Back in the 90s it was common for databases to implement their own file systems or memory management Informix in the mid/late 1980s initially had Shared Memory

Back in the 90s it was common for databases to implement their own file systems or memory management Informix in the mid/late 1980s initially had Shared Memory implementations in UNIX platforms that supported it. Then, the Turbo/OnLine/IDS servers added the option of raw disk partition use for database spaces to avoid filesystems altogether (and do raw unbuffered I/O).