Minimizing the number of cases in a standard is important in dealing with hardware designed for the mass market. USB, 1394B, Fibre Channel, SATA, and SAS fit into this category. Yet common connectors can still allow for some variation when it comes to speed, and each of these connectors has multiple incarnations.
From a board interconnect view, these serial interfaces provide a valuable mechanism to link peripherals to host controllers. In fact, 1394B is more likely to be in consumer or automotive applications than in server backplanes.
USB tends to span the consumer, commercial, and industrial spaces like PCI Express. While it’s typically found on motherboards for peripheral connections, it can be used for board interconnects as with the new StackableUSB standard (see “USB Stacks Up With A Modular Industrial Form Factor”).
The other three interfaces—Fibre Channel, SATA, and SAS—sit in the storage arena. They’re quite common as board interconnects, though they’re typically limited to host motherboard to storage controller boards.
Fibre Channel is entrenched in enterprise storage and rarely shows itself in other spaces, with some exceptions. It’s often found in embedded data recording applications. And actually, it’s more of an intermediate interface since disk back ends are typically SATA or SAS drives these days, though native Fibre Channel hard drives are available.
SAS, Fibre Channel, and Ethernet come in fixed flavors. But high bandwidth can be obtained without stepping up to a faster version of the protocols by bonding channels together. This tends to happen at a slightly higher level than the approach used with PCI Express and its ilk, but the results are the same—more throughput using more cable connections.