ROMlib is ARDI's implementation of approximately 1,200 Classic
Macintosh OS routines. The choice of routines to be included in ROMlib
was based both on the order in which routines were added to Mac OS by
Apple and examination of popular programs to see which routines they
depended on. ROMlib is the heart of both Executor
and Carbonless Copies.
ROMlib routines have to reproduce the exact behavior of their
corresponding Mac OS routines. Macintosh applications rely
on the layout of data structures whether the data structure is documented
or not. Macintosh applications also "patch out" routines by replacing
a Mac OS (or ROMlib) routine with their own implementation. Such patching
imposes even more compatibility restraints.