SO-DIMM

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PC2700 200-pin DDR 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, or 200 pins. The 100 pin package supports 32-bit data transfer, while the 144 and 200 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 variations for locating the notch which are nearly indistinguishable to the naked eye. If the notch is located further outboard (19 contacts between the notch and the edge of the board), it indicates the DDR2 class of memory. When the notch is located nearer the center of the board (20 contacts between the notch and the edge of the board), it indicates DDR. These two types of memory are not interchangeable, and the different notch locations prevent incorrect installation. The PC5300 200-pin SO-DIMM depicted in the accompanying photograph has the notch slightly outboard, and is thus DDR2. 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 400Mhz 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 and 1066 MHz PC2-8500 are becoming available.