CMD File

What are CMD files and how to open them

Are you having problems opening a CMD file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your CMD files.

What is a CMD file?

CMD files have multiple uses, and 1dir+ Additionals Commands Definition is one of them. Read more about the other uses further down the page.

1dir+ Additionals Commands Definition

1dir+ Additionals Commands Definition files hold custom command definitions used by the MS-DOS file manager called 1Dir+ (also written as Idir+). These definitions let the file manager include extra actions beyond the built-in ones, such as creating new directories, running external programs, or specifying commands to execute automatically, to tailor the file management workflow.

These files are produced and read by 1Dir+ itself. When 1Dir+ is configured or customized, it writes or loads these Additional Commands Definition files so the user can extend the menu of commands available in the shell-like interface of 1Dir+. The manager uses the definitions in these files to show options like AUTO, NEWDIR, RUNS, and ENDDEF in its command menus.

Internally, the file begins with the ASCII signature COMMAND followed by a space (bytes 43-4F-4D-4D-41-4E-44 20) at the start. It also contains lines or fields labelled ENDDEF, NEWDIR, AUTO, RUNS among other keywords, which identify the boundaries and types of custom commands defined within.

How to open CMD files

Important: Different programs may use files with the CMD file extension for different purposes, so unless you are sure which format your CMD file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested five different CMD openers which you will find listed below.

Last updated: August 31, 2026

All known file formats using extension .CMD

While 1dir+ Additionals Commands Definition is a popular type of CMD-file, we know of 2 different uses of the .CMD file extension. Different software may use files with the same extension for different types of data.

PCOS Executable

PCOS Executable files hold machine-code programs for the Olivetti M20's PCOS (Professional Computer Operating System). They are generated by assembling and linking source code (from Assembly language, or optionally from the Pascal or C compiler) to produce a binary that PCOS can load and run. They serve as utility programs, resident or non-resident commands, device drivers, and other executable routines for the system. The PCOS COMMAND LINE INTERPRETER treats executables just like utility commands built into the OS.

Executable files are produced by the PCOS Linker (or "ldpcos" in later toolchains). The linker takes object files generated by the Assembler or Pascal (or C with appropriate tools), combines them into one binary, writes headers for load format, sets an entry point, and marks whether the executable is "transient" (loaded, run, and then unloaded) or "resident" (loaded and stays in RAM). Files ending in CMD are transient; files with extension SAV are resident. Resident executables are usually used for system services or commands that should remain in memory indefinitely.

As technical identifiers, PCOS Executable files typically begin at offset 0 with two bytes whose value is 0x0200. Additionally, at offset 3 there is the ASCII string "TLOC" (hex 54 4C 4F 43).

Various apps that use files with this extension

These apps are known to open certain types of CMD files. Remember, different programs may use CMD files for different purposes, so you may need to try out a few of them to be able to open your specific file.

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