Low-level programming language

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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. 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."

A low-level language does not need a compiler or interpreter to run; the processor for which the language was written is able to run the code without using either of these.

By comparison, a high-level programming 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.

Low-level programming languages are sometimes divided into two categories: first generation, and second generation.

[edit] First generation

The first-generation programming language, or 1GL, is machine code. It 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

[edit] Second generation

The second-generation programming language, or 2GL, is assembly language. It is considered a second-generation 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

[edit] See also

• High-level programming languages
• Very high-level programming languages
• Categorical list of programming languages

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