Chapter 1 Introduction

Almost every kind of organization in our modern society is concerned in some way with information. Corporations keep track of their business dealings, political groups keep lists of potential voters, and families remember whose turn it is to do the dishes. When an organization needs to deal with large amounts of information in an efficient, dependable manner, a computer can be an indispensable aid. This manual describes the MPE/iX file system that is responsible for handling information in the 900 Series of the HP 3000 Family.

Figure 1-1 “File System Interface” shows the relationships among your program, the MPE/iX file system, the MPE/iX I/O System, and the actual hardware of the system. Notice that the MPE/iX file system serves as the interface between you and the rest of the system.

Figure 1-1 File System Interface

The file system is the part of the MPE/iX operating system that manages information being transferred or stored with peripheral devices. It handles various input/output operations, such as the passing of information to and from user processes, compilers, and data management subsystems. Conceptually, these data transfers are very simple: information is arranged into data elements within a record; this record is then input, processed, and output as a single unit. Logically related records are grouped into sets known to the file system as files, which may be kept in any storage medium or sent to any input/output peripheral (as illustrated in Figure 1-2 “Records/Files Relationship”, below).

Figure 1-2 Records/Files Relationship

Since all input/output operations are done through the mechanism of files, you may access very different devices in a standard, consistent way. It does not make much difference to you whether you read your file from a disk or from a magnetic tape, because the file system permits you to treat all files in the same way. This property of the file system gives your program device independence; the name and characteristics assigned to a file when it is defined in a program do not restrict that file to residing on the same device every time the program is run. You, the user, need only reference the file by the file name assigned to it when it was created, and the file system determines the device or disk address where the file is stored and access the file for you. (Of course, you should be aware of the properties of the device you're using. For example, the MPE/iX file system permits you to read a file from a line printer.)