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Fibre Channel (FC-AL)
You probably know that parallel SCSI is a high-end hard disk interface that is an alternative to the ubiquitous IDE/ATA. However, you may not realize that regular SCSI itself has a "big brother" of sorts. This interface is called Fibre Channel. The name comes from the fact that it was originally designed to operate over fiber-optic physical channels; copper wiring is now also supported. (The correct spelling is also "Fibre", not "Fiber"; this reflects the standard's European origins.) Like IEEE-1394, Fibre Channel is actually defined as part of the SCSI-3 family of standards, so it really is sort of a "sibling" to conventional SCSI. Sort of. :^)
Like regular SCSI, Fibre Channel is a collection of protocols and options, and it would take some time for me to explain them all in detail, which I'm not going to do at present. The current implementation that is in use is a subset of Fibre Channel called Fibre Channel Arbitrated Loop or FC-AL. FC-AL allows many servers and storage devices to be connected into what is essentially a "storage network". This configuration offers flexibility, performance and reliability advantages to high-end systems.
Despite being a serial interface, FC-AL allows for throughput of up to 4 Gbits/s, with future versions likely to increase this. One of the primary benefits of Fibre Channel is that when using fiber optic connections, devices can be separated by up to 10 kilometers--yes, 10,000 meters. Even with copper connections, 30 meters is the limit, which is pretty good compared to other interfaces.
So if Fibre Channel is so great, why isn't it used by PCs? The main reasons are cost, and the lack of necessity. FC-AL is currently used almost exclusively on servers--and groups of servers working together. It's a high-end interface that you aren't likely to run into in your personal system, at least for now. I did want to mention it, however, so you know it is out there. :^) I will provide more explanation of Fibre Channel in the future if and when it becomes more widely implemented. In the meantime, for more information on this technology, see the Fibre Channel Industry Association web site.