Re: DIMM vs SO-DIMM
Your laptop takes only DDR3 SO-DIMM which is 204-pins. 240-pin memory is the desktop version, and only for desktops.
DIMM again is only for desktops.
Having two sticks of the same or similar memory will take advantage of having them run in dual channel mode which will increase the memory bandwidth and performance. Running one single stick will run in single channel.
3770K | ASUS STRIX GTX 1080 | DDR3-1600 16GB | CORSAIR 650D | CORSAIR HX 850W | CORSAIR H100 | SOUND BLASTER Z | ASROCK EXTREME4 GEN3