What Is Assembly Language? Working, Features, and Advantages

• Assembly language is defined as a type of programming language designed to be used by developers to write programs that can run directly on a computer’s central processing unit (CPU).
• It is a low-level language, which means it is closer to the machine code the CPU can execute, making it more powerful than other higher-level languages such as C++, Java, or Python.
• This article explains assembly language, its working, features, and key advantages.

What Is Assembly Language?

Assembly language is a type of programming language that is designed to be used by developers to write programs that can run directly on a computer’s central processing unit (CPU). It is a low-level language, which means it is closer to the machine code the CPU can execute, making it more powerful than other higher-level languages such as C++, Java, or Python.

In an assembly language program, each instruction represents a single operation that the computer’s CPU can perform. These can include simple arithmetic and logical operations, such as adding and subtracting values, as well as more complex operations that involve manipulating data stored in the computer’s memory. Assembly language programs are typically written in a text editor and then assembled using a specialized software tool called an assembler.

One key benefit of using assembly language is that it allows programmers to write highly optimized code for the specific hardware a program will run on. This is because assembly language instructions map directly to the machine language instructions that the CPU can execute. By writing code optimized for the hardware, programmers can create programs that run faster and more efficiently than those written in higher-level languages.

Another benefit of assembly language is that it allows programmers to directly access the computer’s hardware resources, such as its memory and input/output ports. This makes it an ideal language for systems programming, which involves writing code that interacts with the operating system and the computer’s hardware devices. For example, a device driver, software that allows an operating system to communicate with a particular hardware device, can be written in assembly language to ensure that it is optimized for the device’s specific hardware.

Programming in assembly language can be challenging, though, particularly for programmers who are used to working with higher-level languages. Since assembly language is low-level, it requires a greater understanding of computer hardware and how the CPU executes instructions. Additionally, assembly language programs tend to be more verbose than equivalent programs written in higher-level languages, making them harder to read and maintain.

To help make assembly language programming more manageable, assemblers typically include several features designed to simplify the process. One of these features is the use of symbolic names to represent memory addresses and other constants used in the program. For example, a programmer might use a symbolic name to represent that address rather than directly using a numeric memory address in an instruction. This makes the program easier to read and understand and also makes it easier to modify in the future.

Assemblers may also include support for macros, which are small code snippets that can be used to define reusable pieces of code. Macros allow programmers to avoid repeating the same code multiple times, saving time and reducing the likelihood of introducing errors in the code.

Despite its challenges, assembly language remains important for systems programming and low-level software development. Since it provides direct access to hardware resources and allows for highly optimized code, it is often used in applications such as embedded systems or device drivers. It is also used in reverse engineering, where programmers analyze existing software to understand how it works or modify it to perform different functions.

Evolution of assembly language

Assembly language has been used since the earliest days of computer programming, evolving along with the hardware architecture of computers. Here’s a brief overview of the evolution of the language.

• First generation (1940s to 1950s): The first generation of computers, mostly vacuum tube-based, were programmed using machine language, a set of instructions represented as binary numbers. Assembly language emerged as an abstraction of machine language, using mnemonics to represent binary instructions in a more human-readable format.
• Second generation (1950s to 1960s): This generation of computers used transistor-based technology and had more sophisticated instruction sets, which allowed for the development of more complex assembly languages. The first high-level programming languages, such as FORTRAN and COBOL, were also developed during this time.
• Third generation (1960s to 1970s): The third generation of computers saw the widespread adoption of integrated circuits, which allowed for more powerful and compact machines. Assembly languages continued to evolve during this time, with new features such as macros and symbolic labels being added to assemblers to make programming easier.
• Fourth generation (1970s to 1980s): This generation of computers saw the emergence of microprocessors, which led to the development of microcomputer systems such as the Apple II and the IBM PC. Assembly languages for these systems were designed to be more user-friendly, with features such as syntax highlighting and automatic indentation.
• Fifth generation (1980s to present): This generation of computers saw the emergence of massively parallel processing systems and the development of more complex software systems. Assembly language continued to evolve, with new features such as advanced debugging and optimization tools being developed to help programmers write more efficient code.

