What are these "zipped" and "self-extracting" archives, anyway?

ZIP FILES:

Files with the extension .ZIP are "compressed" or "archived"
collections, often consisting of several files.  "ZIPPING" is a way of 
packing several large files within a single "ZIP" file that is often
much smaller than the original files.  Therefore, they are easier and
faster to transport.

Several utilities are widely available to "ZIP" or "UNZIP" files, among
them:

PKZIP     by PKWARE ( http://www.asizip.com/dosinfo.htm )
PKUNZIP   by PKWARE (same source)
PAK       by Nogate Consulting
UNZIP     by Samuel Smith
REARJ     by Robert Jung
LHA       by Haruyasu Yoshizaki
ICE       by Haruyasu Yoshizaki
WINZIP    by Nico Mak Computing ( http://www.winzip.com ) 

To "unzip" a file using a DOS archive utility, one types 
the utility name followed by the name of the archived file:
For example:   PKUNZIP BOOKLIST  (extension .ZIP is assumed) 
The "BOOKLIST.ZIP" file will then expand from its "zipped" size 
of about 300K to an unzipped database file almost 1.8MB in size.


SELF-EXTRACTING ARCHIVES:

It is possible to convert a "ZIP" file to a "self-extracting archive" 
which can be "unzipped" without the use of an external tool such as 
PKUNZIP.  Such files carry the extension .EXE, like any executable file. 
To "unzip" or "unpack"  such files, one merely types the filename.  
For instance, to unzip the BOOKLIST.EXE archive, one types "BOOKLIST" 
at the DOS prompt or executes "BOOKLIST" from WINDOWS.

In either case, it is a good idea to unzip files in a separate 
directory, because sometimes the result can be a large number of 
files that can intermix with other filesnames in a directory and 
be difficult to find.