Article by Ayman Alheraki on January 11 2026 10:35 AM
In the world of programming and operating systems, the executable header is a crucial component that helps the system load and interpret the binary structure of a program, guiding it on how to execute the file correctly. Each operating system uses its own executable header format, which serves as a blueprint to inform the system on how to interact with and execute the binary. In this article, we’ll dive into the various executable header types across different operating systems in a detailed and insightful way.
The executable header is a data structure located at the beginning of an executable file. It contains essential information that helps the operating system prepare and run the program. This information often includes the target processor type, entry points, and different tables with crucial data such as sections, linking symbols, and sometimes dynamic linking libraries.
Windows uses the Portable Executable (PE) format, which is based on the Common Object File Format (COFF). This format is commonly used for executable files (.exe) and dynamic link libraries (.dll) in Windows. The PE/COFF header has several important fields that define the structure of the file.
DOS Header: Every PE file begins with a DOS header that displays the message “This program cannot be run in DOS mode” if the file is run on an incompatible system.
PE Signature: Marks the beginning of the PE header with the signature “PE\0\0” in binary encoding.
File Header: Contains information about the target device and file properties, such as the number of sections.
Optional Header: Includes vital details like the Entry Point, file start address, and code size.
Section Table: Lists sections in the file where data and executable instructions are stored, such as the Text, Data, and Resource sections.
Linux uses the ELF (Executable and Linkable Format), a flexible format that supports multiple architectures. ELF files are used to execute programs and shared libraries on Linux.
ELF Header: Contains information like the file type (executable or library), target architecture (x86, x64, ARM, etc.), and entry points.
Program Header Table: Contains sections used by the operating system to load the executable file into memory.
Section Header Table: Specifies locations of different sections within the file, such as the text section, data section, and dynamic linking section.
String Table and Symbol Table: Hold symbol names and memory locations used in the program.
macOS uses the Mach-O (Mach Object) format, which is specifically designed for executable files and dynamic libraries in macOS and iOS. Mach-O is known for its high flexibility and ability to support both dynamic and static libraries.
Mach Header: Contains the target processor type, number of load commands, and file type (executable, dynamic library, etc.).
Load Commands: A set of commands that contain information about how the file should be loaded into memory, including section addresses and entry points.
Segment and Section Tables: Define the different sections such as text and data sections.
Symbol Table: Used to identify function and variable symbols within the executable file and link them to memory locations.
Android relies on the ELF format for compiled code but also uses the DEX (Dalvik Executable) format for files that are run in the Dalvik virtual machine or Android Runtime (ART).
Similar to the ELF used in Linux, with some modifications to suit the Android environment.
Contains the ELF Header, Program Header Table, and Section Header Table, just like ELF files on Linux.
DEX Header: Contains the file signature, file size, and necessary information for parsing the file.
String IDs and Type IDs: Define data types, class names, and methods.
Class Definitions: Specify the classes, their methods, and fields in the program.
iOS also uses the Mach-O format, like macOS, but depends on LLVM Intermediate Representation (IR) during development for greater compatibility across Apple’s processors.
The same as those in macOS, containing the Mach Header, Load Commands, and Segment and Section Tables.
LLVM IR: Used in the compilation process to ensure compatibility across various iOS devices, which may contain different processors.
| Operating System | Header Type | Key Features |
|---|---|---|
| Windows | PE/COFF | Suitable for x86 and x64 architectures; contains DOS Header, PE Signature, and Optional Header. |
| Linux | ELF | Multi-architecture support; highly flexible with Program Header and Section Header. |
| macOS | Mach-O | Advanced structure with Load Commands to simplify dynamic loading. |
| Android | ELF/DEX | Uses ELF for compiled code and DEX for Dalvik/ART-based programs, providing compatibility with the Java environment. |
| iOS | Mach-O | Supported by LLVM IR for better device compatibility, uses Mach-O for rapid performance. |
The executable header is a fundamental part of every binary file, guiding the operating system on how to load and execute the program correctly. Each OS has a unique header structure designed to optimize program performance and system compatibility. Understanding these headers can help developers handle binary files more effectively, improving application performance and avoiding compatibility issues across platforms.