There are some things however you may want to stay away from in purchasing a digital piano. Here some examples:
The Roland KR105 ensemble piano, the Kawai CP207 ensemble grand piano, and others like it still have a floppy disk drive built in to the piano. Those things are old technology and very outdated now. They used to be on computers not so long ago (remember?). Now when it comes to digital memory storage, pianos use USB flash drives, SD cards, or even DVD's (which are getting somewhat outdated as well). A digital piano with a floppy disk drive in it shows its age and because of that, depreciates even more regardless of what else that piano may do. So try to avoid new pianos with floppy disk drives in them. Also, beware of low "polyphony." If at all possible, make sure your piano is at least 96-note polyphonic because it enables you to play the built-in sounds properly. It would be like buying a computer that has a low amount of RAM or a small 20-gig hard drive; you wouldn't want to do that. And also it would help if the piano had a USB output on it to connect to computers easily should you ever want to interact with computer music software.
If you are buying a recent used digital piano for a good low price, and it has older features on it such as a floppy disk drive or low polyphony, that is probably fine as long as you understand its limitations and how it could affect your playing.
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