Memory(except on chip caches), disks, and various other peripherals arn't on the same chip in traditional servers. They're basically taking the backplane of a

Memory(except on chip caches), disks, and various other peripherals arn't on the same chip in traditional servers. They're basically taking the backplane of a motherboard and spreading it across a whole rack instead of inside a single server. Especially memory would take a latency hit if all you do is extend the "cable" length between the CPU and memory, which is why they also need a much faster interconnect.