Today, assembly language is still used for systems programming, device driver development, and other low-level programming tasks. However, it is no longer as widely used as it once was since higher-level programming languages have become more powerful and easier to use. According to a recent research study by 6sense, PHP, Python, C#, and C++ are amongst the most popular programming languages used globally in 2023, with a market share of 34.97%, 0.95%, 0.35%, and 0.10%, respectively.

However, despite the widespread adoption of such high-level languages, assembly language remains an important tool for certain programming tasks. It also continues to be taught in computer science programs worldwide.

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How Does Assembly Language Work?

The syntax of assembly language varies depending on the specific machine architecture it is being used with. However, most assembly languages share a few basic features. Assembly language programs are typically made up of a series of instructions written using a combination of mnemonic codes and operands, representing the data being manipulated by the instruction.

Let’s understand how assembly language works in detail.

How Assembly Language Works

Step 1: Writing the code

The first step is to write the code in assembly language. Assembly language code consists of mnemonic instructions that correspond directly to the machine language instructions executed by the CPU. 

For example, here is a code in x86 assembly language that adds two numbers: 

mov abx, 5 ; move the value 5 into the abx register

mov cdx, 7 ; move the value 7 into the cdx register

add abx, cdx ; add the values in abx and cdx and store the result in abx 

In this code, the first two lines set the values of the abx and cdx registers. The third line adds the values in the abx and cdx registers and stores the result in the abx register.

Step 2: Assembling the code

The next step is to assemble the code using an assembler. An assembler is a program that converts the assembly language code into machine language the computer can execute. The assembler reads the assembly code and translates it into binary machine code, a series of 0s and 1s representing the instructions and data in the program.

When the assembler converts the assembly code into machine code, it generates a file with an .obj extension containing the machine code and other information that the linker uses to create the final executable file.

Step 3: Linking the code

The next step is to link the code. Linking is the process of combining the object file generated by the assembler with any necessary system libraries to create an executable program. During the linking process, the linker resolves any external references to functions or variables and combines all the object files into a single executable file.

Step 4: Load into the memory

Once the code has been linked, it needs to be loaded into memory. The operating system accomplishes this. The executable file is loaded into a specific location in memory, and the operating system sets up the program’s environment, including its stack, heap, and global variables.

Step 5: Executing the program

The final step is to execute the program. When the CPU reads the instructions, it will execute them one by one. The machine code instructions generated by the assembler correspond directly to the assembly language instructions in the original code.

In the example above, the first two lines move the values 5 and 7 into the abx and cdx registers, respectively. The third line adds the values in the abx and cdx registers and stores the result (12) in the abx register.

This is a simple example; however, assembly language can be used to write complex programs that can control hardware directly. Assembly language is still used in certain areas, such as embedded systems, real-time systems, and operating system development, where control over the hardware is necessary.

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Key Features of Assembly Language

Assembly language has several key features that make it an inevitable part of the software development process.

Assembly Language Key Features

1. Mnemonic instructions

Assembly language uses mnemonic instructions to represent machine code instructions. These are short, easy-to-remember words representing specific instructions that the computer’s processor can understand. For example, the mnemonic ‘MOV’ stands for ‘move’ and is used to move data from one location to another.

2. Direct access to hardware

Assembly language provides direct access to hardware resources such as the CPU, memory, and I/O ports. This allows programmers to write code that can control these resources directly. For instance, assembly language can be used to write a code (i.e., a device driver) that interacts directly with a piece of hardware such as a printer or network card.

3. Low-level abstraction

Assembly language provides a close-to-hardware abstraction of the underlying computer system. This allows programmers to write specific code that takes advantage of a particular hardware feature of a given computer system. For example, assembly language can be used to write algorithms for tasks such as sorting and searching.

4. Efficient use of resources

Assembly language programs are built for the hardware on which they run. This allows them to use system resources such as memory and processing power efficiently. For instance, assembly language can be used to write code that uses memory more efficiently than any other higher-level languages such as C#, JavaScript, or PHP.

5. Full control over program flow

With assembly language, programmers can gain complete control over the flow of their programs. This allows for more fine-grained control over program execution through constructs such as loops and conditionals. For example, assembly language can be used to write code implementing complex logic that cannot be easily expressed using higher-level languages such as Swift or Ruby.

