Virtual File System. It's the abstraction layer between the user an real file systems like ext2, minix and msdos. Among other things, i job is to flush the read buffer when it detects a disk change on th floppy disk drive:
What’s the purpose / use of primary and foreign keys?
Primary and foreign keys are a way in which to constrain related data together to ensure data in your database remains consistent and to ensure no redundant data is in the database as a result of ...