DIMM

It is a printed circuit board with one or both sides (front and back) holding DRAM chips and pins.

[6] The name "DIMM" was chosen as an acronym for Dual In-line Memory Module symbolizing the split in the contacts of a SIMM into two independent rows.

[13] They are usually available with the same size data path and speed ratings of the regular DIMMs though normally with smaller capacities.

A DIMM's capacity and other operational parameters may be identified with serial presence detect (SPD), an additional chip which contains information about the module type and timing for the memory controller to be configured correctly.

[14] ECC DIMMs are those that have extra data bits which can be used by the system memory controller to detect and correct errors.

DIMMs are often referred to as "single-sided" or "double-sided" to describe whether the DRAM chips are located on one or both sides of the module's printed circuit board (PCB).

However, these terms may cause confusion, as the physical layout of the chips does not necessarily relate to how they are logically organized or accessed.

JEDEC decided that the terms "dual-sided", "double-sided", or "dual-banked" were not correct when applied to registered DIMMs (RDIMMs).

For various technologies, there are certain bus and device clock frequencies that are standardized; there is also a decided nomenclature for each of these speeds for each type.

To alleviate this issue, the next standards of DDR DIMMs were created with a "low profile" (LP) height of around 1.2 inches (30 mm).

With the advent of blade servers, angled slots have once again become common in order to accommodate LP form factor DIMMs in these space-constrained boxes.

This led to the development of the Very Low Profile (VLP) form factor DIMM with a height of around 0.72 inches (18 mm).

[17] As of Q2 2017, Asus has had a PCI-E based "DIMM.2", which has a similar socket to DDR3 DIMMs and is used to put in a module to connect up to two M.2 NVMe solid-state drives.

Two types of DIMMs: a 168-pin SDRAM module (top) and a 184-pin DDR SDRAM module (bottom). The SDRAM module has two notches (rectangular cuts or incisions) on the bottom edge, while the DDR1 SDRAM module has one. Also, each module has eight RAM chips, but the lower one has an unoccupied space for the ninth chip; this space is occupied in ECC DIMMs.
Three SDRAM DIMM slots on a ABIT BP6 computer motherboard.
72-pin SO-DIMM
256 MB MicroDIMM PC133 SDRAM (double sided, 4 chips).
Assorted SO-DIMM Modules
A 200-pin PC2-5300 DDR2 SO-DIMM.
A 204-pin PC3-10600 DDR3 SO-DIMM.
A SO-DIMM slot on a computer motherboard .
Notch positions on DDR (top) and DDR2 (bottom) DIMM modules.
16 GiB DDR4-2666 1.2 V Unbuffered DIMM (UDIMM) .
A comparison between 200-pin DDR and DDR2 SDRAM SO-DIMMs, and a 204-pin DDR3 SO-DIMM module. [ 15 ]