Wikipedia
hdparm is a command line program for Linux to set and view ATA hard disk drive hardware parameters. It can set parameters such as drive caches, sleep mode, power management, acoustic management, and DMA settings. GParted and Parted Magic both include hdparm.
Changing hardware parameters from suboptimal conservative defaults to their optimal settings can improve performance greatly. For example, turning on DMA can, in some instances, double or triple data throughput. Unfortunately at present there is no reliable method for determining the optimal settings for a given controller/drive combination, except careful trial and error; nor is there yet any central database that collects and shares the combined experience of hdparm users.
hdparm has a more serious drawback: it can crash a computer and make data on its disk inaccessible if certain parameters are misused. Out of approximately sixty-seven parameters, several are dangerous and could result in "massive filesystem corruption" when used indiscriminately.