Apart from costs and size there's could be good reasons to do this - power, inteferance, placement and cooling. Hardware specialisation (doesn't always but) ca

Apart from costs and size there's could be good reasons to do this - power, inteferance, placement and cooling. Hardware specialisation (doesn't always but) can reduce energy by allowing for more efficient designs. Just think of the power circuitry required to support all the SODIMM variants. Since soldered ram is smaller it allows greater flexibility in board design - they can be placed to avoid inteferance or to benifit thermals.