POSIX is a family of standards specified to maintain portability between operating systems.
It defines the API along with the command line shells and utility interfaces for software compatibility.
After unix was selected by general consensus as the standard system interface because its manufacturer neutral, there was a need to develop a common denominator Especially in light of an increasing number of unix systems.
mmap is a POSIX compliant UNIX syscall that maps files or devices into memory. It is a method of memory-mapped file I/O.
Implements demand paging, because file contents are not read from disk directly and initially do not use physical RAM at all.
Actual reads are performed in a “lazy” manner after a specific location is accessed.