Assembly Language Programming - Fundamentals of Computer Organization and Architecture - page 37

& CHAPTER 3

Assembly Language Programming

In Chapter 2 we introduced the basic concepts and principles involved in the design
of an instruction set of a machine. This chapter considers the issues related to assem-
bly language programming. Although high-level languages and compiler technol-
ogy have witnessed great advances over the years, assembly language remains
necessary in some cases. Programming in assembly can result in machine code
that is much smaller and much faster than that generated by a compiler of a high-
level language. Small and fast code could be critical in some embedded and portable
applications, where resources may be very limited. In such cases, small portions of
the program that may be heavily used can be written in assembly language. For the
reader of this topic, learning assembly languages and writing assembly code can be
extremely helpful in understanding computer organization and architecture.
A computer program can be represented at different levels of abstraction. A pro-
gram could be written in a machine-independent, high-level language such as Java
or C . A computer can execute programs only when they are represented in

machine language specific to its architecture. A machine language program for a
given architecture is a collection of machine instructions represented in binary
form. Programs written at any level higher than the machine language must be trans-
lated to the binary representation before a computer can execute them. An assembly
language program is a symbolic representation of the machine language program.
Machine language is pure binary code, whereas assembly language is a direct map-
ping of the binary code onto a symbolic form that is easier for humans to understand
and manage. Converting the symbolic representation into machine language is per-
formed by a special program called the assembler. An assembler is a program that
accepts a symbolic language program (source) and produces its machine language
equivalent (target). In translating a program into binary code, the assembler will
replace symbolic addresses by numeric addresses, replace symbolic operation
codes by machine operation codes, reserve storage for instructions and data, and
translate constants into machine representation.
The purpose of this chapter is to give the reader a general overview of assembly
language and its programming. It is not meant to be a manual of the assembly
language for any specific architecture. We start the chapter with a discussion of a

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