This is the third and final volume of a set of reports to describe the theory and construction of the FLAG code. The first volume is devoted to a presentation of the mathematical model to describe a coal gasifier and an explanation of the computational methods used to solve these equations. The second volume is devoted to an explanation of how to use the FLAG code. This final volume provides information on the hardware and system requirements necessary to run the code and details on its internal structure. There is, of course, some overlap in these volumes. Some of the input variable described in Volume II can be understood only through the methodology given in Volume I. In addition, running the code also requires knowledge of JCL, which is part of this volume. Thus, some of the same information is repeated in each of the volumes. Nevertheless, there is a major difference between this volume and the first two volumes. This volume is intended primarily for an individual to bring up the code and make changes to the code. Following the introduction, chapter II provides information concerning the hardware and JCL necessary to implement the code. A number of computer systems are not suitable for FLAG; this is the type of information given in that chapter. Chapter III details the data blocks and variables used throughout the code. This information is most important for modifying the code because it specifies where in the code quantities are created. Chapter IV provides a description of modules and subroutines that make up FLAG. This chapter provides more detail on the actual structure of the code. 2 figures, 91 tables.