Is the Raspberry Pi RAM located inside the Broadcom SoC or outside of it?
If it's located outside, what's the peripheral responsible for accessing this memory?
It's not really inside the SOC, as it is a separate component, but on A/B/+ models is stacked on top of the SoC, which is why the processor isn't labelled "Broadcom" (instead, probably "Samsung", who make a lot of low power mobile memory). Apparently on the Pi 2 this isn't the case -- the RAM is on the bottom of the board.
Elinux has a diagram of this which has no specific license so hopefully I'm okay linking it here. This refers to an A/B and only indicates 256 MB, but the + is the same in that regard:
The Raspberry Pi RAM is mounted on top of the SOC. It's called PoP (Package on Package).
The Pi2 and Pi3 are different. They have 1GB of RAM located on the underside of the board.
My Pi2/Pi3 RAM chips are marked ELPIDA B8132B4PB (a 168-Ball Embedded LPDDR2 SDRAM).