A DIMM (dual in-line memory module) is a double SIMM (single in-line memory module). Like a SIMM, a DIMM is a module that contains one or several random access memory chips on a small circuit board with pins that connect it to the computer motherboard.
Dynamic random-access memory (DRAM) is a type of random access semiconductor memory that stores each bit of data in a separate tiny capacitor within an integrated circuit. The capacitor can either be charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1.
Static random access memory (SRAM) is a lot faster and does not require refreshing like dynamic RAM. While SRAM can operate at higher speeds than DRAM, it is more expensive to manufacture because of its complex internal structure, so most of the RAM on the motherboard is DRAM.