to store data in externally connected storage media such as ROM cartridges, floppy disks, memory cards and USB flash drives. Floppy disks and cartridges were obsolete by the early 2000s, with memory cards starting to replace them shortly afterwards. USB storage was originally less common at the time, but was later popularized by Yamaha's lineup of workstation keyboards in 2005 and has become a standard feature ever since. Most keyboards since the 2010s use USB storage, with the exception of some Casio and Korg models. Music stand: A metal or plastic rack for holding sheet music or music books upright. The music stand is usually removable to facilitate storage and transportation. Sustain jack: If a home keyboard has a sustain feature, replicating the device used on acoustic pianos, only a 1/4" jack is provided. The musician must buy a separate sustain pedal and plug it in. By comparison, on a digital piano, a sustain pedal is often built into the frame. The least expensive home keyboards do not have a sustain function or a sustain pedal jack, which limits their use to early beginners. History Classifications Conventional home keyboards differ from other electronic keyboards due to the design, features and target market: Digital piano - Electronic keyboards designed to sound and feel like an ordinary acoustic piano. They typically contain an amplifier and loudspeakers built into the instrument. In most cases they can fully replace acoustic pianos and provide several features, such as recording and saving files to a computer. Many digital pianos can imitate the sounds of several instruments, including a grand piano, electric piano, pipe organ, Hammond organ and harpsichord. They are not sensitive to the climate or humidity changes in a room and there is also no need for tuning, as with acoustic pianos. Digital pianos are often mounted on stands with a fixed sustain (or other) pedal attached to the frame; as such, most are not designed for transportation. The target market is mid-level to advanced pianists. Stage piano - A type of high-quality digital piano with weighted keys, designed for professional touring use on stage or in a recording studio. The Hammond organ and electric piano sounds on a stage piano are typically more realistic than those found on a digital piano. Synthesizer - Electronic keyboards that use various sound synthesis technologies to produce a wide variety of electronic sounds. Workstation - Professional electronic keyboards