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A 200-pin PC6400 DDR2 SO-DIMM
A 204-pin PC3-10600 DDR3 SO-DIMM
A comparison between 200-pin DDR and DDR2 SDRAM SO-DIMMs, and a 204-pin DDR3 DIMM module
A SO-DIMM slot on a computer motherboard

An SO-DIMM, SODIMM, or small outline dual in-line memory module, is a type of computer memory built using integrated circuits.

SO-DIMMs are a smaller alternative to a DIMM, being roughly half the size of regular DIMMs. SO-DIMMs are often used in systems that have limited space, such as notebooks, small-footprint personal computers (such as those with a Mini-ITX motherboard), high-end upgradable office printers, and networking hardware like routers and NAS devices.[1]

Visual identification[edit]

Most types of SO-DIMMs can be recognized at a glance by the distinctive notches that “key” them for different applications:[citation needed]

  • 100-pin SO-DIMMs have two notches
  • 144-pin SO-DIMMs have a single notch near the center
  • 200-pin SO-DIMMs have a single notch nearer to one side. The exact location of this notch varies (read below.)
  • 204-pin SO-DIMMs (DDR3) have a single notch closer to the center than on 200-pin SO-DIMMs.
  • 260-pin SO-DIMMs (DDR4), 69.6 mm (2.74 inches) wide and 30 mm (1.2 inches) high, making them 2 mm (0.079 inches) wider than DDR3 SO-DIMMs, with a notch after pin 144.[2]
  • 260-pin SO-DIMMs (UniDIMM), 69.6 mm (2.74 inches) wide and 30 mm (1.2 inches) or 20 mm (0.79 inches) high, with the notch placed differently than on DDR3 SO-DIMMs.

Variants of 200-pin SO-DIMMs[edit]

The 200-pin SO-DIMM can be of the types DDR and DDR2. In both cases the notch is located at one fifth of the board length (20 pins + notch + 80 pins), but in DDR2 the notch is located slightly closer to the center of the board. These two types of memory are not interchangeable. The different notch locations are designed to prevent cross-installation. Keep this in mind when attempting to visually identify 200-pin SO-DIMM modules.

This variance is designed to prevent coupling of memory and controllers of different DDR generations due to electrical incompatibility. DDR SO-DIMMs operate at 2.5 Volts while DDR2 SO-DIMMs operate at 1.8 Volts.

General characteristics[edit]

200- and 204-pin SO-DIMMs are 67.6 mm (2.66 inches) long and 31.75 mm (1.250 inches) wide, with a maximum total depth of 3.8 mm (0.15 inches).[3]

SO-DIMMs are more or less equal in power and voltage rating to DIMMs, and despite the smaller size of memory modules, SO-DIMM technology does not mandate lower performance compared to larger DIMMs. For example, SO-DIMMs provide clock speeds such as 400 MHz (PC-3200), CAS latencies such as 2, 2.5 and 3, and higher capacities such as 512 MB or 1 GB.

DDR2 SO-DIMM memory modules commonly have clock speeds from 200 MHz up to 400 MHz (PC2-6400).[citation needed] 204-pin SO-DIMMs can also contain DDR3 SDRAM, with specifications such as PC3-6400, PC3-8500, PC3-10600, and PC3-12800.[4] 260-pin UniDIMMs may contain either DDR3 or DDR4 SDRAM, depending on their configuration. Some SO-DIMMs also provide ECC functionality; unbuffered ECC SO-DIMMs are called SO-CDIMMs.[5]

LowHal SODIMMs are made using a low-halogen, environmentally-friendly process,[6] which does not affect chip performance.

See also[edit]


  1. ^ Synology Inc. "Synology RAM Module". 
  2. ^ "DDR4 SDRAM SO-DIMM (MTA18ASF1G72HZ, 8GB) Datasheet" (PDF). Micron Technology. 2014-09-10. Retrieved 2014-11-20. 
  3. ^ - 200 Pin, PC2700 DDR SDRAM Unbuffered SO–DIMM REFERENCE DESIGN SPECIFICATION page 26
  4. ^
  5. ^ "Define-SO-CDIMM". RAMpedia. Retrieved 2014-08-24. 
  6. ^ "Low-Halogen RAM? - Lenovo Community". 2009-10-17. Retrieved 2014-08-24. 

External links[edit]