SO-DIMMs (also written SODIMMs) 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 PCs (such as those with a Mini-ITX motherboard), high-end upgradable office printers, and networking hardware like routers.
Visual identification 
Most types of SO-DIMMs can be recognized at a glance by the distinctive notches that “key” them for different applications:
- 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.
Variants of 200-pin SO-DIMMs 
The 200-pin SO-DIMM notch is in one of three locations:
- If the notch is located away from the center, it indicates the DDR class of memory.
- When the notch is located slightly closer to the center of the board, it generally (but not always) indicates that the RAM is of the DDR2 type.
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. DDR1 SO-DIMMs operate at 2.6 Volts while DDR2 SO-DIMMs operate at 1.8 Volts.
General characteristics 
200- and 204-pin SO-DIMMs measure at 6.76 cm in length and a width of 3.175 cm with a maximum total depth of 0.38 cm.
SO-DIMMs are more or less equal in power and voltage rating to DIMMs, and as memory technology moves forward and despite their smaller size, SO-DIMM technology allows for performance speeds as high as the those of the larger DIMMs[clarification needed] (clock speeds such as 400 MHz PC-3200, for example, and CAS latency such as 2.0, 2.5, and 3.0) and capacity (512MB, 1GB, etc.).
The latest 204-pin SO-DIMMs can contain DDR3 SDRAM, with specifications such as PC3-6400, PC3-8500, PC3-10600, and PC3-12800.
See also 
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