A Red Book Audio CD (CD-A) contains only a single audio stream in the 44.1kHz 16-bit format, divided into tracks using markers. It does not have a file system, meaning there are never actual files (neither AIFF nor WAV) on a CD-A.

The automatic mounting of a CD-A as a virtual file system is a macOS-specific feature. This makes the tracks appear as AIFF “files,” even though they do not physically exist on the CD. When copied to a Mac’s hard drive, the operating system adds the necessary headers, creating a new AIFF file containing the track’s audio data.

On Windows, the system instead displays .cda “files,” which similarly serve as references rather than actual audio files.