Section "Device"
  Identifier "devname"
  Driver "ati"
  ...
EndSection
ati is an Xorg wrapper driver for ATI video cards. It autodetects whether
  your hardware has a Radeon, Rage 128, or Mach64 or earlier class of chipset,
  and loads the radeon(4), r128(4), or mach64 driver as appropriate.
The ati driver supports Radeon, Rage 128, and Mach64 and earlier chipsets
  by loading those drivers. See those manpages for specific cards supported.
Please refer to xorg.conf(5) for general configuration details, and the specific
  card driver for driver configuration details.
Xorg(1), xorg.conf(5), Xserver(1), X(7), r128(4), radeon(4)
See the individual driver pages for authors.