DOS filename extensions — executable identification: Which filename extension is used by DOS to identify executable program files?

Introduction / Context:
DOS recognizes programs by their filename extensions. Knowing which extensions are executable helps when launching software, diagnosing path issues, and writing batch files.

Given Data / Assumptions:

• DOS executes files whose extensions are in the PATHEXT-like behavior for the era: COM, EXE, and BAT.
• Question asks for the extension that identifies an executable program.
• We assume default DOS behavior without shell replacements.

Concept / Approach:

In DOS, commands can be internal (within COMMAND.COM) or external (COM, EXE, BAT). Among the listed extensions, EXE is the standard portable executable format for DOS programs, alongside COM (simpler binary) and BAT (batch scripts). SYS files are typically drivers or configuration components, not directly executed via the shell like standard applications.

Step-by-Step Solution:

Verification / Alternative check:

DOS manuals note search order when you enter a command name: internal commands first, then look for .COM, .EXE, and .BAT files in that order on the current directory and PATH.

Why Other Options Are Wrong:

• INF: informational files; not executable.
• PRO: not a standard DOS executable extension.
• SYS: device drivers or system settings; typically loaded by CONFIG.SYS.
• None of the above: incorrect because EXE is correct.

Common Pitfalls:

Forgetting that .COM is also executable; however, since it is not listed, EXE is the best answer given. Confusing .SYS driver loading with normal program execution.

Final Answer:

EXE