debian:~$ aticonfig --list-adapters
* 0. 04:00.0 AMD Radeon HD 6990
  1. 05:00.0 AMD Radeon HD 6990

* - Default adapter


excerpt from xorg.conf:


Section "Device"
        Identifier  "aticonfig-Device[0]-0"
        Driver      "fglrx"
        BusID       "PCI:4:0:0"
EndSection