Hard rock is generally a much louder and faster form of rock music. Guitars, drums, bass and even instruments such as the piano or violin comprise the sound of hard rock.
Some of the earliest popular bands in hard rock were Deep Purple, Cream, The Who and Led Zeppelin. AC/DC, Aerosmith and Queen would soon follow in their footsteps.
There were many hard rock bands in 1980s, including Van Halen, Guns N' Roses and Bon Jovi.
The 1990s saw a dramatic change in hard rock, as bands from Seattle like Nirvana, Pearl Jam and Soundgarden introduced "grunge" hard rock music to the mainstream. Grunge included punk rock and even heavy metal sounds.
Hard rock is still a popular form of music today, with bands such as Nickelback, Hinder and Linkin Park creating their own versions of the hard rock sub-genre. Some of the earlier bands, such as AC/DC and Aerosmith, still continue to make hard rock albums (as of 2009).