SGI Origin 350
A system consists of up to eight CPU "bricks" (3 rackmount units high each) with up to four CPUs in each brick, giving a maximum of 32 CPUs. CPU bricks are connected together via NUMAlink cables going to a central NUMAlink router or hub which is another 3U rackmounted unit. Each CPU brick has four PCI slots across two PCI busses. The first CPU brick in a system has a single PCI slot holding a BaseIO card with SCSI interfaces for two internal disks, an external SCSI port, audio I/O and a twisted pair Ethernet connection.
Other kinds of bricks are available that are dedicated to disk storage or further PCI slots. Multiple bricks are co-ordinated at startup time via an L2 controller which communicates to the bricks via USB ports. The L2 controller is an external PPC Linux unit with console, USB, modem and ethernet ports.