If you have samsung 840 evo then go to samsung website and download samsung magician app. From it you can optimize your pc settings to work for 840 evo and also it will tell you if AHCI is enabled or not.
Yeah I also know it won't do huge amount but as he said he don't know if he has enabled AHCI or not and he don't know how to do it. That's why I referred him the app.