.COM File Extension
DOS Command File
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What is a COM file?
A COM file is an executable program capable of being run by MS-DOS and Windows. It is saved in a binary format and is similar to an .EXE file, but differs in that it has a maximum size of roughly 64KB and it has no header or metadata. COM files are commonly used for executing a set of instructions whereas EXE files are used for fully developed programs.
Most Windows users will not encounter COM executable files since the files are primarily used in MS-DOS. However, you may acquire an old COM file that stores a program or commands and need to run it in Windows.
You can run a COM file in the 32-bit version of Windows but you will be prompted to install the NT Virtual DOS Machine (NTVDM) component when you launch the file for the first time. You can also run a COM file in the 64-bit version of Windows with a virtual machine that supports the MS-DOS environment.
NOTE: If a folder includes both EXE and COM files with the same filename (e.g., run.exe and run.com), the DOS or Windows command prompt will run the COM file if you type the filename without the extension.
Common COM Filenames
COMMAND.COM - The Windows shell program used by DOS and Windows 95, 98, and Me. It was replaced by cmd.exe in later versions of Windows.
EICAR.COM - A file developed by the European Institute for Computer Antivirus Research (EICAR). It is used to test antivirus programs.
While COM files typically store legitimate MS-DOS or Windows programs, they may also be used for distributing and executing malware attacks on victims' computers. To protect against malicious Windows executable attacks, do not double-click a COM file you have downloaded, received, or found on your computer unless you trust the source of the file.