User`s guide

How Data Is Stored in Files
RT–11 stores data in several different binary codes. These codes are of two major
types:
• Text-file code
• Nontext-file code
Text-File Code
A file that you can read is called a text file, and RT–11 stores the data in that file in
ASCII (American Standard Code for Information Interchange) code. Each character
in this code is represented by seven bits in a byte. The appendix of the PDP–11
MACRO–11 Language Reference Manual for the DEC multinational character set
includes the ASCII character codes. Use the DUMP command to examine a file’s
binary content.
Nontext-File Code
Some files do not contain ASCII characters. These files include the output of
compilers, assemblers, and linkers; and their binary code (that is, the format in
which data is stored) varies.
RT–11 deals with the following nontext-file file types:
• MACRO–11 Assembler Produced Files
— OBJ Files
An object (OBJ) file consists of data and PDP–11 machine language code. It
is used as input to the linker.
• Linker Produced Files
— SAV Files
A memory-image (SAV) file is an executable program file. This file does not
require relocation and can run in a single-job environment, as a background
program under the multi-job monitor including a mapped monitor, as a
foreground virtual job under a mapped monitor, or as a completely virtual
job under a mapped monitor.
— REL Files
A relocatable-image (REL) file is one linked as though its bottom address
were 1000 and with relocation information included in its memory image.
When you call such a program file with the FRUN or SRUN command, the
file is relocated as it is loaded into memory. A relocatable-image file can run
in a foreground environment.
3–10 Using RT–11 Commands