Why my Dell Studio 1555 getting over heated in Ubuntu 11.10?

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http://askubuntu.com – But when i use Windows 7 it is so silent i barely hear any sound from fan. I'm using standard graphics card drivers released by Ati i'm not using additional video drivers which are open source. Windows 7 is so hardware efficient it is running so efficiently on 5 years old laptop & Linux is struggling to run efficiently on it. I thought Linux's were more efficient than Windows but Ubuntu proved me wrong.Don't suggest me to use Ubuntu 12.10 because graphics drivers are not available for my Ati 45xx graphics card.Don't tell me switch to older Ubuntu versions i faced the same problems there al (HowTos)