EVOLUTION OF SYSTEM EVOLUTION OF SYSTEM

PROGRAMMINGPROGRAMMING

BASICS

What is system programming…???

System programming is the activity of programming system software.

systems programming aims to produce software which provides services to the computer hardware . It requires a greater degree of hardware awareness.

Reasons for the evolution of system programs-

1)To make computer better adapted to the need of users.

2)People wanted more assistance in the mechanics of preparing their program.

We will discuss about the evolution of following components of system programming-

ASSEMBLERSLOADERSLINKERS MACROSCOMPILERS

ASSEMBLER

Initially the users were compelled to write their program in machine code (a series of 0 and 1).

But the programmer found it difficult to write or read programs in machine code.

Now the users began to use some mnemonic (symbol) for each machine instruction, which they subsequently translate into machine language.

Such a mnemonic machine language is called assembly language.

Programs known as assembler were written to automate the translation of assembly language to machine code.

The input to the assembler is called the source program and the output is a machine language translation(object program).

LOADERS

A loader is a system program that places programs into memory and prepares them for execution.

Once the assembler produces an object program, that program must be placed into memory and executed.

It is the purpose of loader to assure that object programs are placed in memory in an executable form.

MACROS

First you should know what is subroutine..?

A subroutine is a body of computer instruction designed to be used by other routines to accomplish a task.

There are two types of subroutine-

Open subroutine Close subroutine

Open subroutine or Macroswhose code is inserted in the main

program(flow continues).Thus if the same open subroutine is called

four times, it would appear in four different places in the calling program.

Closed subroutineIt can be stored outside the main routine,

and control transfers to the subroutine.

NEED OF MACROS-

To relieve programmers of the need to repeat identical parts of their program operating system provide a macro processing facility, which permits the programmer to define an abbreviation for a part of his program and to use this abbreviation in his program. The macro processor treats the identical parts of the program defined by the abbreviation as a macro definition and saves the definition.

COMPILERS

As the user’s problems became more categorized into areas such as

scientificBusiness Statistical problems

Some high level languages were developed that allowed the user to express certain problems concisely and eaisly.

Ex-FORTRAN,COBOL,ALGOL…..

A compiler is a system program that accepts program written in HIGH level language and produces an object program.

Modern compilers must be able to provide the complex facilities that programmers are now demanding.