Assembler: A computer will not understand any program written in a language, other than its machine language. The programs written in other languages must be translated into the machine language. Such translation is performed with the help of software. A program which translates an assembly language program into a machine language program is called an assembler. If an assembler which runs on a computer and produces the machine codes for the same computer then it is called self assembler or resident assembler. If an assembler that runs on a computer and produces the machine codes for other computer then it is called Cross Assembler.
Assemblers are further divided into two types:
One Pass Assembler and Two Pass Assembler. One pass assembler is the assembler
which assigns the memory addresses to the variables and translates the source
code into machine code in the first pass simultaneously. A Two Pass Assembler
is the assembler which reads the source code twice. In the first pass, it reads
all the variables and assigns them memory addresses. In the second pass, it
reads the source code and translates the code into object code.
Compiler: It
is a program which translates a high level language program into a machine
language program. A compiler is more intelligent than an assembler. It checks
all kinds of limits, ranges, errors etc. But its program run time is more and
occupies a larger part of the memory. It has slow speed. Because a compiler
goes through the entire program and then translates the entire program into
machine codes. If a compiler runs on a computer and produces the machine codes
for the same computer then it is known as a self compiler or resident compiler.
On the other hand, if a compiler runs on a computer and produces the machine
codes for other computer then it is known as a cross compiler.
Interpreter: An interpreter is a program which translates statements of a
program into machine code. It translates only one statement of the program at a
time. It reads only one statement of program, translates it and executes it.
Then it reads the next statement of the program again translates it and
executes it. In this way it proceeds further till all the statements are
translated and executed. On the other hand, a compiler goes through the entire
program and then translates the entire program into machine codes. A compiler
is 5 to 25 times faster than an interpreter.
By the compiler, the machine codes are saved
permanently for future reference. On the other hand, the machine codes produced
by interpreter are not saved. An interpreter is a small program as compared to
compiler. It occupies less memory space, so it can be used in a smaller system
which has limited memory space.
Linker: In
high level languages, some built in header files or libraries are stored. These
libraries are predefined and these contain basic functions which are essential
for executing the program. These functions are linked to the libraries by a
program called Linker. If linker does not find a library of a function then it
informs to compiler and then compiler generates an error. The compiler
automatically invokes the linker as the last step in compiling a program.
Not built in libraries, it also links the user
defined functions to the user defined libraries. Usually a longer program is
divided into smaller subprograms called modules. And these modules must be
combined to execute the program. The process of combining the modules is done
by the linker.
Loader: Loader
is a program that loads machine codes of a program into the system memory. In Computing,
a loader is the part of an Operating System that is responsible for loading programs. It is one of
the essential stages in the process of starting a program. Because it places
programs into memory and prepares them for execution. Loading a program
involves reading the contents of executable
file into memory. Once loading
is complete, the operating system starts the program by passing control to the
loaded program code. All operating systems that support program loading have
loaders. In many operating systems the loader is permanently resident in
memory.
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