The Gem was introduced in 1899. This model D dates from about 1908. This combination machine has a model K reproducer that can be alternated to play both two and four-minute recordings on phonograph cylinders. It originally sold for around $15. Phonograph cylinders are the earliest commercial medium for recording and reproducing sound. Commonly known simply as "records" in their era of greatest popularity (c. 1896–1915), these hollow cylindrical objects have an audio recording engraved on wax on the outside surface, which can be reproduced when they are played on a mechanical cylinder phonograph. In the 1910s, the competing disc record system triumphed in the marketplace to become the dominant commercial audio medium.