Summary

In this chapter, we provided a schematic of the multiple software layers involved in data input and output. Programmers at the assembly language level, and sometimes at higher levels of programming languages, can choose one or more of the layers of software routines for I/O implemented by a given programming environment and operating system. The higher layers may offer abstraction and some device-independence, but may not afford access to all of the actual capabilities provided by the lower layers of software and, ultimately, by the underlying physical layers. (The writers of fast-paced PC games know this, and exploit the lower levels of I/O implementation.)

We elected to discuss some of the I/O functions of the C language, as they can be called in analogous ways from an Itanium assembly language program in either HP-UX or Linux programming environments. We have shown the details of argument passing between such functions and four sample calling programs. These programs have illustrated, in various combinations, I/O from and to the keyboard and display, I/O from and to ASCII text files, a bubble sort for string data, and a bubble sort for integer quantities. We omitted system-dependent aspects of error detection and recovery, as they are outside the scope of Itanium architecture.