Hard rock

Hard rock (also referred to as heavy rock) is a variation of rock music which has its earliest roots in mid-1960s garage and psychedelic rock. It is typified by a heavy use of distorted electric guitar, bass guitar, keyboard and drums. The term "hard rock" is often used as an umbrella term for genres such as grunge or metal and in order to distinguish them from pop rock. Hard rock is strongly influenced by blues music; the most frequently used scale in hard rock is the pentatonic, which is a typical blues scale. Unlike traditional rock and roll (which takes elements of the "old" blues), hard rock incorporates elements of "British blues", a style of blues played with more modern instruments such as electric guitars, drums, keyboard and electric bass. A notable departure from traditional blues forms is that hard rock is seldom restricted to the I, IV, and V chords prevalent in twelve or sixteen bar blues, but includes other chords, typically major chord rooted on tones of the minor... full article at wikipedia