BX-133 Video Guide

The Results- An overview

The first set of cards that we tested, NVIDIA GeForce 2 GTS based cards, gave us a glimpse of what overclocking the AGP bus does. The first thing that we noted during testing was that if a card was not going to pass the tests, it usually let us know. In a very similar way to how overclocking a video card's memory or core produces artifacts on the screen (as shown in our Overclocking the GeForce 2 GTS guide), running a card in an overclocked AGP bus slot produced artifacts as well. Cards that did not finish the test began to show line-like artifacts in the green square at the bottom right hand side of the screen when running a Quake III Arena demo. This normally solid green box began to get vertical black lines running through it before the card actually failed. This serves as a good reference point to see if your card is being pushed to far by an excessive AGP bus speed.

The second item noted, as shown in the following table, is that the two cards that had sideband addressing (SBA) enabled in the card's BIOS provided for the most problems. In fact, these two cards were the only ones that failed both the 133 and 148 MHz tests. Sideband addressing was actually one of the original features to be boasted in the AGP bus. Allowing a video card to add three special extensions on the sideband channels, sideband addressing theoretically allowed for more AGP bandwidth. This feature, which is turned on or off in the BIOS depending on the video card manufacturer's choice, does not add any noticeable speed to an AGP card. To prove this, we tested the Absolute Multimedia Outrageous GeForce 2 GTS in Quake III Arena Demo001. With SBA enabled, the default state of the card, a frame rate of 114.4 FPS was recorded. When SBA was disabled using PowerStrip, the frame rate in the the same benchmark was recorded to be 114.4 FPS: the exact same speed as with SBA on.

With these results, one can not question that SBA provides no noticeable speed increase. What it does appear to do, however, is limit the functionality of a video card in an overclocked AGP bus. Sideband addressing provides for a more complex AGP bus route, meaning that there is more opportunity for failure.

To check and see if sideband addressing was enabled for an individual card, we used En Tech's PowerStrip. Not only did PowerStrip allow us to see if SBA was enabled or not, it also allowed us to turn on or off this feature. By turning off SBA on the cards that had it enabled, we achieved a 100% success rate when running the cards in overclocked AGP bus', as shown in the following table.