Each alone accessible unit of information in storage is chosen with its numerical memory address. In the modern computers, location-addressable storage generally restrict to primary storage that accessed internally by computer programs, because location-addressability is very efficient, but onerous for humans.
Information is divided into files of variable length, and a particular file is chosen with human-readable file names and directory. The underlying device is yet location-addressable, but the OS of a computer system provides the file system abstraction to make the operation more clear. In modern computers tertiary, secondary and off-line storage use file systems.
Individually accessible unit of information is chosen based on the basis of (part of) the contents stored there. Content-addressable storage may be implemented by using hardware (computer device), software (computer program) with hardware being faster but more expensive option. Hardware content addressable memory is frequently used in a computer's CPU cache.