It has long been recognized that under the federal Constitution a defendant's plea of guilty to a criminal charge is only valid if it is voluntarily and knowingly made. (See, e.g., Waley v. Johnston (1942) 316 U.S. 101, 104 [86 L.Ed. 1302, 1304, 62 S.Ct. 964].) In June 1969, the United States Supreme Court elaborated on this principle in Boykin v. Alabama (1969) 395 U.S. 238 [23 L.Ed.2d 274, 89 S.Ct. 1709], holding that an appellate court may not presume from a "silent record" that a defendant has voluntarily and intelligently waived the constitutional rights which he implicitly relinquishes by entering a plea of guilty. In Boykin the court invalidated a criminal conviction resulting from a guilty plea in a proceeding in which the record contained no adequate showing of the defendant's waiver of his rights.
