Files

abstract storage ‘devices’ organised in (typically hierarchical) file system structure

file access:

• sequential (in order) vs. random access (e.g. second, then first, then third block)

file types:

• regular files, dirs, soft links
• special files (e.g. device files, metadata files)

file structure:

• OS’ perspective: files as streams of bytes
• program’s perspective: archives, executables, etc.
• is OS ever aware of the file structure?

file naming:

• different file systems have different limitations/conventions for filenames
• file extensions
• file name length:
  • FAT: 8.3 characters (8 name, 3 extension. later extended to 255)
  • EXT4: 255 characters
• Special chars in filenames:
  • FAT: no “*/:<>?| etc.
  • EXT4: no ‘\0’ and ‘/’ or special names ‘.’ and ‘..’
• case sensitivity depends

file attributes:

• there’s a whole bunch of them

file operations:

• create/delete
• open/close
• read/write
• append
• seek
• get attributes/set attributes
• rename

directories:

• persistent data structures organising and maintaining info about files
• file attrs stored in-band or out-of-band (both commonly used)