Features of Amiga Executable Files
Amiga executable files can be launched either from the graphical shell of the Amiga, the Workbench, from the Amiga's command line interpreter (called CLI, later AmigaShell), or even from a file manager tool.
No particular filename extension is required for Amiga executable files. For example, the calculator applet "Calculator" can be renamed to "Calculator.com", "Calculator.exe", "Calculator.bin", or even "Calculator.jpeg". These are all valid names for programs or tools, because AmigaOS does not differentiate between file extensions.
Some operating systems, such as MS-DOS or Windows, need filename extensions to recognize that a file is an executable. Usually, this extension is a three-character acronym separated from the real filename by a period ".".
AmigaOS adopted another method to recognize it is dealing with a valid executable. There is a particular sequence of bytes in the file header, yielding the hexadecimal value $000003f3. This sequence, which signifies an executable file and lets it be self-running, is called a magic cookie (from the magic cookies in Alice's Adventures in Wonderland by Lewis Carroll).
This kind of solution to identify executables on the Amiga was taken from similar solutions which were adopted by UNIX/Unix-like operating systems, where magic cookies are called magic numbers.
In Unix, a file attribute bit "x" (for eXecutable) must also be set, only in this case the operating system will check the magic number. If there is a correct magic number in the beginning of the file it is considered a binary executable. If a file starts with characters "#!" then it is considered to be a script instead.
Read more about this topic: Amiga Hunk
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