3GIO--or now "PCI Express"--is a radical break with the system buses of the past, which gained power mainly through increasing parallelism--moving data 8, 16, 32, or more bits at a time. Although even more massive parallelism is possible, it's hard to manufacture and implement economically because of all the separate pins, connectors, wires, and traces, and because timing issues get harder and harder to manage as speeds climb.

PCI Express is designed to overcome these problems. It's actually a high-speed serial bus that only requires two wires or traces to complete a circuit and yet can run at extremely high speeds--up to 10 GHz, as opposed to the approximate 1-GHz practical limit for conventional parallel bus models.

But it's called PCI Express for a reason: Intel's spec defines what's mainly a hardware change that will result in simpler motherboard and peripheral designs, but that still will use the classic PCI driver model on the software side. This means that any operating system that works with PCI--and that's essentially all current operating systems--will also be able to work with PCI Express.

Interest in PCI Express is reaching critical mass with a worldwide series of technical seminars scheduled for April ( http://www.pcisig.com/ events/expresstour ). Intel predicts that initial PCI Express designs for commercial components will be ready for testing later this year ftp://download.intel.com/ technology/3GIO/downloads/ PCI_EI_PCB_Guidelines.pdf .

When it's finally productized, PCI Express will probably first appear on high-end servers, then migrate downward. When that happens, and when it combines with the other advances mentioned elsewhere in this article, a whole new class of PC will emerge.

We'll come back to this in a moment, but there are several other legacy components to look at first.

Moving Hard Dive Data
If you look again at the photo of the original IBM AT we presented earlier, you'll note that the hard-drive cables and connectors look very familiar. Although the AT's hard-drive controller was on a separate plug-in card rather than being built onto the motherboard, the basic hard-drive bus technology was similar to what's still in use today: A wide, parallel-conductor ribbon cable carried the data between the drive and the controller. In fact, all of today's ATA drives are called that because they use this same basic legacy-based "AT Attachment" technology you can see in that 20-year-old photo.

The original AT drives had a theoretical maximum data-transfer rate of 4.2 Mbytes per second; today's top-of-the-line ATA-133 drives have a theoretical maximum data-transfer rate of 133 Mbytes per second. But with that, there's not a lot of room for growth--the classic ribbon-cable, parallel-conductor ATA bus has just about reached its practical maximum.