As the process of music-by-computer becomes more and more common, the accurate and rapid input of music is increasing in importance. In the case of Western music, the technology of musical composition and the automatic recognition of musical notes by computer began in the late 1960s and has matured in various ways, such as auto-recognition and conversion of the musical note using MIDI (Musical Instrument Digital Interface) and other formats. However, a straightforward input/output system for Korean classical music into Jeongganbo, the Korean traditional musical format, doesn't yet exist. Therefore, in this paper, we review the structure of Jeongganbo (which has been used since the era of King Sejong the Great) and lay out the design of a computer-based input/output system for Jeongganbo. Also, for ease of input, we offer a graphical user interface. With an input/output system defined, it is possible to manage Korean classical music systematically, to build a digital database of Jeongganbo, and to search that database rapidly. Upon digitization of Jeongganbo, it becomes much easier to convert Korean musical notes into Western-style musical notes, to convert Jeongganbo using MIDI, and to compose Korean classical music.