Programs and Programming Languages
Computers are known to provide capability to make rapid calculations, compare and make decisions, and send messages through communication links to geographically scattered places, etc.
The organization of these capabilities into a system which is capable of solving problems and realizing aims depends on computer programs. The process of telling a computer what to do and how to do is called programming. The set of instructions is known as the program.
Programs are considered to be an integral part of computer systems: they have been given the name “software” to indicate that they are distinct from but parallel to the “hardware”.
More exactly, software includes not only the computer programs but also their documentation and the training required for people to use total system and operate and maintain the programs.
Computers can deal with different kinds of problems if they are given the right instructions for what to do. Instructions are first written in one of the high-level language, e.g. FORTRAN, COBOL, ALGOL, PL/I, PASKAL, or C, depending on the type of program, and it cannot be processed by the computer until it has been compiled, which means interpreted into machine code .Usually a single instruction writtenin a high-level language, when transformed into a machine code, results in several instructions. Here is a brief description of some of the many high–level languages:
FORTRAN -acronym for FORmula TRANslation. This language is used for solving scientific and mathematical problems. It consists of algebraic formulae and English phrases. It was introduced in the United States in 1954.
COBOL -acronym for Common Business-Oriented Language. This language is used for commercial purposes. COBOL, which is written using English statements, deals with problems that do not involve a lot of mathematical calculations. It was first introduced in 1959.
ALGOL -acronym for ALGOrithmic Language .Originally called IAL, which means International Algebraic Language. It is used for mathematical and scientific purposes. ALGOL was first introduced in Europe in 1960.
PL/I - Programming Language I. It was developed in 1964 to combine features of COBOL and ALGOL. Consequently, it is used for data processing as well as scientific applications.
BASIC - acronym for Beginner’s All–purpose Symbolic Instruction Code. It was developed in 1965 at Dartmouth College in the United States for use by students who require a simple language to begin programming.
C - developed in the 1970s to support the UNIX operating system. C is a highly portable general–purpose language.
Other such languages are APL (developedin 1962), PASCA L (named after Blaise Pascal and developed in 1971), LISP and PROLOG, both of which are used for work in artificial intelligence. LOGO is a development of LISP which has been used to develop computer–based training (CBT) packages.
When a program written in one of these high–level languages is designed to do a specific type of work such as to calculate a company’s payroll or calculate the stress factor on a roof, it is called an applications program. Institutions either purchase these programs as packages or commission their own programmers to write them to meet the specifications of the users.
The program produced after the source program has been converted into machine code is referred to as an object program or object module. This is done by a computer program calledthe compiler, which is unique for each computer.
The compiler is a systems program which may be written in any language, but the computer’s operating system is a true systems program which controls the central processing unit (C P U), the input, the output, and the secondary memory devices. Another systems program is the linkage editor, which fetches required systems routines and links them to the object module (the source program in machine code). The resulting program is then called the load module, which is the program directly executable by the computer. Although systems programs are part of the software, they are usually provided by the manufacturer of the machine.
Unlike systems programs, software packages are sold by various vendors and not necessarily by the computer manufacturer. They are a set of programs designedto perform certain applications which conform to the particular specifications of the user.