A dual inline memory module (DIMM) consists of a number of memory components (usually black) that are attached to a printed circuit board (usually green). The gold or tin pins on the bottom of the DIMM provide a connection between the module and a socket on a larger printed circuit board. The pins on the front and back of a DIMM are not connected, providing two lines of communication paths between the module and the system. 168-pin DIMMs are commonly found in Pentium and Athlon systems. Each 168-pin DIMM provides a 64-bit data path, so they are installed singly in 64-bit systems. 168-pin DIMMs are available in FPM, EDO, 66MHz SDRAM, PC100 SDRAM, and PC133 SDRAM. When upgrading, be sure to match the memory technology that is already in your system. (Information on which memory technology is used by your system is included in the Memory Selector.) The number of black components on a 168-pin DIMM may vary, but they always have 84 pins on the front and 84 pins on the back for a total of 168. 168-pin DIMMs are approximately 5.375" long and 1.375" high, though the heights may vary. They have two small notches within the row of pins along the bottom of the module.