The Advent of PCI Express
ATI and NVIDIA Discuss Their Plans

By: Chris Angelini
March 23, 2004

ATI Chimes In
No bridge is better than one

ATI is quick to argue against NVIDIA's approach in adopting PCI Express.  According to representatives at ATI, its native implementation of PCI Express enables full performance provided by the interface, including all bandwidth and power management features.  ATI also claims its design is more economical, as individual bridge chips are expected to add somewhere around $8 to each of NVIDIA's boards.  NVIDIA counters that its pricing is already set, and there won't be a pricing change in light of the bridge chip.

There are a few other reason ATI cites for not using the bridge chip, the most prevalent of which is a possibility of higher latency caused by translating AGP to PCI Express and vice versa. The ATI solution is also "less risky" according to an ATI presentation, purportedly because the bridge chip introduces another potential point of failure.  That one's a bit tougher to argue since ATI has to pull apart its GPU to add PCI Express support, anyway. 


ATI's bridgeless solution.
In the bottom illustration, ATI is making the point that adding a bridge introduces one more potential failure point.

When asked about the procedure for adding PCI Express to existing GPUs, ATI was adamant that the cards introduced on current architectures aren't simply patched-up versions of today's processors, suggesting the possibility of other minor changes once ATI announces its complete lineup. 

Considering ATI's real-time hi-def video editing demonstration, it seems to be on track to deliver once complementary chipsets are available.

What, then, are the real implications of PCI Express?  To be quite frank, it's still too early to tell.  After all, neither NVIDIA nor ATI have cards available, though the former has already announced an entire product lineup and the latter has already demonstrated real-time HD video editing on a PCI Express platform.  As with each of the past revisions to AGP, it will undoubtedly take quite a while for software to begin exploiting the bandwidth advantages of PCI Express.  Then again, representatives at ATI claim that the video editing software they demonstrated will be available sooner than one might expect. 

At some point, the lofty bandwidth numbers that PCI Express boasts will probably be of utmost significance.  Right now, however, there is little in the way of software capable of taxing AGP 8x, much less its faster successor.  We'll certainly have to wait until hardware materializes, but even then, interface considerations will probably play a secondhand role in determining the performance of next-generation's round of high-end graphics cards.

The more important market for PCI Express is mobile graphics, where low power, small size, and high performance are all prized attributes.  The ability to turn lanes on and off according to system needs should prove useful in stretching battery power, and mobile PCI Express graphics boards should be significantly smaller than their AGP counterparts.  In recent discussions with NVIDIA and ATI, both companies have confirmed with confidence that PCI Express will exist in mobile trim by the end of 2004, and in native form, no less.

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