2GB Kit (1GB x 2) DDR2-PC6400 CL=5 UNBUFFERED NON-ECC DDR2-800 1.8V 128Meg x 64 240-pin DIMM...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 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 to each other. 240-pin DIMMs are used to provide DDR2 SDRAM memory for desktop computers. DDR2 is a leading-edge generation of memory with an improved architecture that allows it to transmit data very fast. Each 240-pin DIMM provides a 64-bit data path (72-bit for ECC or registered or Fully Buffered modules). (The Ballistix and Ballistix Tracer high-performance memory do not come in 72-bit or registered modules.) To use DDR2 memory your system motherboard must have 240-pin DIMM slots and a DDR2-enabled chipset. A DDR2 SDRAM DIMM will not fit into a standard SDRAM DIMM socket or a DDR DIMM socket. The number of black components on a 240-pin DIMM can vary but it always has 120 pins on the front and 120 pins on the back for a total of 240. 240-pin DIMMs are approximately 5.25 inches long and 1.18 inches high though the heights can vary. While 240-pin DDR2 DIMMs 184-pin DDR DIMMs and 168-pin DIMMs are approximately the same size 240-pin DIMMs and 184-pin DIMMs have only one notch within the row of pins. The notch in a 240-pin DDR2 DIMM is closer toward the center of the module.