Suggestions on how to speed up 12.04?

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http://askubuntu.com – I use Thinkpad x100e: AMD Athlon Neo X2 1.6 GHz, RAM 4GB (3.6 GB available). I installed 12.04 64-bit (with Windows installer) on 40GB of hard disk space. I have some problem about lag speed of the OS. Can anyone suggest me how to disable or turn off any feature to increase the speed performance of Ubuntu? (HowTos)