Intermec 6100 Reference Guide

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Look in the Windows System directory on your PC, and you will find many files

with the extension DLL.  These are dynamic link libraries.  These are nothing

more than subroutines.

In computer programming, subroutines are subsets of computer code separated

from the main program, so that the subset can be reused many times by differĆ

ent parts of the program.  The word dynamic describes the key difference beĆ

tween the DOS subroutines and the Windows DLLs.  The dynamic aspect of a

DLL means that the DLL is loaded into execution memory only when it is needĆ

ed and is removed when its job is done.  DOS subroutines are bound to the DOS

application program.  If two programs on a DOS PC use the same subroutine,

each of the DOS programs contains its own copy of the subroutine.  The DOS

program subroutine is always present in executable memory even if it is not

needed at any given time.
Any application that conforms to the API of a specific DLL may use the DLL,

and avoid duplicating the logic within its own application.  One of the most wideĆ

ly used DLLs is COMMDLG.DLL, which is supplied with Windows.  This subrouĆ

tine library provides many common Windows dialog boxes.  Have you ever noĆ

ticed that the File Open dialog box looks the same across many of your Windows

applications?  This common look occurs because the dialog is invoked through a

call to COMMDLG.DLL.  The application itself does not even have a File Open

dialog!  Giving the Windows applications a consistent look and feel, is one of the

key benefits of these shared subroutine libraries.