Hard rock is a variation of rock and roll music which has its earliest roots in early-1960s garage and psychedelic rock. It is typified by a heavy use of distorted electric guitars, bass guitar and drums. The term "hard rock" is often used as an umbrella term for genres such as punk and grunge in order to distinguish them from the more radio-friendly pop rock genre.
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, keyboards 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 12- or 16-bar blues, but includes other chords, typically major chords rooted on tones of the minor scale.
The term "hard rock" is often applied to many styles of rock music, their only common feature being that they deviate from pop rock, though this is generally incorrect. Two such examples are punk rock and grunge. Punk rock uses a faster tempo and fewer riffs (often using power chords).
The predominant instruments in hard rock are the electric guitar, bass guitar, and drums. The role of the guitarist is very prevalent in hard rock. Most hard rock bands comprise of two different types of guitarist: lead guitarist and rhythm guitarist. The lead guitarist plays the solos, riffs and fills. Speed-enhancing techniques such as alternate picking, sweep picking and tapping, are used by hard rock lead guitarists to maximize the speed of their solos and riffs. The role of the rhythm guitarist is to compliment the lead guitarist and provide rhythmic and harmonic accompaniment to the other instruments in the band. The bass guitarist and drummer's role are important to the structure of hard rock music; the bassline outlines the harmony of the music while the drums sustain the rhythm of the music.
 Differentiation from heavy metal
During the 1970s, hard rock inspired a new genre of music known as "heavy metal." The emergence of this genre has led to confusion between hard rock and heavy metal bands, as the distinctions between the two are usually subtle, and the distinction often comes down to a band's image, rather than its songs. The two genres have some crossovers, for example; heavy metal pioneers, such as Black Sabbath, Led Zeppelin and Deep Purple, are often considered both heavy metal and hard rock, whereas, bands such as AC/DC, Aerosmith,Thin Lizzy,Bon Jovi,Nazareth,Van Halen and KISS, are normally referred to as hard rock.
To further the confusion, the most popular heavy metal subgenre of the 1980s, glam metal, was known to take influence from both the pioneering heavy metal acts and other hard rock groups, such as Alice Cooper, KISS and Aerosmith, etc. Both KISS and Aerosmith subsequently went on to experiment with glam metal.
From a musical point of view, heavy metal tends to interpret the basic syncopated jazz rhythm of an eight and two sixteenth carried on a ride cymbal with a swing feel down to the bass line with a literal "straight up" feel. Thus the "dum da da dum da da dum" bass line is a standard basis for the heavy metal sound (as heard, for example, in Black Sabbath's song Heaven and Hell during the verses, or in Iron Maiden's song Flight of Icarus. Another good example is to listen to the difference between how the song Helter Skelter is played by the original writers, The Beatles and the interpretation as played by Mötley Crüe.
The primary difference between glam metal and heavy metal is in the lyrics. Heavy metal lyrical content extends from "reality lament" tone of blues, discussing serious, provocative or philosophical ideas. Glam metal, on the other hand, extends from its more "fantasy escapist" tones of pop music, and tends to focus more on parties, having a good time, relationships.
 Early years (1960s)
As stated, one of the major influences of hard rock is blues music, especially British blues. British rock bands, such as The Rolling Stones, The Beatles, The Yardbirds, The Who and The Kinks, modified rock and roll, adding to the standard genre; harder sounds, heavier guitar riffs, bombastic drumming and louder vocals. This sound created the basis for hard rock. Early forms of hard rock can be heard in the songs "Helter Skelter" and I Want You (She's So Heavy)" by The Beatles, "I Can See for Miles" by The Who, and "You Really Got Me" by The Kinks.
At the same time, Jimi Hendrix, produced a form of blues-influenced psychedelic rock, which combined elements of jazz, blues and rock and roll, creating a unique genre. He was one of the first guitarists to experiment with new guitar effects like phasing, feedback and distortion.
Hard rock emerged from British groups of the late-1960s, such as Black Sabbath and Led Zeppelin, who mixed the music of early British rock bands with a more hard-edged form of blues rock. Led Zeppelin's eponymous first album, Led Zeppelin I (1969), is an example of blues rock which represents the beginning of the hard rock genre. The blues origins of the album are clear, and a few songs by well-known blues artists are adapted or covered within it. Later, Deep Purple entered the hard rock scene with the albums, Shades of Deep Purple (1968), The Book of Taliesyn (1968), and Deep Purple (1969).
 First era (1970s)
Led Zeppelin's third album, Led Zeppelin III was more progressive rock-oriented than their second, but the heavy aspects of their music remained. In 1970, Black Sabbath released what is considered the first heavy metal album, Black Sabbath. Black Sabbath's music was revolutionary even in hard rock; it was typified by dark lyrics, hard riffs and a heavy atmosphere, transforming the current hard rock into to an early form of heavy metal.
Deep Purple's transformation of hard rock continued with their album, Machine Head, considered (along with Black Sabbath) as one of the first proto-metal albums. The Machine Head song, "Highway Star", is considered the first speed metal song. Another band, Nazareth, provided a blend of hard rock which commercialised the genre further with their best selling album, Hair of the Dog, which in turn, influenced numerous other bands.
