Machine Language vs. Assembly Language: Key Differences

1. Origin

However, the credit for “inventing” machine language cannot be given to a single person. Instead, it evolved as early computer systems were developed and engineers sought more efficient ways to program them.

The first computer systems to be programmed using machine language existed in the mid-20th century. Before that, early computers like the UNIVAC and ENIAC would be programmed using plugs and switches, which were time-consuming and difficult to operate.

In fact, these challenges were the reason for the development of machine language. The ability to write code using binary numbers made it considerably simpler for programmers to perform more complex operations.

It was late 1948 when the Electronic Delay Storage Automatic Calculator (EDSAC) had an assembler integrated into its bootstrap program. It leveraged one-letter mnemonics developed by David Wheeler, credited as the creator of the first “assembler.”

A few years later, in 1955, an assembly language known as the Symbolic Optimal Assembly Program (SOAP) was written by Stan Poley for the IBM 650 computer.

Assembly languages went one step ahead of machine language. They eliminated much of the tedious, time-consuming, and error-prone operations seen in the first-generation programming of the earliest computers. They freed programmers from tasks such as calculating addresses and remembering numeric codes, thereby becoming the standard for many types of programming.

Several programs were written using only assembly language. It was only in 1961 that the Burroughs MCP was introduced — this was the first computer whose operating system was not developed using only assembly language. Instead, its OS was written in Executive Systems Problem Oriented Language (ESPOL).

Assembly language had (and, to a certain extent, still has) commercial applications. For instance, a considerable portion of the IBM mainframe software by corporations was written using assembly language.

In commercial applications, the biggest advantages of assembly language included minimal bloat and overhead, as well as greater reliability and speed.

However, assembly language was not only used commercially. As computers became more commonplace, assembly language also entered people’s homes.

2. Development

However, machine language and assembly language did not always coexist. The latter was only introduced in the 1950s, giving users access to mnemonics or symbolic representations of machine language instructions.

This made it simpler for programmers to understand and write code. However, assembly language still required a detailed understanding of the underlying machine language.

With the advent of higher-level programming languages like COBOL, BASIC, and FORTRAN, English-like commands became commonplace and non-technical people could learn how to program more easily. Even then, however, machine language remained popular for developing low-level software such as operating systems.

In the decades before the turn of the millennium, more advanced programming languages like C and C++ were introduced, making it possible for programmers to write code that could be ported between different computer systems. Even then, machine language remained a mainstay in developing low-level software like firmware and device drivers.

And while machine language may seem obsolete today, it still sees usage in developing low-level software. However, it is being replaced by modern programming languages like Java and Python. This is because modern hardware and software technologies support code written at a higher abstraction level, thus simplifying software development and maintenance.

While machine language may seem the same as assembly language, that is not the case. Unlike assembly language, machine language is not a “traditional” programming language in that it is no longer intended for human use. Instead, it is the lowest-level representation of a computer program. A machine language consists of binary code executed directly using computer hardware.

One reason for this was the interpreted BASIC dialects on these systems leading to insufficient execution speed and unsatisfactory facilities for taking complete advantage of available system hardware.

Popular examples of assembly language programs included the Turbo Pascal compiler, the IBM PC DOS operating systems, and even early programs such as the spreadsheet processor Lotus 1-2-3 and the 1993 arcade game NBA Jam. Interestingly, assembly language was chosen to enhance the performance of the Sega Saturn, a gaming console well-known for its development challenges.

The use of hand-coded assembly language was even seen in early microcomputers, including in operating systems and large applications. Assembly language allowed developers to address system challenges such as severe resource constraints, imposed idiosyncratic display and memory architectures, limited and buggy services, and the lack of first-class high-level language compilers for microcomputers.

FORTRAN, COBOL, and PL/I eventually went on to displace assembly language; however, numerous large organizations still relied on assembly language application infrastructures until the turn of the millennium.

While it did not take long for the use of assembly languages to be supplanted by higher-level languages, they still see usage even today for direct hardware manipulation, addressing critical performance issues, and accessing specialized processor instructions. The typical applications of modern-day assembly languages include low-level embedded systems, real-time systems, and device drivers.

3. Applications

This strictly numerical language is the lowest-level CPU interface accessible by programmers; however, some CPUs include an even lower leveled interface known as the microcode, which implements the machine code. On regular commercial CPUs, microcode is rarely intended to be modified.

Machine language is directly mapped into a version readable by humans using assembly language, which translates machine language’s numerical opcodes and operands into readable strings.

Assembly language is also used in programs with performance-sensitive inner loops, where it provides opportunities for optimization that are otherwise difficult to achieve when using a high-level language (think linear algebra with BLAS or discrete cosine transformation).

Assembly language is useful for programs that build vectorized functions for programs in C and other higher-level languages.

