The key in a file system attribute dictionary whose value indicates the amount of free space on the file system.
The corresponding value is an NSNumber object that specifies the amount of free space on the file system in bytes. The value is determined by statfs().
Available in Mac OS X v10.0 and later.
Declaration Syntax Version Information- Available in Monobjc Bridge: 10.6 (For Mac OS X 10.6 and later), 10.5 (For Mac OS X 10.5 and later)