High-level & Low- Level programming language

High-level programming language

From Wikipedia, the free encyclopedia

Jump to: navigation, search

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 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 designed for computers was Plankalkül, created by Konrad Zuse.^[2] However, it was not implemented in his time, and his original contributions were largely isolated from other developments (it influenced Heinz Rutishauser's language "Superplan").
Assembly language was very confusing so higher level language was introduced:This language is the closest to the english language

Contents 1 Abstraction penalty 2 Relative meaning 3 Execution models 4 See also 5 References 6 External links

Abstraction penalty

While high-level languages are intended to make complex programming simpler, low-level languages often 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.^[3][4][5] 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. In many cases, critical portions of a program mostly in a high-level language can be hand-coded in assembly language, leading to a much faster or more efficient optimised program.
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.^[6] High Level Languages are designed independent of structure of a specific computer.This facilitates executing a program written in such a language on different computers.

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.
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.

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 each program line following the program flow, converts it to machine code, and executes it; the machine code is then discarded, to be interpreted anew if the line is executed again.

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 lower-level programming language for which native code compilers are already widely available. The C programming language and Python are a common target for such translators.

 

 

 

Low-level programming language

From Wikipedia, the free encyclopedia

Jump to: navigation, search

This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (December 2009)

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 program written in a low-level language can be made to run very quickly, and with a very small memory footprint; an equivalent program 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. By comparison, a high-level programming language isolates the execution semantics of a computer architecture from the specification of the program, which simplifies development. Low-level programming languages are sometimes divided into two categories: first generation, and second generation.

Contents 1 Machine code 2 Assembly 3 Low-level programming in high-level languages 4 Relative meaning 5 See also

Machine code

Machine code is the only language a microprocessor can process directly without a previous transformation. Currently, programmers almost never write programs directly in machine code, because it requires attention to numerous details which a high-level language would handle automatically, and also requires memorizing or looking up numerical codes for every instruction that is used. For this reason, second generation programming languages provide one abstraction level on top of the machine code. Example: A function in 32-bit x86 machine code to calculate the nth Fibonacci number:

8B542408 83FA0077 06B80000 0000C383
FA027706 B8010000 00C353BB 01000000
B9010000 008D0419 83FA0376 078BD98B
C84AEBF1 5BC3

Assembly

Assembly language is considered a low-level language because while it is not a microprocessor's native language, an assembly language programmer must still understand the microprocessor's unique architecture (such as its registers and instructions). These simple instructions are then assembled directly into machine code. The assembly code can also be abstracted to another layer in a similar manner as machine code is abstracted into assembly code. Example: The same Fibonacci number calculator as above, but in x86 assembly language using MASM syntax:

fib:
    mov edx, [esp+8]
    cmp edx, 0
    ja @f
    mov eax, 0
    ret
    
    @@:
    cmp edx, 2
    ja @f
    mov eax, 1
    ret
    
    @@:
    push ebx
    mov ebx, 1
    mov ecx, 1
    
    @@:
        lea eax, [ebx+ecx]
        cmp edx, 3
        jbe @f
        mov ebx, ecx
        mov ecx, eax
        dec edx
    jmp @b
    
    @@:
    pop ebx
    ret

Low-level programming in high-level languages

Experiments with hardware support in high-level languages in the late 1960s led to such languages as PL/S, BLISS, BCPL, and extended ALGOL for Burroughs large systems being used for low-level programming. Forth also has applications as a systems language. However, the language that became pre-eminent in systems programming was C. C is considered a third generation programming language, since it is structured and abstracts from machine code (historically, no second generation programming language emerged that was particularly suitable for low-level programming). However, 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. C's ability to abstract from the machine level means that the same code can be compiled for different hardware platforms; however, fine-grained control at the systems level is still possible providing that the target platform has certain broadly-defined features in place, such as a flat memory model, and memory that is divided into bytes. C programmes may require a certain amount of 'tweaking', often implemented by conditional compilation, for different target platforms. The process of adapting a systems programme for a different platform is known as porting. Example - a function that calculates the nth Fibonacci number in C

unsigned int fib(unsigned int n)
{
    if (n <= 0)
        return 0;
    else if (n <= 2)
        return 1;
    else {
        int a,b,c;
        a = 1;
        b = 1;
        while (1) {
            c = a + b;
            if (n <= 3) return c;
            a = b;
            b = c;
            n--;
        }
    }
}

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". Many programmers today might refer to C as low-level. 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.