executable

An executable, in computing, is a file that contains instructions that a computer's processor can execute directly. Executables are produced from source code by compilers or assemblers, and are designed to run without requiring an interactive interpreter. They differ from scripts or source code, which require a separate program to translate or interpret them at run time.

An executable typically includes a header with metadata such as the entry point, memory layout, and format specifics, followed by sections containing machine code, data, and references to library routines. Many executables rely on libraries, either linked statically into the file or loaded dynamically at run time by the operating system.

Common executable formats reflect different operating systems. Windows uses the Portable Executable (PE) format; Unix-like systems commonly use the Executable and Linkable Format (ELF); macOS uses Mach-O. Some platforms support scripts with a shebang line that specify an interpreter, making the file directly executable by the OS but not by the CPU itself. Bytecode files, such as Java class files or .NET assemblies, are executed by virtual machine environments rather than directly by the processor.

When an executable is launched, the operating system loads it into memory, applies access permissions, and starts execution at the program's designated entry point. The loader may perform dynamic linking, resolving external references to shared libraries, and prepare the runtime environment for the process.

Executable portability is limited by architecture and operating system; recompilation or cross-compilation is typically required to run on a different platform. Security measures such as code signing, address space layout randomization (ASLR), and executable permissions help protect systems from untrusted binaries.