Large projects often consist of multiple source files that include the same header files. The time the compiler takes to process header files over and over again can account for nearly all of the time required to build a project. To make builds faster, LabWindows/CVI 9.0 and later allows users to precompile header files, store the compiled state in a file, and during subsequent compilations, combine the precompiled code with code that is still under development. The first compilation — the one that creates the precompiled header file — takes a bit longer than subsequent compilations, but each subsequent compilation is faster because only modified header files need to be recompiled.
In other words, a pre-compiled header is a cache of header files. The compiler can analyze a set of headers once, compile them, and then have the results ready for any module that needs them.