[ubuntu] How Ubuntu makes tear-free desktop?

view story

http://ubuntuforums.org – Hello. I've worked with Ubuntu 12.04 and Ubuntu 10.04 and was admired that there is not any tearing even "from scratch" with default video drivers. I very apprectiate Ubuntu developers for this because i hate tearing. But now i need to configure one Debian Stable (squeeze) desktop (based on Gnome too), and it has tearing. Tell me, which settings in Ubuntu are responsible for tear-free desktop. I want to configure Debian's Gnome to achieve it on opensource drivers like it's done in Ubuntu. My videocard is ATI HD 4850. (Hardware)