Thursday

What is DLL?

1 Comment Jun-07-2007 | Posted by Özgür Özkurt | Printable Version | Level |

If you are using any version of windows, then you are already familiar with this term that I will talk about. However, only a few of those who does not make any programming has detailed information about this file type. In this article, I will share with you about all that I know about DLL(Dinamic Link Library).

It is similar to concept of functions and objects that are used in object oriented programming (OOP) languages. If you are using one operation more than once for a program, then you should make it a function. And you call these functions by using parameters. The logic is same for DLLs. The only difference is that it is stored in a different location than the exe(Executable) file. At this stage, I should explain about the two files that may be executed. First one is EXE file and the second one is DLL. They are stored in binary numerical format and include codes that may be run directly. Let’s return back to the original subject. Let me remind you that you can save from both time and readability if you divide the original program into functions. DLLS also work with the same logic. If you think that dividing the program into sub-functions, then let’s see the other advantages of DLLs:

Advantages of using DLL

A DLL that is written in any of the programming languages can be called from other programming languages by using the appropriate parameters. Assume that you are using a programming language to write your code, but you need an operation that cannot be done by the language that you are using. Then, you can call another DLL that was written in another programming language and use it.

Think that all of these codes are included in one EXE file. You can imagine how much memory a medium sized exe allocates. It is obvious that most of the memory is allocated by the exe file. Every time the program is executed, complete EXE is loaded into the memory and will be executed, and then the result may be a disaster. For this reason, instead of implementing all of the code into an EXE, it is divided into several DLL files. By this way these DLL files are loaded into the memory and used only when they are needed.

Now, think that you have written a big scale program and you have many users. You wrote the program a single EXE (let’s say it is approximately 100Mbyte) and distributed. Then you updated your program. You made the necessary updates and you asked you users to download the whole 100Mbyte file again. I am sure that you will use most of your customers because they will not want to download the whole 100Mbyte once more. However, if you divide the program into several DLL files, it would be enough that you ask your customers to download and replace only the updated DLL files, which means probably only a few Mbytes.

Shortly, we can say that using DLL files make you save speed, time and memory.

Now, let’s look at how MS Windows operation system gets use from DLL files. To do this, it will be enough for you to look at the system32 directory under Windows folder. You will come up against some file names that you are already familiar with. These files include the functions that make the everyday usual routine works that Windows does every day.

Have a nice day.

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