The IEEE POSIX  group is concerned with standardizing a wide range of operating system services, from basic functionality (1003.1) through networking (1003.12), security (1003.6), and real-time (1003.4). The 1003.4 working group is currently balloting two related standards which will inevitably become international standards – perhaps by the end of 1992. [POSIX.4] is a proposed standard for the support of “applications with real-time requirements”. [POSIX.4a] is the “threads extension” to 1003.1. These two standards offer that which has never before been possible in the fragmented world of real-time – some hope that applications can be written so as to be easily portable from one real-time operating system to the next. The facilities of 1003.4 (POSIX.4) and 1003.4a (POSIX.4a) are already being demanded by large Federal and commercial customers. Support for these standards will become a powerful tool for addressing these markets. What, though, is in these standards? How do they meet the needs of real-time applications? And, equally important, where do they fall short?

ESC_1991_Vol1_Page69_ Gallmeister – Understanding POSIX.4 and POSIX.4A .pdf