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 fully buffered DIMMs (FBDIMMs) are used to provide DDR2 SDRAM memory for servers and motherboards that use FBDIMM technology, as opposed to conventional registered DIMM (RDIMM) technology. DDR2 is a leading-edge generation of memory with an improved architecture that allows it to transmit data very fast. FBDIMM technology utilizes an advanced memory buffer that allows modules to be connected in series — meaning that more memory modules can be connected (and thus memory density is increased) and errors at the connection points are reduced.

Each 240-pin DIMM provides a 64-bit data path (72-bit for ECC or registered or fully buffered modules).

DDR2 240-pin fully buffered DIMMs are available in DDR2 PC2-4200 SDRAM and DDR2 PC2-5300 SDRAM.

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.

To use fully buffered DIMMs, your server or motherboard must use FBDIMM architecture. An FBDIMM will not fit into a standard DDR2 socket, and a DDR2 module will not fit into an FBDIMM 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 fully buffered DDR2 DIMM is in a different location than the notch for regular 240-pin DDR2 modules.