What is the PCI Express interface and what it can (and cannot) do for you and your PC?

For those who haven't heard of it, the short explanation of PCI Express is that it's a new interface that can go far beyond the speed of current AGP and PCI buses.

This new interface was designed to accommodate the ever-increasing speeds of PC input/output devices. Faster products and technologies on the horizon will enable advances like 10-GHz and faster CPU speeds, faster memory, speedier graphics cards, quicker storage, and other high-speed devices, plus networking beyond gigabit speeds. But current systems built with the aging PCI interface don't provide the higher bandwidth you'll need to run these faster products.

That's where PCI Express, or PCI-E, saves the day. Theoretically, it can boost the speed of a computer's PCI and AGP buses -- and also the PCI-X bus that's mainly used in servers. I say theoretically because we have yet to get our hands on PCI-E peripherals or motherboards. The new motherboards are slated to appear in a couple of months to coincide with the launch of graphics boards and other products equipped with this interface, according to Intel.

Today's typical PCI bus accepts devices like network cards and sound cards and runs at 133MB per second in one direction. PCI-E can send and receive data at the same time; and it decreases the number of wires used to connect each card. PCI cards in current desktop PCs require 32 wires, whereas an x1 PCI-E card uses only four. The x indicates a lane, or a grouping of four wires. Initially, PCI-E cards will be available in four different types of groupings: x1, x4 , x8, and x16. Each four-wire grouping would allow up to 250MB per second of sustained throughput, yielding up to 4GB per second for each direction with an x16 PCI-E card.

The cards will also be hot-swappable, an added bonus.

Some answers to your questions

Q. Will PCI-E cards drive down the insanely high cost of premium AGP graphics cards?

A. Don't bet on it, says Brian Burke, a representative for graphics chip maker NVidia Corp. "The two are not compatible, so there will be demand for both for some time," he explains. "If anything, I would expect a premium for PCI Express cards, as it is newer technology."

Q. What about power?

A. Good question. AGP slots can deliver only 25 watts. But faster cards often need more wattage, so they'll take up an extra slot to draw more power. PCI-E slots provide 75 watts, three times as much. So expect graphics cards to be super speedy. Unfortunately, games and other software to take advantage of the new interface aren't around yet, and it'll be some time before any of that appears.

Q. Will all PCs carry only PCI-E slots in the future? What about all of my other cards?

A. Please don't panic. Most new systems in the near future will likely provide only a couple of PCI-E slots and leave the other slots intact to accommodate existing cards, according to Jim Pappas, Enterprise Initiatives director at Intel Corp. He says that PC manufacturers will slowly phase out the old slots and phase in the new ones.

We can expect lots of things from this new interface -- but don't expect it to clean your bathroom, wash your clothes, or leave a minty-fresh aftertaste in your mouth.