New features (continued)

Unfortunately, there are no more enhancements affecting 3D games, the remaining onces affect professionals.

Like, for example, the implementation of a hardware-enforced cache coherency, ensuring the integrity of the cache's data and trying to prevent and fix (one-)bit errors. There are actually two different levels: Inside the AGP-Aperture and outside of it. The AGP-Aperture is a contiguous region in the computer's main memory, where an AGP adress is being re-mapped to a different physical memory adress using the GART (Graphics Aperture Re-Map Table). Outside of this AGP-Aperture, cache coherency is hardware-enabled and irreversible. It has to be implemented by the core-logic, in other words the motherboard's chipset. Therefore, major differences between the various chipsets may exist.
Inside the AGP-Aperture, cache coherency is not hardware-enabled, but optional. It has to be enabled by software, specifically the driver. Part of the AGP 3.0 specification is the appendix with instructions, how to implement this feature. Thanks to the cache coherency protocol, the AGP-Aperture finally can be used for more than just swapping textures.

While this might sound rather interesing, even for the gaming community, chances are, that video card manufacturers will never ever make use of this feature for home user products. First of all, modern video cards have enough on-board RAM to circumvent swapping. And second, ensuring the integrity has a negative impact on performance. However, the AGP 3.0 specification doesn't even give an estimate of how much performance this feature costs, all one can read is:

"The performance of hardware-enforced coherency schemes varies between platforms."

Another quite interesting feature, which presumably will only arrest attention of professionals, is the isochronous streaming protocol. AGP was defined as an asynchronous standard, a bandwith saving implementation at part load. A huge drawback though is the data inconsistency at full load, a constant flow of data is almost impossible to realize.
That's why Intel specified the isochronous streaming protocol in AGP 3.0. In contrast to an asynchronous protocol, the isochronous protocol defines a fixed delay between two data transfers. Since real-time performance expectations continue to scale every year, isochronous streaming becomes more and more important. Games and 3D applications will not benefit from this feature, full screen videos certainly will.
This is another feature, controlled and enabled/disabled by the AGP core logic (motherboard chipset).