The 1980s really began in 1978 with the release of Van Halen I, but ended in 1991 with the release of Nevermind.
The 90s began in 1991 with Nevermind and ended in 1999, with the launch of MSN Messenger.
MSN signaled the beginning of the internet age: of course this means Napster, but it also means a new way of gaining status through music via membership with online groups.
Before MSN and the internet, status was in radio plays and album purchases. After MSN, people shared what they were listening to as their MSN statuses, their various online profile pages, and the CDs they ripped their pirated music onto. This lead to unprecedented diversity in popular musical genres: RnB (Usher), rap (DMX and Jay Z), emo (MCR and FOB), and nu metal (Limp Bizkit). Consequently, physical music sales peaked in 1999.
The 2000s ended in 2008 with the launch of iTunes, and the focus on digital singles and the shunning of music videos. All music had rap verse as well.
The 2020s started in 2016, with the rise of Soundcloud rappers and musciains. We are still in that era.