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Assembly Language

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Assembly language is a method of abstracting machine code instructions for a computer into commands recognizable by a human. Instead of dealing directly with bit sequences, programmers write programs in assembly by generating blocks of code using a small set of keywords (which are mapped to machine instructions by an assembler).

Assemblers not only relieve the programmer of remembering instruction codes, but allow symbolic reference to memory locations, further improving redability.

An example Hello World program written in pseudo-assembly for a MS-DOS-based system is listed below. Original source: Assembly Language for the IBM-PC.


 .data
   hello_message db 'Hello, World!',0dh,0ah,'$'
 
 .code
 main proc
   mov ax,@data
   mov ds,ax
 
   mov ah,9
   mov dx,offset hello_message
   int 21h
 
   mov ax,4C00h
   int 21h
 main endp
 end main

Assembly programs are much easier to understand than their corresponding machine code instruction streams, which are just numbers, but they are much more difficult to comprehend than most general-purpose higher-level programming languages, such as the C programming language or Java. There are, however, higher-level programming languages such as APL that are unreadable by other than a specialist.