Programming a Digital Computer

Programming involves the preparation and writing of detailed inst­ructions for a computer. These instructions tell a computer exactly what data to use and what sequence of operations to perform with the data. Without such programs, a computer could not solve problems or deliver any other desired result.
In most cases, computer scientists and other computer specialists called programmers write the instructions. They refer to programs as software because the instructions have no physical parts. The term hardware is applied to the computer itself, including its electronic circuits and peripheral equipment.
A programmer writes the instructions for a computer in a programming language. Such a language consists of letters, words, and symbols as well as rules for combining those elements. Some programming languages closely resemble the language of mathematics. Others enable programmers to write instructions in simple, everyday expressions, such as "READ", "ADD", and "STOP". Programming languages of this kind are called high-level languages.
The language that a programmer uses depends largely on the job to be done. If a task involves processing business data, the programmer would most likely use COBOL (COmmon Business Oriented Language). However, preparing a computer to solve complicated scientific problems might require the use of ALGOL (ALGOrirhmic Language), which is a mathematically oriented programming language.
Some high-level languages can be used for business, technical, or scientific programming. Such languages include FORTRAN (FORmula TRANslation); APL (A Programming Language); and PL/I (Programming ''.Language One).
Another commonly used programming language is BASIC (Beginner's All-purpose Symbolic Instruction Code). BASIC is well suited for writing relatively simple programs for minicomputers and microcom­puters.
Some computer programs may be written in an assembly language. This kind of language is harder to use than a high-level language because it involves symbols as well as words. For example, an assembly language might use the symbols AD for add and S for subtract.
A computer cannot work directly with a program written in a high-level or assembly language. The instructions have to be translated into a machine language composed of binary digits that represent operation codes, memory addresses, and various symbols, such as plus and minus signs. Machine language is also known as low-level language. Special programs called compilers and assemblers translate high-level and assemb­ly languages into machine language.