In 1964 the United States Copyright Office began to register software as a form of literary expression. The office based its decision on White-Smith Music Co. v. Apollo , where the Supreme Court determined that a piano roll used in a player piano did not infringe upon copyrighted music because the roll was part of a mechanical device. Since a computer program is textual, like a book, yet also mechanical, like the piano roll in White-Smith, the Copyright Office granted copyright protection under the rule of doubt. In 1974, Congress created the Natural Commission on New Technological Uses (CONTU) to investigate whether the evolving computer technology field outpaced the existing copyright laws and also to determine the extent of copyright protection for computer programs. CONTU concluded that while copyright protection should extend beyond the literal source code of a computer program, evolving case law should determine the extent of protection. The commission also felt copyright was the best alternative among existing intellectual property protective mechanisms, and CONTU rejected trade secret and patents as viable protective mechanisms. The CONTU report resulted in the 1980 Computer Software Act, and the report acts as informal legislative history to aid the courts in interpreting the Act. In 1980 The Copyright Act was amended to explicitly include computer programs. Title 17 to the United States Code states that it is illegal to make or to distribute copies of copyrighted material without authorization, except for the user's right to make a single backup copy for archival purposes. Any written material (including computer programs) fixed in a tangible form (written somewhere i.e. printout) is considered copyrighted without any additional action on the part of the author. Therefore, it is not necessary that a copy of the software program be deposited with the Copyright Office in Washington, D.