What is an Assembler? [Definition, Working, & Types]

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What is an Assembler? [Definition, Working, & Types]

Sameeksha Medewar
Last updated on July 20, 2024

    Like a compiler and interpreter, an assembler is a language processor that accepts the assembly language code and produces the equivalent machine code.

    Before you embark on your journey to learn programming , it is essential to understand the types of language processors available. This blog post explains everything about an assembler.

    An assembly language is a low-level programming language used to interact with a computer’s hardware directly. Unlike a machine language that uses only binary numbers (0s and 1s), the assembly language consists of binary and hexadecimal characters. It is a bit easier to understand than the machine language.

    However, computers and other devices do not understand instructions written in programming languages other than machine language. So, when you write a program in the assembly language, you need to use an assembler to convert it into machine code.

    What is an Assembler?

    An assembler is a software program that converts the assembly language code into machine code (a pattern of 0s and 1s), making it easy for computers to interpret and process.

    Simply put, it is a piece of software that translates instructions written in the assembly language into binary code that is easily understood and processed by a computer’s CPU .

    An assembler is also referred to as a compiler of the assembly language . This is because a compiler converts high-level language into machine code. An assembler also performs the same task of generating the machine code but for the assembly language.

    How Does an Assembler Work?

    An assembler takes the assembly language code, assembles it, and converts it into the object code. An object code is a sequence of bits (0s and 1s) that a computer’s processor can execute directly and generate output.

    Let us understand in detail how an assembler works.

    • The assembler accepts the assembly language source code from a programmer.
    • It parses each line of the source code and identifies the symbolic names associated with instructions and data.
    • Further, it allocates memory to each instruction and data (value) in the source code.
    • Meanwhile, the assembler uses a program counter (PC) or location counter (LC), which maintains the memory address of the next instruction in the process.
    • It maintains a symbol table and mnemonic table. The mnemonic table helps the assembler determine which mnemonic operation code corresponds to instruction or data in the source code. Similarly, the symbol table determines the corresponding symbolic name of each instruction or data.
    • The assembler then converts the symbolic operation code into its numeric bit configuration called machine code.
    • The machine code consists of machine code instructions, data values, and memory addresses. It is saved in a separate file, which is loaded into a computer’s main memory for execution.

    While performing the above process, the assembler also keeps track of syntax and logical errors, unresolved symbols, and other issues in the source code.

    Types of Assemblers

    The two basic types of assemblers are one-pass and multi-pass assemblers. They are categorized based on the number of times the assembler parses the source code to translate it into machine code.

    1. One-Pass Assemblers

    One-pass or single-pass assemblers scan the entire assembly language code in one go and translate it into machine language code. They complete the above process of assembling the source code in a single scan.

    2. Multi-Pass Assemblers

    In multi-pass assemblers, or more specifically, two-pass assemblers, the assembly language source code is converted into equivalent machine code in two scans. First, the assembler creates a symbol table to record and process all symbolic instructions. In the second pass, it produces the machine code.


    This was all about an assembler. An assembler is a language processor that translates the assembly language program into its equivalent machine code. It is available in two types – one-pass and multiple-pass – based on the number of times it scans the source code.

    We hope this article was good enough to help you get a better understanding of an assembler.

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