

Common mistakes

• Confusing DRAM with storage. Memory loses its contents at power-off.
• Mixing mismatched modules and losing dual-channel performance.
• Assuming SRAM and DRAM are interchangeable; SRAM is faster and costs far more per bit.

Related

• RAM
• DDR5
• Cache memory
• ECC memory

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