Rage3D.com reports that ATI has written some documentation about their AGP detection utility. They explain what it is, why it's there and answer a few FAQs.
Does SMARTGART disable all AGP support including AGP reads, AGP writes, and AGP fast writes)?
No. SMARTGART tests the functionality of each AGP command and determines if your system is capable of supporting each one, and will only enable it if system stability is maintained. Please note that SMARTGART does not disable or turn off AGP support in your actual hardware; SMARTGART only ensures that the ATI CATALYST driver will not use an AGP function that has been deemed to be unstable.
ATi SmartGART AGP detection utility whitepaper
Does SMARTGART disable all AGP support including AGP reads, AGP writes, and AGP fast writes)?
No. SMARTGART tests the functionality of each AGP command and determines if your system is capable of supporting each one, and will only enable it if system stability is maintained. Please note that SMARTGART does not disable or turn off AGP support in your actual hardware; SMARTGART only ensures that the ATI CATALYST driver will not use an AGP function that has been deemed to be unstable.
ATi SmartGART AGP detection utility whitepaper
