There are two main types of CD. The original CDs - CDDA (not CDA as I wrote above) or 'Red Book' CDs - and CD ROMs. CDROMs are computer file systems, like hard disks. CDDAs are not, and don't contain 'files', though operating systems often present the tracks as if they are.

There are also several types of CD which are both - 'extended CDs' - which are not (or shouldn't be) labelled 'Compact Disc Digital Audio' (but sometimes are) and contain both at once, or are non-standard - e.g. they include track names. Some of them used to include deliberate flaws to inhibit copying by computers. Sony famously once included malware on theirs.

Early CD players only played CDDAs. Later ones would play some audio files on CDROMs too. I have some 'extended' CDs which won't play in my older CD players.

I've noticed that most CDs I buy don't say whether they're CDDA - so I assume they're some sort of extended format. What a computer operating system or a media player might make of some of these hybrid CDs could be quite variable. In Linux I can imagine it might start playing the CDDA part under one user - 'nobody' - but not give another user the permission to read the filesystem part. But I'm just guessing.