Linker and Loader Explained

Compiler,Interpreter,Linker,Loader

Regardless of what language you use, you
eventually need to convert your program
into a language that the computer can
understand
Two ways for doing that:
compile the program or
interpret the program

A compiler is a computer program that translates a
program in a source language into an equivalent program
in a target language.
or
Compilers: Translate a source (human-writable) program
to an executable (machine-readable) program
Source code Compiler Executable
Input data Executable Output data

Translate the entire program.
Convert the entire program to machine code, when
the syntax errors are removed then converted into the
object code
Requires more main memory
Neither source nor the compiler are required for
execution.
Slow for debugging and testing.
Execution time is less.
Security of source code .

Interpreter is a program that executes instructions written
in a high-level language
or
Interpreters: Convert a source program and execute it at
the same time.
Source code
Input data
Output dataInterpreter

Translate the program line by line.
 each time the program is executed ,every line is
checked for syntax error & then converted to
equivalent machine code directly.
Requires less main memory
Source program and the interpreter are required for
execution.
Good for fast debugging and testing.
Execution time is more.
 No Security of source code .

Source
File
Source
File
Source
File
Compiler
(Assembler)
Compiler
(Assembler)
Compiler
(Assembler)
Object Code
File
Object Code
File
Object Code
File
LINKER
Object Code
File
Object Code
File
Object Code
File
LOADER
Main Memory
Executable File / Load
Module
Execution
Object Code
Libraries

A program that takes as input the object
files of one or more separately compiled
program modules, and links them together
into a complete executable program,
resolving reference from one module to
another.

A program that takes an input an executable
program, loads it into main memory, and causes
execution to being by loading the correct starting
address into the computer register.
When the program finished, control must
somehow be returned to the operating system.

A single object file might contain machine code
for only one procedure or a set of procedures.
An executable file must contain all the machine
code needed for a particular program; it must
contain the address of the first instruction to be
executed.

I. Absolute loader: absolute loader is a primitive type
of loader which does only the loading function. It
does not perform linking and program relocation.
II. Bootstrap loader: when the computer is turned on
absolute loader is executed. this loader is responsible
for loading the operating system and transferring
control to it. This loader is present in the ROM area
of main memory.
III. Relocateabel loader: this loader is responsible for
relocation and loading.

I. Linking loader: this linker performs all the linking and
relocation operations and load the linked program
directly into the main memory.
II. Linkage editor: this linker produces a linked version of
the program called as a load module or an executable
image.
III. Dynamic linker: this. Scheme postpone the linking
function until execution time. Any subroutine is loaded
and linked to the rest of program when it is first called.

What is software?
Computer Instructions or data, anything that can
be stored electronically is Software.
Types of Software
System Software
Application Software
Utility Software

SOFTWARE
APPLICATION
SOFTWARE
SYSTEM
SOFTWARE
UTILITY
SOFTWARE

System Software includes the Operating System and all the
utilities that enable the computer to function.
System software is a term referring to any computer software
which manages and controls the hardware so that application
software can perform a task.
Example:
Operating Systems, Compiler, Loader, Linker, Interpreter.

This is a general purpose program or acollection of
program written by the user to solve a particular
problem.
Application Software includes programs that do real work
for user.
Example:
Payroll systems, Inventory Control, Manage student
database, Word Processor, Spreadsheet and Database
Management System etc.,

these are readymade routines that are incorporated
into the computer utility software are generally
called as application oriented readymade system
programs
Example:
Soundblaster , sidekick etc.

Linker and Loader Explained

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