Learn in the textbookOptical Disc Storage Media — CD, DVD, Blu-ray
DefinitionA CD-R is a write-once CD on which the user can write data only once into a dye-based recording layer (記録層).
ExplanationWhen the drive fires a stronger laser beam, the heat alters the dye and changes how it reflects light, and that change is the recording. The altered spots cannot be restored, so anything written can be neither erased nor overwritten. As long as unwritten space remains, more data can be added there later.
AnalogyLike a farewell card signed in permanent marker: you can add messages in the blank space, but what is written stays.
Memory hookThe R stands for Recordable, marking it as a CD that users can record on themselves.