An executable file in Windows is a file that has a .exe file extension and contains instructions that are executed by the operating system. It can be used to execute a program or perform an action on a computer. An executable file contains machine code, as well as other data such as resource forks and other meta-data that the operating system needs to execute the program correctly. Executable files for Windows are typically stored in the Program Files directory on the C: drive.
Executable files have a specific format in Windows. The first 64 bytes of an executable file is known as the “DOS header”. This section contains information specific to the operating system, such as the number of bytes in the file, the operating system version and type, the date and time the file was created, and other related information. Following the DOS header is the actual code and data of the executable. This code and data consists of various bytes that must follow a certain structure and order in order to be readable and understood by the operating system.
The code of the executable file is usually divided into sections. The most common sections are the code section, the data section, and the resource section. The code section contains the actual instructions for the computer to execute; these instructions are written in assembly language. The data section contains variables and constants that the program needs to access. The resource section contains graphical elements such as dialog boxes, icons, and images that the program needs in order to function properly.
These sections are further divided into blocks of data called segments. A segment will generally contain several hundred or thousand bytes of data, depending on the program. Each segment is given a unique name, and this segment name is what the operating system uses to identify the segment. As each segment is read, the operating system will check the segment names and ensure that they are correct before loading and executing the program.
An executable file also contains other information besides the code and data, such as debug information and the addresses of global variables. Debug information makes it easier for developers to debug their programs, while the addresses of global variables provide the program with an indirect way of accessing data that is stored outside of the program’s main code block.
Finally, the executable file also contains a group of bytes known as the relocation table. This table contains information that allows the operating system to relocate parts of a program if the address space it was linked to becomes unavailable. This relocation information is used to prevent a program from crashing when the operating system needs to move it to another address space.
In summary, the format of an executable file in Windows is comprised of a DOS header, code and data sections, segment names, global variables, and a relocation table. These respective components make it possible for the operating system to read and execute the instructions of the program, as well as providing a means of debugging and relocating the program if necessary.