Pointing to 1979 as the start of rap as it is now known, Toop writes that the first rap records were "the tip of an iceberg--under the surface was a movement called hip-hop, a Bronx subculture, and beneath that was a vast expanse of sources reaching back to West Africa."

For Toop and other rap historians, the roots of the music stretch back through a long and surprisingly varied set of characters and movements. Toop's list includes more than two dozen cornerstones, from the lively boasts of Bo Diddley and Muhammad Ali to street groups and prison songs.

Unlike rock fans, who argue endlessly over the identity of the first true rock hit, rap fans generally point to a single record as the key beginning: the Sugarhill Gang's "Rapper's Delight."

The novelty, released by New Jersey's Sugarhill Records in 1979, only made it to No. 36 on the national charts, but it opened a door for other rappers in the Bronx.

Among those who stepped forward was Joseph Saddler, whose turntable skills helped bring a new sophistication to rap. As a kid, Saddler--who latter dubbed himself Grandmaster Flash--loved music, but records frustrated him. Rather than listen to them all the way through like everyone else, Saddler picked out the best parts and imagined how they would sound together.

By his mid-teens, he had begun to create his own records by plugging two turntables into the same speaker and playing them for neighborhood kids in the park. This twin-turntable effect enabled him to switch from one record to the other: a 10-second bass line from a James Brown record, a 15-second drum explosion from a Chic single, and so forth.

Fascinated by what Saddler was doing, other teens got into the act--either dancing to the music or rapping to it.

Seeing the success of "Rapper's Delight," Flash and his allies in the Furious Five went to Sugarhill Records and released a landmark record in rap.

Hailed as 1982's single of the year by both The Times and the New York Times, "The Message" was a stark tale of ghetto alienation that demonstrated that rap was not simply an echo of the fluffy disco era. Sample lyrics: "It's like a jungle sometimes / It make me wonder / How I keep from going under."

Grandmaster Flash and the other early rap heroes failed to step forward with consistent product or dynamic stage shows, however, and rap remained a rather limited black music experience until 1983, when two brothers from Queens entered the scene.

There are debates over who has been more important in furthering rap: Russell Simmons,who brought marketing and management skills to the virgin field, or his brother Joseph, who put together the first superstar rap act, Run-D.M.C.

Unlike many of the rap pioneers, they weren't from the Bronx or the ghetto. Raised in suburban Queens, they were sons of a supervisor of attendance for the New York City school system.

Russell got into rap by producing live rap shows and eventually managing some of the better acts, including Kurtis Blow. Today, he runs Def Jam Records--whose acts have included Public Enemy, the Beastie Boys and L.L. Cool J--and Rush Management, which represents dozens of rap acts, including Run-D.M.C., Public Enemy, Slick Rick and De La Soul.

"There was a lot of resistance to rap in the record business in the beginning, but independent labels pushed for it because it was something they could build on," Russell said in 1986. "That's how most independents get started. . . . With things that major labels don't own or care about."

Joseph Simmons was such a natural rapper that he was opening shows promoted by his brother while still in his early teens. He eventually put on his own shows at the park near his house. While studying mortuary science in college, he wrote the song that became another early rap classic, "It's Like That." The record, which is in the social-realism tradition of "The Message," sold 500,000 and pushed Run-D.M.C. into the forefront of rap.

Not only did the trio make more consistent albums than their rap rivals, but Run-D.M.C. had a greater pop-rock sensibility than its contemporaries. Without sacrificing rap's black base, Run-D.M.C. reached out to a white audience that had previously ignored rap. The group also adopted a catchy, vaguely gangster-like image incorporating black hats and clothing. The idea wasn't to make people think they were gangsters. They just thought it looked cool.

Despite the trio's wholesome messages (down with drugs, up with education), the gangster image was picked up by the media when violence broke out at a few of the group's shows and has remained a cloud over the rap industry.

When 41 fans were injured during an outbreak of gang violence at a Run-D.M.C. concert in 1986 at the Long Beach Arena, Joseph Simmons said gang violence had nothing to do with rap--that it was a symptom of larger problems in the city. For many Los Angeles residents, that violence indeed was one of the first dramatic signs of the extent of the gang problem.

Meanwhile, Run-D.M.C.--with assistance from record producer and then Def Jam co-owner Rick Rubin--added a harder edge to its music. A remake of Aerosmith's "Walk This Way" broke through to the white rock market in a big way. The single--named record of the year by the Times and the Village Voice critics' poll--reached No. 4 on the pop charts and helped push the trio's "Raising Hell" album past the 4 million sales mark.

The Beastie Boys, also working with Rubin, made an even stronger move into the rock audience with their album "Licensed to Ill." The collection, which also has sold more than 3 million, combined all the styles that parents love to hate-- punk, rap and heavy metal--in a rowdy and irreverent set of songs. They had one other quality that helped win white fans for rap: The Beasties are white.