Page 16 - DCAP507_SYSTEM_SOFTWARE

System Software

Notes 1.3.3 Loader
Loader is a custom that loads an object program and organizes it for execution.
In a computer operating system, a loader is a constituent that positions a specified program
(which can be an application or, in some cases, part of the operating system itself) in offline
storage (like a hard disk), loads it into main storage (in a personal computer, it's known as
random access memory), and provides that program control of the computer (permits it to
execute its instructions).
A program that is loaded may itself enclose components that are not primarily loaded into main
storage, but can be loaded if and when their logic is required. In a multitasking operating
system, a program that is at times called a dispatcher organizes the computer processor's time
between different tasks and calls the loader when a program related with a task is not already in
main storage.

1.3.4 Linker
Linking is the process of binding an exterior reference to the accurate link time address. An
external reference is said to be uncertain until linking is performed for it. It is said to be resolved
when its linking is accomplished.

1.3.5 Macros

A macro displays a generally used group of statements in the source programming language.
The macro processor substitutes every macro instruction with the equivalent group of source
language statements. This is known as expanding the macros.
Macro instructions permit the programmer to write a shorthand edition of a program, and
leave the mechanical details to be managed by the macro processor.

Example: Presume that it is required to save the contents of all registers before calling a
subprogram.

Did u know? The most common utilization of macro processors is in assembler language
programming.

However, macro processors can also be used with high-level programming languages, operating
system command languages, etc. A macro call is abbreviation (or name) for several code. A
macro definition is a succession of code that has a name (macro call). A macro processor is a
program that replaces and specializes macro definitions for macro call.

Task Define macro instruction.

Self Assessment

Fill in the blanks:
11. .................................... is the most significant system program that performs as an interface
among the users and the system.

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