Definition: An archive is a collection of
files and/or directories stored together in one file.
Purpose: An archive is used to conserve disk
space.
Archives do not have to be compressed. An example of a
non-compressed archive is a tape backup or tar archive. However,
most archives are compressed in some manner.
Archives may consist of multiple files of different types. Any
file type can be placed in an archive, including, but not limited
to, applications and data files.
Archives may consist of directories of files &
subdirectories.
Decompression usually restores the original directory structure.
Commonly the compressed directory structure is restored to a
user-controlled location.
The size of a compressed archive may exceed disk storage.
Many archives are very large (> 2MB) and therefore cannot fit
on a single floppy disk. Such archives require a spanning or
splitter utility.
Automatic hard drive compression.
Drive Space, Stacker - Operating System level compression which
compresses files when not in use. When a file is requested, it is
automatically decompressed.
Data/Executable (binary) Files vs.
Graphic/Image Files
Lossless Algorithms are used for compressing Data/Executable
(binary) Files.
Lossless Algorithms result in the decompressed file being
identical to the original compressed file.
Lossy Algorithms are used for compressing Graphic/Image Files.
Lossy Algorithms result in the decompressed file NOT being
identical to the original compressed file.
The compression algorithms take advantage of the
limitations in the human vision system.
Some compressed graphic file formats use lossless
algorithms.
Binary files can not be compressed in a lossy manner
because the exact information must be stored.
