Since an expansion card such as a video adapter, hard drive controller, or network adapter could use allocations of memory in many of the upper memory areas, configuration of some combinations of cards required careful reading of documentation, or experimentation, to find card settings and memory mappings that worked.
22.
This approach eliminates conflicts by allowing applications to load unique versions of a module into their address space, while preserving the primary benefit of sharing DLLs between applications ( i . e . reducing memory use ) by using memory mapping techniques to share common code between different processes that do still use the same module.
23.
The function mmap ( ), which creates a mapping of a file given a file descriptor, starting location in the file, and a length, is part of the POSIX specification, so the wide variety of POSIX-compliant systems, such as UNIX, Linux, Mac OS X or OpenVMS, support a common mechanism for memory mapping files.
