Hardware components of the PC Main Memory SIMM, DIMM and RIMM Main memory modules are available in different shapes and sizes and are illustrated below. SIMM, DIMM and RIMM describe the different production designs. These memory modules consist of memory chips mounted or hard-wired on a single PCB that connects to the system board via an edge connector. 72-pin SIMM (Single In-line Memory Module) The 72-pin SIMM has 72 individual connectors along its edge that makes contact with the system board. SIMMs have a 32-bit memory bus and transfer information to and from the CPU in 32-bit chunks. When installed with a Pentium processor that operates with a 64-bit memory bus, SIMMs work in pairs. 168-pin DIMM (Dual In-line Memory Module) The DIMM is a 168-pin version of the SIMM and more significantly have a 64-bit memory bus and transfer information to and from the CPU in 64-bit chunks. This design of RAM is used in single modules with Pentium processors. 184-pin RIMM (Rambus In-line Memory Module) Rambus RAM uses a dedicated high-speed bus to communicate with the CPU. The result is a faster overall performance from the computer.