Computer Programming Languages

                      Computer programming language, any of various languages for expressing a set of detailed instructions for a digital computer. Such instructions can be executed directly when they are in the computer manufacturer-specific numerical form known as machine language, after a simple substitution process when expressed in a corresponding assembly language, or after translation from some “higher-level” language. Although there are over 2,000 computer languages, relatively few are widely used.

- Machine language

                          Machine code or machine language is a system of impartible instructions executed directly by a computer's central processing unit. Each instruction performs a very specific task, typically either an operation on a unit of data (in a register or in memory, e.g. add or move), or a jump operation (deciding which instruction executes next, often conditional on the results of a previous instruction). Every executable program is made up of a series of these atomic instructions. Machine code may be regarded as a primitive (and cumbersome) programming language or as the lowest-level representation of a compiled and/or assembled computer programme. While it is possible to write programs in machine code, because of the tedious difficulty in managing CPU resources, it is rarely done any more, except for situations that require the most extreme optimization. This language is used in the first generation computers and when we writing programmes in machine language we have to use binary digits (0, 1). 

                         Almost all executable programmes are written in higher level languages, and translated to executable machine code by a compiler and linker. Machine code is sometimes called native code when referring to platform-dependent parts of language features or libraries.

                          Programmes in interpreted languages are not represented by machine code, however, their interpreter (which may be seen as a processor executing the higher level programme) often is. Machine code should not be confused with so called "bytecode", which is executed by an interpreter.

- High level languages

                          A high-level programming language is a programming language with strong abstraction from the details of the computer. In comparison to low-level programming languages, it may use natural language elements, be easier to use, or be from the specification of the programme, making the process of developing a programme simpler and more understandable with respect to a low-level language. The amount of abstraction provided defines how "high-level" a programming language is. Also this is a  programming language such as C, Ada, Algol, BASIC, COBOL, C, C++, FORTRAN, LISP, Pascal, Prolog, or FORTRAN that enables a programmer to write programmes that are more or less independent of a particular type of computer. Such languages are considered high-level because they are closer to human languages and further from machine languages. In contrast, assembly languages are considered low-level because they are very close to machine languages.  

                         The first high-level programming language to be designed for a computer was Plankalkul, created by Konrad Zuse. However, it was not implemented in his time and his original contributions were isolated from other developments.

- Low level languages

                          In computer science, a low-level programming language is a programming language that provides little or no abstraction from a computer's instruction set architecture. Generally this refers to either machine code or assembly language. The word "low" refers to the small or nonexistent amount of abstraction between the language and machine language; because of this, low-level languages are sometimes described as being "close to the hardware."

                                Low-level languages can be converted to machine code without using a compiler or interpreter, and the resulting code runs directly on the processor. A programme written in a low-level language can be made to run very fast, and with a very small memory footprint; an equivalent programme in a high-level language will be more heavyweight. Low-level languages are simple, but are considered difficult to use, due to the numerous technical details which must be remembered.

- Language translators

                           A computer can only understand programmes defined using machine code. Consequently a programme written for example in a high level language such as Java cannot be run directly. To execute a computer programme written in high or low level language, it must be first being translated.

                             There are 3 types of system software used for translating the code that a Programmer writes into a form that the computer can execute (i.e. machine code). These are:

                    1.  Assemblers

                    2.  Compilers

                    3.  Interpreters

Source Code is the code that is input to a translator.

Executable code is the code that is output from the translator.

Assembler

                                  Assembler is a computer programme to translate between lower-level representations of computer programmes. An assembler converts basic computer instructions into a pattern of bits which can be easily understood by the computer and the processor can use it to perform its basic operation. An Assembler converts an assembly program into machine code.

Compiler

                                A compiler is a computer programme (or set of programs) that transforms source code written in a programming language(the source language) into another computer language (the target language, often having a binary form known as object code). The most common reason for wanting to transform source code is to create an executable programme. Compiler converts source code to executable code line by line. 

                                 The name "compiler" is primarily used for programmes that translate source code from a language to a lower level language (e.g., assembly language or machine code). If the compiled programme can run on a computer whose CPU or operating system is different from the one on which the compiler runs, the compiler is known as a cross-compiler. A programme that translates from a low level language to a higher level one is a decompiler. A programme that translates between high-level languages is usually called a language translator, source to source translator, or language converter. A language rewriter is usually a programme that translates the form of expressions without a change of language.

Interpreter

                            Interpreter is a program that executes instructions written in a high-level language. There are two ways to run programmes written in a high-level language. The most common is to compile the programme; the other method is to pass the programme through an interpreter.

                           When we converting a computer programme to machine language by using interpreter it converts the programme to machine language line by line.