Short for dual in-line memory module, a small circuit board that holds memory chips . A single in-line memory module (SIMM) has a 32-bit path to the memory chips whereas a DIMM has 64-bit path. Because the Pentium processor requires a 64-bit path to memory, you need to install SIMMs two at a time. With DIMMs, you can install memory one DIMM at a time. However, DIMMs are currently more than twice as expensive as SIMMs.