It is also used in real-time programs such as flight navigation systems, medical equipment, and simulations. For instance, fly-by-wire systems require telemetry to be interpreted and executed within stringent time constraints. Thus, sources of unpredictable delays must be removed, making some interpreted languages incompatible with the application. Here, assembly language gives programmers greater transparency and management capabilities over processing details.

Similarly, assembly language can be useful for cryptographic algorithms that strictly require the same execution time every time to thwart timing attacks.

Assembly language is used in solutions that require end-to-end control over the environment. It can also be found in applications without high-level language and for new or specialized processors with no cross-compilers available.

Aside from this, it is used in instruction set simulators for tracing, debugging, and monitoring while keeping additional overhead to a minimum.

“ROM hacking” of video games can also occur by modifying program code at the assembly language level.

It can also be used for reverse-engineering and altering program files, such as existing binaries that could have been initially written in either assembly or higher-level languages.

Finally, fundamental topics like binary arithmetic, stack processing, memory allocation, character set encoding, compiler design, and interrupt processing would be difficult to study without learners first understanding how computers operate at the hardware level.

4. Use in Programming

Therefore, very few modern-day programs are written directly in machine language. This limits its applications to low-level debugging, program patching (especially in cases where the assembler source is unavailable), and cases requiring the disassembly of assembly language.

Apart from the cases mentioned above, most modern programs are written in higher-level languages or, less often, using assembly language. Utilities like assemblers, linkers, and compilers are then used to translate the source code to executable machine code. However, interpreted programs are an important exception here as they are not translated into machine language.

Interpreters can be considered executors or processors carrying out the instructions of the source code. They generally consist of directly applicable machine code generated from higher-level language source code.

It is also used in the boot code for many newer systems. Here, it serves as the low-level code that initializes and runs tests on the system hardware before the operating system is booted. It is often stored in ROM.

It is also used for low-level code like operating system kernels, which cannot depend on the availability of pre-existing system calls.

Assembly language is also used for writing code that interacts directly with hardware, such as interrupt handlers and device drivers.

Finally, this language is used for programs requiring processor-specific instructions not implemented at the compiler level. This can include, for instance, the bitwise rotation instruction that is a key part of many encryption algorithms.

5. Language Features

Microcode: Some computers implement machine language using a more fundamental layer called microcode. This underlying layer provides a common interface for machine language for various computer models with varying underlying dataflows. Using microcode facilitates the porting of machine language programs between computing models.

Bytecode: Bytecode, also called p-code, is different from machine language and is either compiled into machine language for direct execution or executed through an interpreter. However, some processors (like Java) are designed to execute specific bytecode directly as machine language.

In-memory storage: When a computer runs a program, it is stored in RAM as machine code. The CPU uses this code to perform its tasks. To improve program performance, the machine code is sometimes cached, and the CPU tracks the part of the machine code that needs to be executed by using a program counter, which is a value that guides the CPU to where in memory the next set of instructions can be found. It can be set to any memory address, but an error will be generated if the address is invalid. To help prevent this, some systems use special bits called “execute bits” to indicate if a section of memory contains code that is allowed to be executed.

Code space: When multiple programs run on the computer simultaneously, each program has its own memory section dedicated to machine language. These sections are called code spaces. In multithreading environments, different threads of a single program share the same code space, which can reduce the amount of time needed to switch between tasks. However, this can also be a security concern, as malicious actors can execute code stored in the code space.

Mnemonics: In assembly language, instructions are simple and represented by a symbolic name known as a mnemonic. The mnemonic refers to a machine language instruction, which typically consists of an operation (opcode) and one or more operands. Operands can be immediate values, registers, or data addresses stored elsewhere in memory. The assembler reflects the underlying processor architecture in how it handles the operands. Some assemblers include extended mnemonics for specialized uses and macro-instructions that generate multiple machine instructions.

Data directives: These directives allow users to define data elements to hold variables and data. They define a data type, length, alignment, and data availability for outside programs assembled separately. Data directives are classified as pseudo-ops by some assemblers.

Assembly directives: Assembly language has special commands called assembly directives or pseudo-opcodes. These directives instruct the assembler to perform operations other than assembling instructions. They can impact the object code, symbol table, and the values of internal assembler parameters. Assembly language allows programmers to associate names with memory locations and constants, making the code more self-documenting. Some assemblers also provide flexible symbol management and support for comments in the code. These comments are important as the raw assembly language can be challenging to understand without them.

Macros: These are sequences of text lines in assembly language that can include variables and constants. Macros are typically used to make assembly language programs appear shorter and to add structure to the code. Assembler macro instructions can be lengthy and include high-level language elements like variables, arithmetic operations, and string manipulation. Macros can take parameters and generate assembly language instructions based on the arguments. Despite their power, macro processing has fallen into disuse in many high-level languages but remains a staple in assembly language.