were disconnected thematically; they were separate unto themselves. But by using song lyrics, Hollywood gave his rhyme an inherent flow and theme. This was quickly noticed, and the style spread. By the end of the 1970s, artists such as Kurtis Blow and The Sugarhill Gang were starting to receive radio airplay and make an impact far outside of New York City, on a national scale. Blondie's 1981 single, "Rapture", was one of the first songs featuring rap to top the U.S. Billboard Hot 100 chart. Old-school hip hop Old school rap (1979–84) was "easily identified by its relatively simple raps" according to AllMusic, "the emphasis was not on lyrical technique, but simply on good times", one notable exception being Melle Mel, who set the way for future rappers through his socio-political content and creative wordplay. Golden age Golden age hip hop (the mid-1980s to early '90s) was the time period where hip-hop lyricism went through its most drastic transformation – writer William Jelani Cobb says "in these golden years, a critical mass of mic prodigies were literally creating themselves and their art form at the same time" and Allmusic writes, "rhymers like PE's Chuck D, Big Daddy Kane, KRS-One, and Rakim basically invented the complex wordplay and lyrical kung-fu of later hip-hop". The golden age is considered to have ended around 1993–94, marking the end of rap lyricism's most innovative period. Flow "Flow" is defined as "the rhythms and rhymes" of a hip-hop song's lyrics and how they interact – the book How to Rap breaks flow down into rhyme, rhyme schemes, and rhythm (also known as cadence). 'Flow' is also sometimes used to refer to elements of the delivery (pitch, timbre, volume) as well, though often a distinction is made between the flow and the delivery. Staying on the beat is central to rap's flow – many MCs note the importance of staying on-beat in How to Rap including Sean Price, Mighty Casey, Zion I, Vinnie Paz, Fredro Starr, Del The Funky Homosapien, Tech N9ne, People Under The Stairs, Twista, B-Real, Mr Lif, 2Mex, and Cage. MCs stay on beat by stressing syllables in time to the four beats of the musical backdrop. Poetry scholar Derek Attridge describes how this works in his book Poetic Rhythm – "rap lyrics are written to be performed to an accompaniment that emphasizes the metrical structure of the verse". He says rap lyrics