The S/390 series mainframes (from IBM) are extremely big and extremely black. Think TMA-1 black. A fully configured model weighs several tonnes and draws >> 100kW of power. Oh, and they can saturate OC-48 lines rather easily.
I'd love to have one in my apartment, but the power bill would be nothing short of insane, and I doubt the floor (to say nothing of the air conditioner) could handle the load.