DMA (direct memory access), how do you do it?

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I just have a question regarding to DMA, direct memory access. My desktop computer is about 3 years old, and I have it upgraded from Windows Vista to Windows 7 recently. I read about you could increase the speed by a lot if you set up the DMA right from your hard drive to RAM. So, I was trying to tweak it on my PC, but I couldn't find whether my hard drive is support DMA or not. So, how do you set up DMA on your hard drive. Is it from device manager? I couldn't find the hard disk icon on the device manager. Anyone can help?