Heavy Metal is a sub-genre of the "Metal-family" (for ex. heavy metal, black metal, death metal...). Metal derives directly from blues and rock, even if in some sub-genres there is an evident influence of classical music. So, even if heavy metal and black metal belong to the same family, there is an effective difference between them. Heavy metal is mainly blues-based, with pentatonic scales and a blues-like song structure; black metal is based on classical music, even if at a first glance it seems to be only distorted guitars playing very fast a repeating melody.
Heavy Metal developed out of Sixties Rock and Blues when musicians started to exploit the opportunities of the electrically amplified guitar to produce a louder, more discordant sound. The term "Heavy Metal" was used as a jibe initially but was quickly adopted by its adherents. Bands such as Led Zeppelin and Black Sabbath specialised in a "stripped down" sound in which the Blues inheritance was reduced. The influence of Jimi Hendrix should not be discounted though, acting as both an innovator in the technical capabilities of the electric guitar and a bridge between black music and white European rockers. Some of the original Heavy Metallers joked that their simplified sound was more the result of limited ability rather the desire to innovate.
The American band Grand Funk Railroad epitomised early heavy metal, and set an alternative benchmark in which the volume of the music was seen as the important factor rather than its musical qualities. Douglas Adams neatly satirised this propensity for excessive volume in The Hitch Hikers Guide to the Galaxy with the fictional rock band Disaster Area - creators of the loudest sound in the known universe. It should be noted however, that Adams was satirising Pink Floyd stage shows specifically - rather than metal in general.
The energetic and vitalised music soon found an audience and rapidly spread to the United States through extended touring. American musicians swiftly absorbed the agitated style and began to restore a more technically refined element as well as the Blues element.
An element to be pointed out is that "black" or "death" metal is considered by the artists playing that kind of music to be white/European, in opposition to the blues-based rock, wich derives from afro-american music (obviously most of the black or death people are not racists).
Sub-genres of heavy metal are numerous: including "neo-classical" metal, whose most renowned artist is the Swedish axeman Yngwie J. Malmsteen. In neo-classical metal, the traditional toolbox of metal song-writing is used, but with a twist: all of it takes place in a structure that is heavily influenced by baroque music. The chord progressions, arpeggios, broken chords, and speedy scale runs of neo-classical metal are borrowed for the most part from Johann Sebastian Bach, Antonio Vivaldi and Niccolo Paganini. Although Malmsteen is the most well-known proponent of this evolution of metal, however, classical elements used in heavy metal and hard rock date back to Ritchie Blackmore of Deep Purple and Eddie Van Halen's innovations in the 1970s.
The most used lineup for metal is: a drummer, using a double base-drum; a bass guitar; a rhythm guitar; a lead guitar; a singer; sometimes a keyboard player can be found. The singer uses a clean, often very high, voice. Guitar playing is very important in heavy metal. Intricate solos and riffs are a big part of heavy metal music. Guitarists use sweep-picking, tapping and similar techniques to obtain amazing fast playing. The black and death metal scene uses distorted and guttural voices (for example try to listen to some songs of the californian band Deicide). Generally it's hard to understand what the singer is "singing", since the text is considered to be too crude to be spoken out clearly (try to listen to Cannibal Corpse). See death metal for more info.