Author: Manfred Schmitz, CTO MEN Mikro Elektronik
With the parallel PCI bus disappearing, a standard PC is now based on a simple star topology. The CPU chipset at the system's center controls peripheral devices and components through point-to-point connections. This allows high data rates, while no device needs to concede bandwidth to another.
This simple structure is completely adequate for a standard computer. But even for multiprocessing systems based on Ethernet, this architecture is often sufficient if a suitable Ethernet switch is accommodated in the system slot. This switch can be implemented as a mezzanine on the system slot.
Of course, you might as well populate the system slot merely by a switch, which itself has no computer functionality.
In another interesting variety, the computer in the system slot not only takes care of the central Ethernet connection but also functions as a NAS (Network Attached Storage). SATA (RAID) is also connected as a star. Certainly, all CPU boards can be identical, but only the CPU in the system slot uses its RAID controller and also has a plug-on switch. The additional CPUs in the peripheral slots have neither a switch nor a RAID function in the system.
In all, a standard CompactPCI Serial backplane has up to 9 slots, which lets you combine CPUs and hard disks as needed. A customized backplane permits to implement up to 8 Ethernet slots and 8 hard disk slots without any further bridge or switch boards.
The simple star architecture allows to solve complex tasks at a competitive price. For more demanding tasks, the CPCI-S.0 CompactPCI Serial standard also offers a solution using an Ethernet mesh (see next article).