What is a .dll file?

Answer 1

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A DLL is a library that contains code and data that can be used by more than one program at the same time. For example, in Windows operating systems, the Comdlg32 DLL performs common dialog box related functions. Therefore, each program can use the functionality that is contained in this DLL to implement an Open dialog box. This helps promote code reuse and efficient memory usage.

By using a DLL, a program can be modularized into separate components. For example, an accounting program may be sold by module. Each module can be loaded into the main program at run time if that module is installed. Because the modules are separate, the load time of the program is faster, and a module is only loaded when that functionality is requested.

Additionally, updates are easier to apply to each module without affecting other parts of the program. For example, you may have a payroll program, and the tax rates change each year. When these changes are isolated to a DLL, you can apply an update without needing to build or install the whole program again.

The following list describes some of the files that are implemented as DLLs in Windows operating systems:

* ActiveX Controls (.ocx) files

An example of an ActiveX control is a calendar control that lets you select a date from a calendar.

* Control Panel (.cpl) files

An example of a .cpl file is an item that is located in Control Panel. Each item is a specialized DLL.

* Device driver (.drv) files

An example of a device driver is a printer driver that controls the printing to a printer.

DLL stands for "Dynamic Link Library". A dll is a file that contains programming code modules that more than one program may need to access. By linking to the dll, other programs can use the code withought having to include it in their own files, which saves space. Also, updating the dll effectively updates the progams using it without having to re-write or modify each individual program.

In some cases dlls can be run as programs, and some dlls are malware or spyware.

dlls are usually found in the windows sub directory and the windows\system or \system32 subdirectorys. When a program or game is installed in the ProgramFiles (or other) subdirectory their dll files may be installed in that directory as well.

A program consists of a series of instructions written in a computer language like C, C++, Java etc which the computers read and then execute. Computers are dumb machines, to get a job done using a program the programmer needs to include a detailed series of instructions to the computer in the program. An example would be: To add two numbers, one would need to instruct the computer to fetch those two numbers from two different memory locations where they are stored, add them and then store the output somewhere safe back in the memory. ie, to add two numbers one would need to write a series of instructions in the program. Imagine the situation if you have to add numbers more than a few times throughout the program? Well, programmers soon found a way out. They aggregated the frequently used series of instructions into a sub-program which could be called anytime when needed from the main program. These are popularly known as 'Functions' in C, C++ terms (different languages have different names for such entities). A group of related 'Functions' (like add, subtract, multiply ..) are further aggregated and placed in a separate and independent file called a library and came with a .lib extension. Earlier Programs were 'Statically' linked to the library, which means that when the final program is built, the instructions from the library will get copied to the main program. This is okay as long as the program is not very big, but dampens performance and slows the computer if the program is big.

So programmers came up with the idea of 'Dynamically' linking a library. ie, the main program and the library would be kept as two separate programs and when the main program wanted a function in the library it would 'Dynamically' call the function in the library while the main program is still running. This scheme also offered another advantage; multiple, separate programs could use a single copy of the library thereby saving up on computational resource.

A well known software company from Redmont supplies such libraries in a file with a .dll extension, and hence dynamically linked libraries are also called DLLs.

Different operating systems have different preferences as to where the libraries should be stored. In MS Windows you will find them in the C:\...\system\ or C:\...\system32\ folder.

Cheers... JPlacid

A DLL is a Dynamic Link Library A dynamic link library (DLL) is a collection of small programs, which can be called upon when needed by the executable program (EXE) that is running. The DLL lets the executable communicate with a specific device such as a printer or may contain source code to do particular functions.