machinecodes

Machine code, or machine language, is the lowest-level programming language that a computer's central processing unit (CPU) can execute directly. It consists of a sequence of binary instructions, where each instruction encodes an operation and its operands in a form specific to a processor's instruction set architecture (ISA). The term "machine code" is often used interchangeably with machine language. Machine code is architecture-specific: the same binary pattern does not produce the same operation on different CPUs.

Machine code is typically generated from higher-level languages by compilers, or from assembly language by an assembler. Assembly provides mnemonic representations of opcodes and operands, making it easier to read and write, but ultimately the assembler translates it into machine code. Some systems also use just-in-time compilation or ahead-of-time compilation to produce executable machine code.

An instruction in machine code has a defined format, including an opcode that specifies the operation and one or more operand fields that indicate data or memory addresses. Common concepts include addressing modes, immediate values, registers, and memory operands. Instruction lengths vary: some architectures use fixed-length instructions (RISC), others permit variable-length instructions (CISC).

During execution, the CPU fetches an instruction from memory, decodes it to determine the operation, and executes it, often as part of a pipeline. The performance of code depends on the efficiency of the ISA, instruction lengths, and features such as pipelining, out-of-order execution, and caching. Endianness determines how multi-byte values are stored in memory.

Examples of instruction set architectures include x86-64, ARM, MIPS, and RISC-V. Each provides its own set of machine codes and encoding rules. Understanding machine code is essential for low-level systems work, debugging, reverse engineering, and performance tuning, though most software developers work at higher levels and rely on compilers to emit suitable machine code.