IBM 1620 User Manual

The FORTRAN System
The Processor
The Source Program
The Ob;ect Program
Instruction # 38 - subtract the number stored at location 00639 from the
result in 00879.
Instruction #39 - store the result of the two additions and the one sub-
traction at location 01479.
The same program, coded in FORTRAN, might be:
D=A+X-Y
The complete solution of a problem, depending upon the type of problem
to be solved, may require hundreds or even thousands of instructions. The com-
puter can refer to them one after another, or it can be instructed to repeat,
modify, or skip over certain instructions,
depending on intermediate results or
circumstances. However, such circumstances must be anticipated and appropriate
instructions included in the program.
The ability to repeat operations combined with the ability to modify and
skip over instructions permits a significant reduction in the number of instruc-
tions
required to perform any given job.
The decision-making ability of the computer enables it to handle exceptions
to
standard procedures. Since a system will "remember" instructions for dealing
with the exceptions, it can be made to handle automatically any situation that
develops.
Up to this point, the computer has been treated as though it were a sepa-
rate piece of equipment to be used by itself. However, in actual practice, the
computer is used in conjunction with other equipment and with programming
systems that are designed to aid the programmer in the preparation and opera-
tion of his programs. 1hese total facilities for receiving information and produc-
ing desired results are called a data processing system. One part of such a system
may be FORTRAN which is a programming system that enables a programmer to
write a
program with less effort than would otherwise be required. For the
purpose of explanation, FORTRAN will be described in two parts: the FORTRAN
System and the FORTRAN Language.
The FORTRAN System consists of the following parts.
The processor is a program developed by IBM. Its purpose is to tell the computer
how to translate the FORTRAN language, written by the programmer, into the
machine language used by the computer.
The source program defines the ultimate operations the computer is to perform
and is written by the programmer in the FORTRAN language.
The source program, then, is input to the computer along with the FORTRAN
processor. The computer follows instructions from the processor to convert the
source program into a machine language which can then be run on the com-
puter. This machine language program is called the object program. When the
object program and the data to be processed is run on the computer to cause the
desired computations, it is said to be executed. That is, execution is the actual
operation of
the computer while it is under the direction of the object program.
It is important in learning FORTRAN to remember the difference between the
processor and the source program. The operation of converting the source pro-
gram to an object program is referred to throughout this manual as compilation,
Introduction to IBM FORTRAN 7

IBM 1620 Specifications

General

Category	Desktop
Manufacturer	IBM
Model	1620
Introduced	1959
Weight	Approximately 1, 000 pounds
Memory	20, 000 to 60, 000 digits
Programming	FORTRAN, Symbolic Programming System (SPS)
CPU	Decimal, variable word length
Storage	Magnetic disk drive (IBM 1311)

Summary

Introduction to IBM FORTRAN

Writing the 1620 FORTRAN Program

Floating Point Arithmetic Explained

Details floating point arithmetic, mantissa, and exponent representation.

FORTRAN Constants: Definition and Types

Defines constants and explains fixed and floating point constant formats.

FORTRAN Variables: Definition and Naming

Explains variables, their distinction from constants, and naming conventions.

FORTRAN Subscripts and Arrays

Explains subscripts for referencing array elements and defining arrays.

Arithmetic Statements

Describes how numerical calculations are defined using arithmetic statements.

FORTRAN Expressions: Structure and Operations

Defines expressions and lists the basic FORTRAN operation symbols.

Control Statements

Explains control statements that provide flexibility in program development.

Unconditional GO TO Statement

Describes the unconditional GO TO statement for transferring program execution.

Computed GO TO Statement

Explains the computed GO TO statement for conditional transfers.

IF Statement for Conditional Logic

Details the IF statement for transferring program flow based on expression values.

DO Statement for Looping Constructs

Explains the DO statement for simplifying loop programming and providing flexibility.

Nested DO Statements and Rules

Explains the rules for nesting DO statements within other DO statements.

Input/Output Statements

Explains statements used to read data into programs and output results.

READ Statement for Card Input

Details the READ statement for inputting data from punched cards.

ACCEPT Statement for Typewriter Input

ACCEPT TAPE Statement for Paper Tape Input

PUNCH Statement for Card Output

TYPE Statement for Typewriter Output

PRINT Statement for Printer Output

Explains the PRINT statement for outputting data to the 1443 Printer.

PUNCH TAPE Statement for Paper Tape Output

FORTRAN Specification Statements

Introduces specification statements, including FORMAT and DIMENSION.

FORMAT Statement for Data Conversion

Explains the FORMAT statement for controlling input/output data conversion.

FORMAT Statement Output Specifications

Explains I (Integer) and F (Floating Point) conversion for output.

