DLL hell

DLL hell

Refers to earlier conflicts with Windows DLLs when the wrong one was installed. A Windows DLL is an extension to the operating system that is shared with any application that needs it. Once a DLL is opened, all applications use that single instance. Microsoft always adds features to its DLLs, and in order for an application vendor to ensure that the latest DLL is available, it may install the latest DLL along with its application.

Installation Programs Must Be Smart
If an installation program checks version numbers and never replaces a newer DLL with an older one, there is usually no problem. However, if it replaces a newer DLL with an older one, other applications that depended on the newer DLL may no longer work.

Improvements Were Made
When the DLL concept was developed, computers had little more than 4MB of RAM, and having two instances of the same DLL open at the same time was wasteful of precious memory. However, starting with Windows 2000 and XP, developers could install DLLs in their own application folders, mark them as "not" shared and use them exclusively, never to be replaced. In addition, the newer Windows versions make sure that shared DLLs are not replaced with older versions. See DLL.