HIGH LEVEL LANGUAGE

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 more portable across platforms. Such languages hide the details of CPU operations such as memory access models and management of scope.
This greater abstraction and hiding of details is generally intended to make the language user-friendly, as it includes concepts from the problem domain instead of those of the machine used. A high-level language isolates the execution semantics of a computer architecture from the specification of the program, making the process of developing a program simpler and more understandable with respect to a low-level language. The amount of abstraction provided defines how "high-level" a programming language is.^[1]
The first high-level programming language to be designed for a computer was Plankalkül, created by Konrad Zuse. However, it was not implemented in his time and his original contributions were isolated from other developments.

[edit] Features

The term "high level language" does not imply that the language is superior to low-level programming languages—in fact, in terms of the depth of knowledge of how computers work required to productively program in a given language, the inverse may be true. Rather, "high-level language" refers to the higher level of abstraction from machine language. Rather than dealing with registers, memory addresses and call stacks, high-level languages deal with variables, arrays, objects, complex arithmetic or boolean expressions, subroutines and functions, loops, threads, locks, and other abstract computer science concepts, with a focus on usability over optimal program efficiency. Unlike low-level assembly languages, high-level languages have few, if any, language elements that translate directly into a machine's native opcodes. Other features such as string handling routines, object-oriented language features and file input/output may also be present.

[edit] Abstraction penalty

Stereotypically, high-level languages make complex programming simpler, while low-level languages tend to produce more efficient code. Abstraction penalty is the barrier that prevents high-level programming techniques from being applied in situations where computational resources are limited. High-level programming features like more generic data structures, run-time interpretation and intermediate code files often result in slower execution speed, higher memory consumption and larger binary program size ^[2][3][4]. For this reason, code which needs to run particularly quickly and efficiently may require the use of a lower-level language, even if a higher-level language would make the coding easier.

However, with the growing complexity of modern microprocessor architectures, well-designed compilers for high-level languages frequently produce code comparable in efficiency to what most low-level programmers can produce by hand^{[citation needed]}, and the higher abstraction may allow for more powerful techniques providing better overall results than their low-level counterparts in particular settings.^[5]

[edit] Relative meaning

The terms high-level and low-level are inherently relative. Some decades ago, the C language, and similar languages, were most often considered "high-level", as it supported concepts such as expression evaluation, parameterised recursive functions, and data types and structures, while assembly language was considered "low-level". Many programmers today might refer to C as low-level, as it lacks a large runtime-system (no garbage collection etc.), basically supports only scalar operations, and provides direct memory addressing. It therefore readily blends with assembly language and the machine level of CPUs and microcontrollers.

Also note that assembly language may itself be regarded as a higher level (but often still one-to-one if used without macros) representation of machine code, as it supports concepts such as constants and (limited) expressions, sometimes even variables, procedures, and data structures. Machine code, in its turn, is inherently at a slightly higher level than the microcode or micro-operations used internally in many processors. See C2's page about high-level languages.

[edit] Execution models

There are three models of execution for modern high-level languages:

Interpreted 

Interpreted languages are read and then executed directly, with no compilation stage. A program called an interpreter reads the program line by line and executes the lines as they are read.

Compiled 

Compiled languages are transformed into an executable form before running. There are two types of compilation:

Machine code generation 

Some compilers compile source code directly into machine code. This is the original mode of compilation, and languages that are directly and completely transformed to machine-native code in this way may be called "truly compiled" languages.

Intermediate representations 

When a language is compiled to an intermediate representation, that representation can be optimized or saved for later execution without the need to re-read the source file. When the intermediate representation is saved it is often represented as byte code. The intermediate representation must then be interpreted or further compiled to execute it. Virtual machines that execute byte code directly or transform it further into machine code have blurred the once clear distinction between intermediate representations and truly compiled languages.

Translated 

A language may be translated into a low-level programming language for which native code compilers are already widely available. The C programming language is a common target for such translators.