Busing began in 1970 and lasted until 1999, both times as mandated by the courts. At first, schools had to maintain a ratio close to 60% white, 40% nonwhite, which reflected the school system's racial makeup. Magnet schools were introduced in the 1990s. They specialize in a certain area, such as math, IB, foreign language, etc. Students from any area can apply to their program. They were used to attract white students to voluntarily go to schools in black neighborhoods that were a long distance away.
The superintendent/school board haven't come up with a consistent school assignment plan to replace busing. In the last few years I was in school, there was a "choice plan" in which you had a zone of schools you could chose from. You were guaranteed a spot at your "home school", or you could apply for a spot in the lottery to try to get into another school. Now they seem to be using a feeder school system, with some flexibility in it.
Keep in mind, Charlotte-Mecklenburg has over 140 public schools in the system.
Here's a great article about Charlotte and busing:
http://www.slate.com/id/35218/