Old-school hip hop (also spelled old skool) is the earliest commercially recorded hip hop music. It typically refers to music created around 1979. Old-school hip hop is said to have ended around 1984, due to changes in both rapping technique and the accompanying music and rhythms.
The image, styles and sounds of old-school hip hop were exemplified by figures like Grandmaster Flash, Afrika Bambaataa, DJ Kool Herc, Treacherous Three, Funky Four Plus One, Kurtis Blow, The Sugarhill Gang, Melle Mel, Super-Wolf,, West Street MobSpoonie Gee, Kool Moe Dee, Busy Bee Starski, Lovebug Starski, The Cold Crush Brothers, Warp 9, T-Ski Valley, Grandmaster Caz, Doug E. Fresh, The Sequence, Jazzy Jay, Rock Steady Crew, and Fab Five Freddy. It is characterized by the simpler rapping techniques of the time and the general focus on party-related subject matter. The lyrics were a very important part of old-school rap songs. There were however, exceptions, such as Brother D's "How We Gonna Make the Black Nation Rise", and Kurtis Blow's "Hard Times" (both released in 1980), that explored socially relevant ideas. The release of The Message in 1982 by Duke Bootee (who did nearly half the rapping and the rest by Melle Mel) and Melle Mel, although released as by Grandmaster Flash and The Furious Five, marked the arrival of hip hop as social commentary, making it possible for future artists like Public Enemy and N.W.A to create an identity based on socially conscious themes in later years. The most popular rappers from those days are N.W.A., The Wu-Tang Clan, Ice Cube, Eazy-E, Run-DMC, Dr. Dre, and many other pioneers. If not for old-school rappers, it's highly unlikely that rap would have evolved into the popular artform that it is today. Many old-school rappers are still widely respected by today's biggest hip hop artists and fans.
The very first crossover rap single, "The Breaks" (1980) is exemplary of old-school hip hop. It features a repetitive funk guitar riff, popping bassline, and party noise in the background. Kurtis Blow's playful rapping features simplistic rhyme patterns, with cadences that fall squarely on the beat, followed by breakdowns. His anthemic lyrical content retains a social conscience that is both comedic and cautionary.
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Old-school hip hop is noted for its relatively simple rapping techniques, compared to later hip hop music. Artists such as Melle Mel would use few syllables per bar of music, with simple rhythms and a moderate tempo.
Much of the subject matter of old-school hip hop centers around partying and having a good time. In the book How to Rap, Immortal Technique explains how party content played a big part in old-school hip hop: "hip-hop was born in an era of social turmoil... in the same way that slaves used to sing songs on a plantation... that's the party songs that we used to have".
As mentioned earlier, a notable exception is the song "The Message", which was written, produced and mainly rapped by Duke Bootee. It was offered to Grandmaster Flash (who led the group) and he turned it down, citing that no one wanted to hear reality, and that it was all about parties. Melle Mel however contacted Duke Bootee afterward and expressed that he did want to take part. Melle Mel rapped the verse he rapped in 1979's "Super Rappin'" on "The Message", and the rest is in fact rapped by Duke Bootee himself. Once the song was completed it was released under the banner of Grandmaster Flash and The Furious Five in order to give it some credibility. The song was a hit and introduced social commentary to hip hop. Grandmaster Flash normally does not reference that he had absolutely nothing to do with "The Message", and Duke Bootee is given no credit in documentaries or by hip hop historians. Duke Bootee solely produced (once again) and rapped "The Message II (Survival)" with Melle Mel again in 1983.
Battle rap was also a part of the old-school hip hop aesthetic. While discussing battle rapping, Esoteric said, "a lot of my stuff stems from old school hip-hop, braggadocio ethic". A famous old-school hip hop battle occurred in December 1981, when Kool Moe Dee challenged Busy Bee Starski. Busy Bee Starski's defeat by the more complex raps of Kool Moe Dee meant that "no longer was an MC just a crowd-pleasing comedian with a slick tongue; he was a commentator and a storyteller". in the documentary Beef, KRS-One also credits this as creating a shift in rapping.
Sci-fi/Afrofuturism was another theme introduced into hip hop. The release of Planet Rock in 1982 was a game-changer, like "a light being switched on." The combination of electronic percussive propulsion and Afrika Bambaataa's rap sounded like "an orchestra being rocketed into outer space." "Light Years Away", by Warp 9 (1983), produced and written by Lotti Golden and Richard Scher, explored social commentary from a sci-fi perspective. A "cornerstone of early 80's beatbox afrofuturism", "Light Years Away" is characterized as "a brilliantly spare and sparse piece of electro hip-hop traversing inner and outer space."
Freestyle rap during hip hop's old-school era was defined differently than it is today. Kool Moe Dee refers to this earlier definition in his book There's a God on the Mic: "There are two types of freestyle. There's an old-school freestyle that's basically rhymes that you've written that may not have anything to do with any subject or that goes all over the place. Then there's freestyle where you come off the top of the head". In old-school hip hop, Kool Moe Dee says that improvisational rapping was instead called "coming off the top of the head". He refers to this as "the real old-school freestyle". This is in contrast to the more recent definition defining freestyle rap as "improvisational rap like a jazz solo".
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Old-school hip hop often sampled disco and funk tracks, such as "Good Times" by Chic, when performed live in the 1970s. Recorded hip hop (such as Sugarhill Gang's "Rapper's Delight)" would use a live band to do covers of the famous breaks from the 1970s block parties. However, after Planet Rock, electro-funk (the electronic Roland TR-808 drum machine recreation of the original 1970s breakbeat sound from the now infamous block parties) became the staple production technique between 1982 and 1986 (the invention of the sampler later in the 80s and Eric B & Rakim's Eric B for President brought the original 1970s break beat sound back to hip hop, referred to today as the "boom-bap" sound). The use of extended percussion breaks led to the development of mixing and scratching techniques. Scratching was pioneered by Grand Wizard Theodore in 1977, and the technique was further developed by other prominent DJs, such as Grandmaster Flash. One example is "Adventures on the Wheels of Steel", which was composed entirely by Flash on the turntables.
Quincy Jones was an influential figure in hip hop as a record producer for Mercury Records, and eventually became its vice president, which made him popular in hip hop culture. He went on to publish Vibe magazine, which became a cornerstone in hip hop history.
Old-school hip hop typically refers to music created around 1979, however, the term may also be applied to music before this with hip-hop styles. "Here Comes the Judge" (1968) by Pigmeat Markham is often referred to as "old-school hip hop". 
Old school rap, the music of 1979 to 1983...