Editing DLL hell (section)

===Shared in-memory modules===
16-bit versions of Windows (and [[Windows on Windows]]) load only one instance of any given DLL; all applications reference the same in-memory copy, until no applications are using it and it is unloaded from memory. (For 32-bit and 64-bit versions of Windows, inter-process sharing occurs only where different executables load a module from exactly the same directory; the code but not the [[Stack (data structure)|stack]] is shared between processes through a process called "memory mapping".)  Thus, even when the desired DLL is located in a directory where it can be expected to be found, such as in the system directory or the application directory, neither of these instances will be used if another application has started with an incompatible version from a third directory.  This issue can manifest itself as a 16-bit application error that occurs only when applications are started in a specific order.