Compact disc
Compact disc (CD) is a digital optical disc data storage format that was co-developed by Philips and Sony and released in 1982. The format was originally developed to store and play only sound recordings (CD-DA) but was later adapted for storage of data (CD-ROM). Several other formats were further derived from these, including write-once audio and data storage (CD-R), rewritable media (CD-RW), Video Compact Disc (VCD), Super Video Compact Disc (SVCD), Photo CD, PictureCD, CD-i, and Enhanced Music CD. The first commercially available audio CD player, the Sony CDP-101, was released October 1982 in Japan.
Mini CD
Most CD players in the late 1980s and early 1990s didn't handle the Mini CD circular indentation and required the use of an adapter, or very careful placement of the CD in the exact middle of the tray. Not until after the major record labels discontinued them, did the CD Players start to have the 80 mm circular indentation as standard.