Answer Description

Dual Data Rate (DDR) 3 Small Outline Dual Inline Memory Module (SO-DIMM) uses 204 pins. DDR and DDR2 pin counts can have 100, 144 or 200 pins. DDR4 SO-DIM uses 260 pins. SO-DIMM RAM is primarily used in laptops and other small devices.

Wikipedia

A SO-DIMM (pronounced "so-dimm" , also spelled "SODIMM") or small outline DIMM, is a type of computer memory built using integrated circuits. A SO-DIMM is a smaller alternative to a DIMM, being roughly half the physical size of a regular DIMM. SO-DIMMs are often used in systems that have limited space, which include laptops, notebooks, small-footprint personal computers such as those based on Nano-ITX motherboards, high-end upgradable office printers, and networking hardware such as routers and NAS devices. They are usually available with the same size data path and speed ratings of the regular DIMMs though normally with smaller capacities.