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, SODIMM, or small outline dual in-line memory module, is a type of computer memory built using integrated circuits SO-DIMMs are a smaller alternative to a DIMM, being roughly half the size of regular DIMMs SO-DIMMs are often used in systems that have limited space, which include laptops, notebooks, small-footprint personal computers such as those based on Mini-ITX motherboards, high-end upgradable office printers, and networking hardware such as routers and NAS devices
SO-DIMM - Wikipedia, the free encyclopedia