PCI Express addendum
With the inherent limitations in the original PCI interface having become apparent, PCI Express is proposed as the natural evolution of PCI that will take the PC industry into the next decade. PCI Express has been designed to provide a standard that can be used by different manufacturers that offers enough flexibility to accommodate desktop, notebook, server, workstations, embedded devices and mobile devices . This will simplify design, giving engineers an I/O standard that can be adapted to create 3D games on high-end workstations, or even used in notebooks and other mobile devices that require low power consumption. Another possibility is creating PCs that have a modular design, making it possible for some components to be separate from the PC case and motherboard. This would be ideal in offices or homes where workspace is at a premium.

The key to this flexibility is the scalable nature of PCI Express, as well as its serial nature. Whereas PCI sent data in parallel, PCI Express is constructed from 1 all the way up to 32 “lanes”. Each lane has contained a set of differential signal pairs, one pair for transmission, and another pair for reception. This “stackable” structure makes PCI Express extremely flexible, with PCI Express x1 offering 250 MB/s transfer rate and x32 offering up to 8 GB/s! For example, manufacturers can use x1 PCI express for applications such as gigabit LAN or SATA; although x1 has the least bandwidth of all PCI Express standards, it still has almost double the rate of the old PCI bus, and is more than adequate for most hardware implementations at the desktop level. Where PCI Express really shows its strengths is when multiple lines are stacked together, giving manufacturers and developers enough bandwidth to create powerful hardware and software for desktop PCs, notebooks, severs and workstations. Indeed, it can be said that finally, after all these years, PC I/O technology has caught up with the huge advances made in processor and memory technology.

Perhaps the most exciting advance will be the replacement of the AGP slot with a PCI Express x16 slot. PCI Express x16 offers a 4 GB/s transfer rate per directional lane (8 GB/s with both lanes), almost double the current AGP standard. Indeed, game developers, graphics card manufacturers and gamers themselves are eagerly anticipating this move to PCI Express x16 as the next evolutionary step for PC gaming. VGA cards using this slot are set to hit the market now, but don’t expect the games themselves to fully utilize the new technology for at least another year.