Source : Free On-Line Dictionary of Computing

Small Outline DIMM
     
         (SO-DIMM) A smaller kind of {DIMM} with 72 pins
        (supporting 32-bit transfers) or 144 pins (64-bit transfers).
        Regular DIMMs have 168 pins and support 64-bit transfers.
        Being roughly half the size of the regular DIMM, SO-DIMMs are
        often used in {notebook computers}.
     
        {Kingston Memory Guide
        (http://www.kingston.com/tools/umg/newumg05a.asp)}.
     
        (2001-02-16)