What is the difference between supervised release and probation?

Supervised release, which has by and large replaced parole, consists of postconfinement monitoring by a sentencing court. A defendant on supervised release must comply with the conditions imposed on him on pain of having his supervised release status revoked and being returned to prison. See Johnson v. United States, 529 U.S. 694, 697, 120 S.Ct. 1795, 146 L.Ed.2d 727 (2000). One inherent difference between supervised release and probation is that in the former a defendant will have served time in prison for his offense, while in the latter he will not have served time. Probation therefore, unlike supervised release, is an alternative to imprisonment. Id. at 711-12 n. 11, 120 S.Ct. 1795.