Mr.LA
Magistrate judge is some sort of associate judge, not the federal district judge himself. Read on. Hope it helps. Why are you asking?
Federal judicial system
In the United States federal court system, "magistrate judges" are appointed by the life-term federal district judges of a particular court, serving terms of eight years if full-time, or four years if part-time, and may be reappointed. Magistrate judges issue warrants, handle lesser criminal cases, arraignments, sentencing, non-death penalty habeas corpus cases, social security appeals, and certain kinds of civil cases. Felonies are typically handled by district judges, as are civil jury trials unless all of the parties to a case agree that the magistrate judge may preside over it. All decisions of a magistrate judge are subject to review and either approval, modification or reversal by a district judge of that court, except in civil cases where the parties consent in advance to allow the magistrate judge to exercise the jurisdiction of the district judge.
Magistrates did not exist in U.S. federal courts until 1968, when the office of "United States commissioner" was restructured and renamed to allow district judges to focus on major cases, with lesser matters handled by magistrates. Magistrates' titles changed again in 1990, when they became "magistrate judges," symbolizing the ever-increasing importance of their work. The system has worked relatively well in the last 30 years, and has tended to shift the Federal courts' caseload to the desired balance. Some legal observers have criticized the increasing powers of magistrate judges, who are neither appointed by the President of the United States nor confirmed by the United States Senate. Nevertheless, with the caseload of the Federal courts increasing steadily, it is likely that magistrate judges will continue to wield considerable authority.