6. Direct access to memory

Assembly language programs have direct access to a computer system’s memory. This allows programmers to write code that can directly manipulate the data stored in memory. For instance, assembly language can be used to write code that implements complex data structures such as linked lists and binary trees.

7. Better control over CPU

Assembly language provides better control over the CPU, allowing programmers to write code that can perform operations such as setting flags and manipulating registers directly. This level of control can be important for tasks such as systems programming, where it is necessary to interact directly with the operating system and the CPU.

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Advantages of Assembly Language

Assembly language can facilitate fast and efficient code writing. Although coding in assembly language is quite complex, the language is much more flexible than other high-level languages.

Here are some of the key benefits of assembly language.

1. Display flexibility

Assembly language provides a high degree of flexibility in displaying data on the screen, thanks to its data-stream commands, wide screens, and cursor-dependent functions.

Data-stream commands are used to write data to the screen in real-time. This allows assembly language programs to display information as it is generated without the need to store it in memory first. For example, a program might use data-stream commands to display the output of a sensor reading or the results of a calculation.

Wide screens refer to displays with a large number of pixels or columns. Assembly language provides the ability to control each pixel or column on the screen, allowing programmers to create custom graphics and user interfaces. Wide screens are particularly useful in applications such as video games or multimedia presentations.

Cursor-dependent functions are used to control the position of the cursor on the screen. This allows assembly language programs to create user interfaces with menus, buttons, and other interactive elements. For example, a programmer can use cursor-dependent functions to create a menu allowing users to select different options.

2. Specific data handling

Assembly language provides powerful tools to handle special data scenarios, such as managing reentrancy into global data structures or complex functions at operator logoff.

Reentrant code can be safely called by multiple threads or processes simultaneously without interfering with each other. In the context of assembly language, this means that multiple programs or processes can execute the same code simultaneously without causing conflicts. This is particularly useful for updating global data structures shared across multiple programs or processes. Assembly language provides powerful synchronization primitives such as semaphores and locks that can be used to ensure that multiple programs or processes can access global data structures safely and without conflicts.

Complex functions at operator logoff or abend-reinstatement refer to situations where a program must execute complex code when the user logs off or an error occurs. In these situations, assembly language provides a way to save the program’s state and resume execution later. This is accomplished using interrupts and signal handlers, which allow the program to handle unexpected events and take appropriate action. For example, the program will save its state when the user logs off and resume execution when the user logs back in.

3. Access to privileged functions

Privileged functions are supported by assembly language, such as access to macros, by providing instructions that can only be executed in privileged mode. Macros are pre-defined sets of instructions that a program can call. They are often used to simplify programming tasks and increase code reusability.

Assembly language provides access to system macros only available in privileged mode, allowing programmers to perform tasks such as system calls, memory allocation, and process management. By providing access to these macros, assembly language enables programmers to develop low-level software with direct access to system resources and can perform privileged operations.

4. Interaction with other commands

Assembly language supports interaction with other commands, such as examining the status of or waiting on asynchronous or timed events, by providing instructions that allow the programmer to control the flow of the program based on specific conditions. For example, this language provides instructions that can check the status of input/output (I/O) operations and wait for those operations to be completed before proceeding with the program.

The language also provides instructions that allow the programmer to delay the execution of the program for a specified period, which is useful for handling timed events. This is often done using interrupts, which are signals the system uses to communicate with devices and other programs.

Assembly language provides instructions that allow a programmer to enable or disable interrupts and handle interrupt requests when they occur. This allows the program to interact flexibly and responsively with other commands, such as I/O operations or timed events, making it well-suited for developing low-level software that requires direct access to hardware and system resources.

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Takeaway

The future of assembly language will likely be more specialized and focused on specific use cases such as low-level software development, performance optimization, and hardware control. As high-level programming languages become more advanced, the need for assembly language in general software development may decline. However, it will likely remain relevant in areas such as embedded systems, operating systems, and vulnerability research, where low-level access to hardware and system resources is necessary.

With the growing use of specialized hardware for AI and ML, such as GPUs or FPGAs, assembly language may become more important for optimizing the performance of these systems.

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