FREE ESSAY ON PROGRAMMING

PROGRAMMING

PROGRAMMING 
A program is a sequence of instructions that tells the hardware of a computer what
operations to perform on data. Programs can be built into the hardware itself, or they
may exist independently in a form known as software. In some specialized, or dedicated,
computers the operating instructions are embedded in their circuitry; common examples are
the microcomputers found in calculators, wristwatches, automobile engines, and microwave
ovens. A general-pur pose computer, on the other hand, contains some built-in programs
(in ROM) or instructions (in the processor chip), but it depends on external programs to
perform useful tasks. Once a computer has been programmed, it can do only as much or as
little as the software controlling it at any given moment enables it to do. Software in
widespread use includes a wide range of applications programs-instructions to the
computer on how to perform various tasks. 
Languages. 
A computer must be given instructions in a language that it understands-that is, a
particular pattern of binary digital information. On the earliest computers, programming
was a difficult, laborious task, because vacuum-tube ON-OFF switches had to be set by
hand. Teams of programmers often took days to program simple tasks such as sorting a list
of names. Since that time a number of computer languages have been devised, some with
particular kinds of functioning in mind and others aimed more at ease of use-the
user-friendly approach. 
Machine Language. 
Unfortunately, the computer's own binary-based language, or machine language, is
difficult for humans to use. The programmer must input every command and all data in
binary form, and a basic operation such as comparing the contents of a register to the
data in a memory-chip location might look like this: 11001010 00010111 11110101 00101011.
Machine-language programming is such a tedious, time consuming, task that the time saved
in running the program rarely justifies the days or weeks needed to write the program. 
Assembly Language. 
One method programmers devised to shorten and simplify the process is called
assembly-language programming. By assigning a short (usually three-letter) mnemonic code
to each machine-language command, assembly-language programs could be written and
debugged-cleaned of logic and data errors-in a fraction of the time needed by
machine-language programmers. In assembly language, each mnemonic command and its
symbolic operands equals one machine instruction. An assembler program translates the
mnemonic opcodes (operation codes) and symbolic operands into binary language and
executes the program. 
Assembly language, however, can be used only with one type of CPU chip or microprocessor.
Programmers who expended much time and effort to learn how to program one computer had to
learn a new programming style each time they worked on another machine. What was needed
was a shorthand method by which one symbolic statement could represent a sequence of many
machine-language instructions, and a way that would allow the same program to run on
several types of machines. These needs led to the development of so-called high-level
languages. 
High-Level Languages. 
High-level languages often use English-like words-for example, LIST, PRINT, OPEN, and so
on-as commands that might stand for a sequence of tens or hundreds of machine-language
instructions. The commands are entered from the keyboard or from a program in memory or
in a storage device, and they are intercepted by a program that translates them into
machine-language instructions. 
Translator programs are of two kinds: interpreters and compilers. With an interpreter,
programs that loop back to re-execute part of their instructions reinterpret the same
instruction each time it appears, so interpreted programs run much more slowly than
machine-language programs. Compilers, by contrast, translate an entire program into
machine language prior to execution, so such programs run as rapidly as though they were
written directly in machine language. 
The first commercial programmer was probably Grace Hopper (1906-92), an American. After
programming an experimental computer at Harvard University, she worked on the UNIVAC I
and II computers and developed a commercially usable high-level programming language
called FLOWMATIC. To facilitate computer use in scientific applications, IBM then
developed a language that would simplify work involving complicated mathematical
formulas. Begun in 1954 and completed in 1957, FORTRAN (FORmula TRANslator) was the first
comprehensive high-level programming language that was widely used. 
In 1957, the Association for Computing Machinery set out to develop a universal language
that would correct some of FORTRAN's perceived faults. A year later they released ALGOL
(ALGOrithmic Language), another scientifically oriented language; widely used in Europe
in the 1960s and 1970s, it has since been superseded by newer languages, while FORTRAN
continues to be used because of the huge investment in existing programs. COBOL (COmmon
Business Oriented Language), a commercial and business programming language, concentrated
on data organization and file handling and is widely used today in business. 
BASIC (Beginner's All-purpose Symbolic Instruction Code) was developed at Dartmouth
College in the early 1960s for use by nonprofessional computer users. The language came
into almost universal use with the microcomputer explosion of the 1970s and 1980s.
Condemned as slow, inefficient, and inelegant by its detractors, BASIC is nevertheless
simple to learn and easy to use. Because many early microcomputers were sold with BASIC
built into the hardware (in ROM memory) the language rapidly came into widespread use. As
a very simple example of a BASIC program, consider the addition of the numbers 1 and 2,
and the display of the result. This is written as follows (the numerals 10-40 are line
numbers): 
10 A=1
20 B=2
30 C=A+B
40 Print C
Although hundreds of different computer languages and variants exist, several others
deserve mention. PASCAL, originally designed as a teaching tool, is now one of the most
popular microcomputer languages. LOGO was developed to introduce children to computers.
C, a language Bell Laboratories designed in the 1970s, is widely used in developing
systems programs, such as language translators. LISP and PROLOG are widely used in
artifical intelligence (q.v.) . 
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