Introducing a New Open Systems Environment

What's POSIX?

POSIX is an acronym for Portable Operating System Interface. The POSIX standard, IEEE Std 1003.1-1990, is an international standard that defines common interfaces as a basis for open systems. IEEE POSIX 1003 is actually a group of standards, each of which addresses a specific area of system technology. The POSIX standards describe functions of an operating system interface that applications must use if they are to be "POSIX compliant." Systems that implement the standard functions are said to be POSIX compliant.

Initially, MPE/iX is implementing two of the standards to maximize the software portability of applications: C language application programming interfaces (also called POSIX.1) and a command interpreter (shell) and utilities (called POSIX.2).

The main reason for implementing POSIX.1 functions on a system is to increase software portability and minimize porting costs. Since POSIX.1 is based on Berkeley Software Distribution and AT&T's System V Interface Definition, UNIX applications can be ported more easily to HP 3000 computer systems. Applications developed on any POSIX-compliant system using POSIX.1 functions can be ported to other POSIX-compliant systems and run with little or no modification.

The initial implementation of POSIX.1 makes MPE/iX POSIX compatible. That is, it supports most of the key POSIX features including the hierarchical directory structure, long file names, and process signals. (Signals notify processes of events that occur on the system, such as hardware exceptions.)

POSIX.1 defines procedural interfaces for C programs to high-level, basic operating system services. These services include creating and purging directories and files; creating, controlling, and terminating processes; interprocess communications (for example, signals); byte- stream files; user identification; grouping users for file sharing purposes; defining and altering file security; grouping processes for signal sharing; and changing a user's location within the file system.

How does POSIX change MPE/iX?

In implementing the 1003.1 and 1003.2 functions, HP has enhanced the MPE/iX operating system. The main changes include

These enhancements expand the current MPE file system structure. For example, prior to Release 4.5 and 5.0, the file system allowed you to create files under a group. As of Release 4.5 and 5.0, you can create HFS directories, as well as files, under groups, or accounts.

MPE has traditionally imposed constraints on naming syntax. Names could not exceed eight characters in length and could not contain special characters. MPE/iX now provides an expanded naming syntax, called HFS syntax, that allows for longer file names and has fewer constraints. HFS syntax is available for use in addition to the traditional MPE syntax.

What does POSIX offer you?

MPE/iX enhancements enable you to do the following:

When MPE/iX Release 4.5 and 5.0 is installed, you automatically have access to POSIX functionality. No additional configuration is required for you to use many of the POSIX features described in this document.

If you are a general user on MPE/iX, your activities need not change. You can use the new features such as creating and using directories within groups accessible to you.

If you are a programmer, standard programmatic and interactive interfaces provide a standard development environment enabling source-sharing across platforms. This development environment allows you to implement open systems environment features.

If you are a system administrator, MPE/iX enables you to manage the system basically the same as you have for MPE/V or MPE XL.

Programmers using the MPE/iX system may want to use the MPE/iX Developer's Kit (36430A) to port open system applications onto MPE/iX. In this case, system administrators need to be aware of programming activities so that they can support them when managing the MPE/iX system.

Postponing the use of POSIX features

The introduction of POSIX features on MPE/iX places new demands on system managers. Today, system managers have a full workload without extra time to learn the new POSIX concepts. Chapter 3 discusses options available to those of you who may wish to postpone using POSIX features.