A narrow printed circuit board that holds memory chips (RAM chips). The common architecture for desktop computers is the dual in-line memory module (DIMM). Because of space limitations, laptops use small outline DIMMs (SODIMMs). The modules have notches in different places so that they cannot be inserted into the wrong slots (see illustration below). Error Detection and Correction Many computers use 8-bit RAM chips, while others use 9-bit chips. The ninth bit is a parity bit for detecting errors. High-end servers and workstations may use error-correcting memory (ECC) and registered DIMMs (RDIMMs). See ECC memory and RDIMM. Upgrading Memory - Read the Manual (RTFM!) A single DIMM can often be used, but pairs of DIMMs increase performance in machines that support dual channel DDR SDRAM. When upgrading memory, read the motherboard manual to find out which module combinations can be used. See SDRAM, memory types, memory card and Hybrid Memory Cube.