Switchable Graphics
Select ThinkPads feature switchable graphics, where a low power consumption integrated GPU and high performance dedicated GPU is combined and you have the ability to switch between them, sacrificing either performance or battery life.
In Windows XP this switching requires a logout/login, while in Vista and Windows 7 there is support for runtime switching.
Under Linux, the switching so far had to be done by entering BIOS setup and changing between "Internal" (low power, integrated), "External" (high performance, discrete) or "Switchable" (OS selectable) options.
Depending on which Linux version you use, you could have the following effects
- On Ubuntu 8.10 (Intrepid) BIOS setting has to be either on Internal or External, not Switchable.
- On Ubuntu 9.10 (Karmic) the Integrated Intel card works with both Integrated or Switchable set
Lenovo has published a Switchable Graphics FAQ you may want to review.
Switchable Graphics and Docks
ThinkPads with switchable graphics can only drive DVI or DisplayPort outputs on Docks by using the high-performance discrete graphics card, the integrated GPU is just not attached to the DVI or DisplayPort outputs (though VGA output through the dock is possible).
Development status
David Arlie has been working on switching between GPUs without having to reboot, and changing BIOS settings. An initial version of a new driver (vga_switcheroo) has been merged in the 2.6.34 kernel. This driver allows switching between graphics cards, but requires that the Xserver is restarted. Full seamless runtime switching support will require significant Xserver work.
http://www.phoronix.com/scan.php?page=news_item&px=ODAyMg