During the 1970s, hard rock developed a variety of sub-genres. In 1972, Alice Cooper made the first "shock rock" album, School's Out. The following year, Aerosmith, Queen and Lynyrd Skynyrd released their eponymous debut albums, demonstrating the broadening directions of hard rock. In 1974, Bad Company released its debut album, and Queen released its third album, Sheer Heart Attack, with the track Stone Cold Crazy influencing later thrash metal artists, such as Metallica and Megadeth. Queen used layered vocals and guitars and mixed hard rock with glam rock, heavy metal, prog rock, and even opera. KISS released their first three albums Kiss, Hotter Than Hell and Dressed To Kill, in a little over a year, achieving their commercial breakthrough with double live album Alive!. In the mid-1970s, Aerosmith released the ground-breaking albums Toys in the Attic and Rocks which incorporated elements of blues and hard rock and would later influence rock artists as diverse as Metallica, Guns N' Roses, and Mötley Crüe.
With the death of Tommy Bolin in 1976, Deep Purple disbanded. In 1977, the lead singer of Lynyrd Skynyrd, Ronnie Van Zant, died in a plane crash, disbanding the group. A year later, The Who's drummer, Keith Moon died in his sleep via an overdose. With the rise of disco in the U.S. and punk rock in the UK, hard rock began to lose popularity. Disco appealed to a more diverse group of people and punk seemed to take over the rebellious role that hard rock once held. Meanwhile, Black Sabbath moved away from the darkness of their early work with albums such as Technical Ecstasy.
Van Halen, another important group in hard rock, formed in 1978. Their music was based mostly on the guitar skills of Eddie Van Halen, the lead guitarist. The song, "Eruption" from the album Van Halen, demonstrated Eddie Van Halen's technique and was very influential.
In 1979, the differences between the hard rock movement and the rising heavy metal movement were highlighted when the Australian hard rock band, AC/DC, released its second-biggest album, Highway to Hell. AC/DC's music was based mostly on rhythm & blues and early-1970s hard rock, with the group explicitly repudiating the "heavy metal" tag.
 Second era (1980s)
Back in Black
by AC/DC is the second most sold album in the world.
In 1980, Led Zeppelin disbanded after the sudden death of drummer John Bonham. Bon Scott, the lead singer of AC/DC, also died in 1980. With these deaths, the first wave of "classic" hard rock bands ended. Some bands, such as Queen, moved away from their hard rock roots and more towards pop. AC/DC recorded the album Back in Black, with their new lead singer, Brian Johnson. Back in Black is the fifth highest-selling album of all time in the U.S. . By being so successful, AC/DC and Van Halen helped make possible the rise of more radio-friendly hard rock.
In 1981, the U.S. band, Mötley Crüe, released Too Fast for Love, which set the basis for the rising genre of glam metal. A year later, the genre grew, especially thanks to Twisted Sister and Quiet Riot. Quiet Riot's Metal Health is the first heavy metal album ever to reach #1 on the Billboard United States chart.
Def Leppard, an English hard rock band, released in 1983 the album Pyromania, which reached #2 in the American charts. Their music was a mix of glam rock, heavy metal, classic rock and Album Oriented Rock, which influenced many 1980s hard rock and glam rock bands.
In 1983, Mötley Crüe released the album, Shout at the Devil, which became a huge hit. Van Halen's album 1984 became a huge success, hitting #2 on the Billboard album charts. In particular, the song "Jump" reached #1 on the single chart and is considered one of the most popular rock songs ever written. However, 1984 was also their first to include the use of keyboards and synthesizers, marking a shift away from their original guitar-orientated style.
In 1987, the most notable successes in the charts were Appetite for Destruction by Guns N' Roses, and Hysteria by Def Leppard (which reached #1 on Billboard's album chart), Mötley Crüe's Girls, Girls, Girls and Whitesnake's 1987. Dinosaur Jr and Sonic Youth achieved underground success in the U.S, and would later reach the mainstream in the '90s. In 1988, Skid Row formed. Their first album, Skid Row, was released in 1989. Mother Love Bone had a flamboyantly influential, yet brief, career before evolving into Pearl Jam.
 Third era (1990s-present)
The early 1990s were at first dominated by Guns N' Roses and Metallica. The multi-platinum releases of Metallica's "Black Album" and Guns N' Roses' Use Your Illusion I and Use Your Illusion II in 1991 showcased this popularity. But as these bands' acts and albums became more decadent and self-indulgent, their popularity waned, and by 1992 a new form of hard rock, known as grunge, emerged. Some grunge bands became very successful, such as Nirvana, Pearl Jam, Soundgarden, and Alice in Chains.
While their success was often pitched in the media as a punk rock reaction to arena rock and glam metal, the bands were hardly antagonistic to the heavy metal genre in general. Soundgarden and Nirvana were influenced by much 1970s and 1980s metal, while Alice in Chains were arguably a heavy metal band themselves. Several other notable bands include: The Screaming Trees, The Melvins, Mudhoney, and a few non-Seattle-based bands such as Stone Temple Pilots, Nudeswirl, Prong and Hum. In the UK, bands like Swervedriver, Catherine Wheel and Ride demonstrated that guitar heroics could be incorporated into songs that lacked the often-misogynistic content of '70s and '80s hard rock bands.
As the popularity of artists such as Metallica continued from the 1980s into the 1990s, some other bands had begun to fuse metal with a range of eclectic influences. These bands came to be known as alternative metal artists, a subset of alternative rock. Some, such as Primus, Red Hot Chili Peppers, Rage Against the Machine, Living Colour and White Zombie fused funk with metal styles, though most of these bands actually formed in the '80s. Faith No More/Mr. Bungle fused many genres with hard rock, ranging from rap music to soul. Helmet and The Afghan Whigs were also successful experimental hard rock bands. The Darkness's retro glam-metal influences helped propel them to the upper realms of the charts in the early 2000s.
 See also