Specifying Alphameric Fields in FORMAT

DIMENSION Statement

Explains the DIMENSION statement for allocating storage for arrays.

Writing FORTRAN Statements for Problem Solution

Processing with the FORTRAN Pre-Compiler

Operating Principles

Producing the Object Program

Explains the fundamental steps for creating the object program from source code.

Clearing Core Storage to Zero

Console Switch Settings for Compilation

Loading the FORTRAN Compiler

Explains the procedures for loading the compiler program deck or tape.

Compiling the FORTRAN Source Program

Describes how to initiate compilation of the FORTRAN source program.

Loading FORTRAN Subroutines

Explains how to load subroutine decks or tapes after source program compilation.

Common Source Program Errors During Compilation

Executing the Object Program

Details the procedures for loading and executing the compiled FORTRAN object program.

Inputting Data from the Keyboard During Execution

Using the Trace Feature for Debugging

Explains how to use the trace feature to monitor program flow and check correctness.

Analysis of the FORTRAN Program

FORTRAN Subroutines: Overview and Classification

Introduces FORTRAN subroutines, their types, and available sets.

Floating Point Accumulator (FAC)

FORTRAN Subroutine Linkage Mechanism

Error Analysis of FORTRAN Subroutines

Discusses errors, their codes, and FAC values for FORTRAN subroutines.

FORTRAN Subroutine Error Checks and Codes

Lists subroutine error checks, error codes, and FAC values for error conditions.

Adding Custom Subroutines to FORTRAN

Processor

Processor Subroutine Management

Storage Allocation

Storage Allocation After Compiler Loading

Storage Allocation After Source Program Processing

The FORTRAN Pre-Compiler Program

Operation of the FORTRAN Pre-Compiler

Explains the two-phase operation: Error Analysis and Final Program Summary.

Pre-Compiler Error Code Categories

Categorizes the common errors detected by the Pre-Compiler program.

FORTRAN Statement Number Errors

FORTRAN Transfer Statement Errors

General FORTRAN Statement Errors

Error Analysis Phase

Restart Procedures in Error Analysis

Final Program Summary in Pre-Compiler

Program Switch Settings

Loading the FORTRAN Pre-Compiler Program

Details the steps required to load the FORTRAN Pre-Compiler program.

Processing the Source Program with Pre-Compiler

Explains how to process the source program using the Pre-Compiler.

Pre-Compiler Program Deck Structure

Pre-Compiler Program Tape Structure

Pre-Compiler Tape Data Identification

Duplicating the FORTRAN Pre-Compiler Tape

Appendix A - Summary of 1620 FORTRAN Statements

ACCEPT Statement Summary

ACCEPT TAPE Statement Summary

DIMENSION Statement Summary

Summarizes the DIMENSION statement for array declaration.

DO Statement Summary

Summarizes the DO statement for loop control.

FORMAT Statement Summary

Summarizes the FORMAT statement for data conversion.

GO TO Statement Summary

Computed GO TO Statement Summary

IF Statement Summary

Summarizes the IF statement for conditional logic.

PRINT Statement Summary

Summarizes the PRINT statement for printer output.

PUNCH Statement Summary

PUNCH TAPE Statement Summary

READ Statement Summary

Summarizes the READ statement for card input.

TYPE Statement Summary

Summary of 1620 Operating Principles

1620 Typewriter Input Operations

Manual Data Entry via Typewriter

Typewriter Output Operations

Paper Tape Input Procedures

IBM Tape Punch Operation

IBM 1621 Paper Tape Reader Operation

Card Input

Covers the process of inputting data via punched cards.

IBM 1622 Card Read Punch Overview

Provides an overview of the IBM 1622 Card Read Punch.

1622 Card Feed Motor Control

1622 Card Read Operation

1622 Card Punch Operation

1622 Operator Keys and Lights

1622 Card Reader Controls and Indicators

1622 Card Punch Controls and Indicators

IBM 1443 Printer Overview

Provides an overview of the IBM 1443 printer.

1443 Printer Keys, Lights, and Switches

Details the keys, lights, and switches for operating the 1443 printer.

1443 Printer Start Key Operation

Explains the operation of the 1443 printer's start key.

1443 Printer Stop Key Operation

Details the operation of the 1443 printer's stop key.

1443 Printer Power On Light

1443 Printer Ready Light

Explains the function of the 1443 printer's ready light.

1443 Printer Sync Check Light

Describes the 1443 printer's sync check light and error conditions.

1443 Printer Parity Check Light

Explains the 1443 printer's parity check light indicator.

1443 Printer Form Check Light

1443 Printer End-of-Form Light

1443 Printer Manual Controls

Details the manual controls for operating the 1443 printer.

1443 Character-Set Selection Switch