Original post by: Dan ,
The problems most people have is not using the correct RAM. Unlike a Windows system which allows you to dicker with the BIOS settings, Mac’s don’t have these tweaks available. So you really don’t want to use too high a spec’ed RAM SODIMM or of course use too slow as well. You need 1867 MHz PC3-14900 DDR3 SDRAM SO-DIMMs (204-pin) Buy from a name brand web site or large store like MicroCenter or BestBuy or even iFIXIT so you don’t get seconds or fake units and have a company that will support their product. As far as which slots to use if you are just adding then just use the empty slots.