What is assembly language (ASM)?

Assembly language acts as a intermediary between machine code and high-level languages, offering more direct communication with the hardware. Each processor family has its own assembly language, closely linked to its specific architecture.

A assembly program converts assembly language instructions into machine code, facilitated by tools known as assemblers. This translation work is necessary in order for essential components of a device to run, such as the operating systems and the device drivers.

Although assembly language has a steep learning curve, provides an in-depth understanding of hardware-level operations. In the following sections, we will explore its operation, differences with high-level languages and practical examples to illustrate its application in programming.

How does an assembly language work?

Assembly language is a language of low-level programming, and is translated into machine code by an assembly program. Each assembly instruction corresponds to a specific operation in the processor, representing in symbolic form the binary instructions of the machine code.

The assembler manages the organisation of memory and references to memory and generates an object file with the equivalent machine code after processing the source code.

Despite their efficiency, the assembly language programs require a detailed understanding of the processor architecture, so they have a steep learning curve compared to high-level languages. However, it offers unparalleled control over the system. Therefore, assembly language is a highly valued technical skill in programming jobs that involve interacting with hardware.

Uses of assembly language

Assembly language is still used today, although its use is less frequent than in the past due to the advancement and increasing versatility of high-level languages, which are easier to read and use. However, assembly remains relevant in certain specific areas of programming.

Although there are alternatives such as high-level languages and advanced compilation techniques, assembler is still irreplaceable in situations where absolute control over the hardware is needed or where CPU cycles have to be modified. Its use, although more specialised, has not disappeared.

Assembly language is typically used in the following cases:

• Direct hardware manipulation: It is used to interact precisely with the physical components of the computer. For example, it allows direct control of input and output ports, handling system interrupts or accessing specific memory addresses. 
• Access to processor instructions: Provides direct access to the processor's entire instruction set, including those not available in high-level languages. This allows you to take advantage of processor-specific features, such as SIMD (Single Instruction, Multiple Data) instructions for parallel processing, or specialised instructions for cryptography. 
• Resolution of critical performance situations: It is used to optimise sections of code that are bottlenecks in terms of performance. For example, in real-time signal processing applications, high-end video games, or 3D rendering software.

Assembly language vs. high-level language

The programming languages are classified into high-level and low-level languages. While high-level languages such as Python o Java are designed to be understandable and to abstract most of the details of the hardware, assembly language is a low-level language which provides detailed control over the hardware. 

Assembly language programming is more complex and requires a deeper understanding of how computer hardware works, but offers faster and more efficient execution.

Difference between assembly language and machine code

The machine code is the most basic form of language that a computer can understand and execute, consisting of zeros and ones. Assembly language, on the other hand, uses mnemonics and symbols to represent operations and data, making it more human-readable. 

For example, an addition operation could be translated in machine code as 1010, while in assembly language it could be ADD. 

In addition, while all devices can read machine code regardless of platform, the assembly language programs are inextricably linked to the specific architecture of the processor for which they are designed.

How is assembly language translated into machine code?

The translation from assembly language to machine code is a straightforward process that is carried out by a program called assembler. This process is much simpler than high-level language compilation, since there is an almost one-to-one correspondence between assembly instructions and machine code instructions.

The assembler reads the source code written in assembly language. It then translates each mnemonic instruction into its machine code equivalent using a processor-specific mapping table. During this process, it converts labels and symbols to concrete memory addresses, and calculates absolute addresses for relative references. Finally, it generates an output file with the resulting machine code, which consists of a series of binary instructions that the processor can execute directly.

Is assembly language intermediate code?

Assembly language and the intermediate code are two distinct concepts in the field of software programming and compilation, each with its own purpose and characteristics. 

The main difference lies in its purpose and level of abstraction. While assembly language is a programming language in itself, used to write low-level programs, intermediate code is a temporary representation within the compilation process.

Unlike assembly language, intermediate code is independent of processor architecture and is generated during the compilation process. Its main function is to facilitate code optimisation and improve cross-platform portability.

Most widely used assembly languages

There are several assembly languages, each designed for a specific processor architecture. The most widely used include NASM (Netwide Assembler), MASM (Microsoft Macro Assembler) and GAS (GNU Assembler), each targeting specific processor architectures. 

They have been instrumental in operating systems development y device drivers. The choice between these languages will depend on the processor architecture and project requirements. 

Its mastery enables deep understanding and meticulous control over hardware, facilitating performance optimisation in critical software.

Example of assembly language

To illustrate what an assembly language program looks and works like, let's explore a basic example that adds two numbers together. The exact syntax may vary between different assembly languages, but here is an example in NASM assembly language:

In this code:

1. We define a data section (section .data) where the variables num1 and num2 are stored with values 5 and 3 respectively.

2. Then, in the text section (.text section), we define the entry point of the programme (_start).

3. Within _start, we use the mov instruction to load the value of num1 into the AL register.

4. Next, we use the add instruction to add the value of num2 to the AL register, leaving the result of the addition (8) in AL.

This example highlights the low-level nature of assembly language programming, in which registers and memory are directly manipulated. 

Furthermore, it shows how basic arithmetic operations require multiple steps compared to high-level languages, where this operation could be performed with a simple expression result = num1 + num2.

Conclusions

Assembly language offers unprecedented control over the computer hardware, allowing you to develop highly efficient programmes. However, its inherent complexity and the need for a detailed understanding of the hardware make it challenging to learn and implement. 

Despite this, learning assembly language gives us an insight into how a computer really works at the most basic level, and can be of great value for certain areas of programming.

Things to remember

• Assembly language is a low-level programming language.
• An assembly program translates assembly language source code into machine code.
• Assembly languages are specific to the processor architecture.
• Compared to high-level languages, assembly language provides more direct and detailed control over the hardware.
• Programming in assembly language requires a thorough understanding of computer hardware and architecture.
• Examples of popular assembly languages include NASM, MASM and GAS.
• The key difference between assembly language and machine code lies in readability and processor architecture specificity.