HP 3000 Manuals

Accessing Files Programmer's Guide

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  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 , 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.)

MPE/iX 5.0 Documentation