文档介绍：How pression Works
by Tom Harris
If you download many programs and files off the , you've probably encountered ZIP files
before. pression system is a very handy invention, especially for Web users, because it
lets you reduce the overall number of bits and bytes in a file so it can be transmitted faster over
slower connections, or take up less space on a disk. Once you download the file, your
computer uses a program such as WinZip or Stuffit to expand the file back to its original size. If
everything works correctly, the expanded file is identical to the original file before it was
compressed.
At first glance, this seems very mysterious. How can you reduce the number of bits and bytes and
then add those exact bits and bytes back later? As it turns out, the basic idea behind the process
is fairly straightforward. In this edition of HowStuffWorks, we'll examine this simple method as
we take a very small file through the basic process pression.
Finding Redundancy
Most types puter files are fairly redundant -- they have the same information listed over
and over again. pression programs simply get rid of the redundancy. Instead of listing a
piece of information over and over again, a pression program lists that information once
and then refers back to it whenever it appears in the original program.
As an example, let's look at a type of information