DIMM (Dual In-line Memory Module)

Notes

The name distinguishes it from the older single in-line SIMM, whose contacts were shorted across both faces.

Overview

A DIMM, short for dual in-line memory module, is a small circuit board carrying several DRAM chips that plugs into a slot on a computer's motherboard to provide its main memory. It is the form in which PC and server memory is bought, fitted and upgraded, so memory makers sell DRAM chips both on their own and assembled into modules. The name refers to the separate electrical contacts on each side of the edge connector, unlike the older SIMM, whose two sides were joined.

How it works

A DIMM puts a row of DRAM chips on one or both sides of a printed circuit board and routes them to gold contacts along its bottom edge. The memory controller in the processor reads and writes the whole module as one wide word, typically 64 data bits, or 72 bits on ECC modules that add a spare chip's worth of check bits so the system can correct single-bit errors. A notch in the edge connector, placed differently for each generation, stops a module from being fitted into the wrong slot.

DIMMs come in variants. Unbuffered DIMMs (UDIMMs) connect the controller straight to the chips and are the usual choice in desktop PCs. Registered DIMMs (RDIMMs) add a registering clock driver that buffers command, address and clock signals, so a server channel can carry more chips and more capacity. Shorter SO-DIMMs serve laptops and small systems.

With DDR5, more of the system moved onto the module. Server modules now carry a power management IC, an SPD hub that reports the module's configuration and temperature to the host, and extra temperature sensors. JEDEC standards set each module's pins, dimensions and electrical rules; a DDR5 UDIMM has 288 pins and a 1.1 V supply.

Examples

• A DDR4 desktop DIMM with eight DRAM chips on one side, bought to upgrade a PC from 16 GB to 32 GB.
• A DDR5 RDIMM in a data centre server, whose registering clock driver lets each channel support more memory.
• An ECC DIMM in a workstation, with extra chips holding check bits so that single-bit errors are corrected.
• A DDR5 module carrying its own power management IC and an SPD hub that reports temperature to the system over the I3C bus.

Why it matters

DIMMs are where most DRAM chips meet the market, and module choices decide how much memory a server can hold, how fast it runs and how reliably it stores data. Memory module designers, signal integrity engineers, server board designers and memory product and applications engineers all work on them.

In the chip lifecycle, the DIMM matters after the DRAM die is made: chips are tested and binned, mounted on modules with their buffer and power chips, tested again at module level, and validated in host systems before production; module standards also shape the requirements for the next DRAM generation.

It matters most to: Memory Applications Engineer, Memory Interface Signal Integrity Engineer, Memory Product Engineer, Memory Systems Architect, Server Board Hardware Engineer

Common confusions

Not the same as a DRAM chip

A DRAM chip is one packaged die. A DIMM is the board that carries many of them, together with buffer, power and configuration chips on newer modules.

Not the same as a memory channel

A channel is the bus from the processor's memory controller, and it may serve more than one DIMM slot. Adding DIMMs to a channel adds capacity, not bandwidth.

Not the same as a memory rank

A rank is a set of chips addressed together. One DIMM can hold one, two or more ranks, and a dual-sided module is not always dual-ranked.

Related standards

• JESD308 (DDR5 unbuffered DIMM common standard)

Sources

1. DDR5 Unbuffered Dual Inline Memory Module (UDIMM) Common Standard, JESD308 (opens in a new tab), JEDEC, 2026-10-22
2. DDR5 Server DIMM Chipset: Memory Interface Chips (opens in a new tab), Rambus, 2026-10-22
3. DIMM (Wikipedia) (opens in a new tab), Wikimedia Foundation, 2026-10-22

Related terms

• RDIMM
• UDIMM
• SODIMM
• Rank

Where it appears on the Hub

Used on 6 pages of the Hub. In each group, the pages that mention it most come first.