SO-DIMM

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PC6400 DDR2 SO-DIMM

A SO-DIMM, 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 which have space restrictions such as notebooks, small footprint PCs (such as those with a Mini-ITX motherboard), high-end upgradable office printers, and networking hardware like routers.

SO-DIMMs have 72, 100, 144, 200 or 204 pins. The 72 and 100 pin packages supports 32-bit data transfer, while the 144, 200 and 204 pin packages support 64-bit data transfer. This compares to regular DIMMs that have 168, 184, or 240 pins, all supporting 64-bit data transfer.

Most types of SO-DIMMs can be recognized at a glance by the distinctive notches used to "key" them for different applications: 100-pin SO-DIMMs have two notches, 144-pin SO-DIMMs have a single notch near (but not at) the center, and 200-pin SO-DIMMs have a single notch nearer to one side.

The 200-pin SO-DIMM has two notch locations. If the notch is located away from the centre, it indicates the DDR class of memory. When the notch is located nearer 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 incorrect installation. Caution should be exercised when visually identifying 200-pin SO-DIMM modules.

SO-DIMMs are more or less equal in power and voltage rating to DIMMs, and as memory technology moves forward, both SO-DIMMs and DIMMs become available in equal speed (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.).

At the time of writing (May 2008) DDR2 SO-DIMM memory modules commonly have clock speeds from 200 MHz up to 800 MHz PC2-6400. Contrary to some claims 1066 MHz PC2-8500 do not exist.

There are also new 204-pin SO-DIMM memory modules with PC3-6400/PC3-8500/PC3-10600/PC3-12800 specifications.