To expand on what Tom wrote, most film composers write a "short score," or "sketch," from which the orchestrator works to prepare a full score (one staff for each group of instruments). From it a copyist will prepare separate parts for each instrument. A copyist will also usually prepare a very clean copy of the composer's sketch, referred to as a "piano/conductor score" to be used for studio files and copyright deposits, and they have been used to conduct the orchestra during the recording session. Prior to the age of xerography these were done on hectograph or mimeograph stencil. The examples in the PMS Ben-Hur articles were piano/conductor scores.