COMMAND.COM
COMMAND.COM is a command-line interpreter for DOS, Windows 9x, and OS/2 operating systems. It serves as the primary user interface for executing system commands, batch files, and internal commands in these environments.
History and Development
- Early Versions: The origins of COMMAND.COM trace back to the 86-DOS, which was later renamed to PC-DOS when acquired by IBM for its IBM PC. This command interpreter was developed by Microsoft under the name MS-DOS.
- Evolution: With each new version of DOS, COMMAND.COM was updated to include new commands, improved functionality, and better support for hardware.
- Windows 9x: In Windows 95, 98, and ME, COMMAND.COM was retained for compatibility with older applications and batch files, even though the Windows Command Prompt (cmd.exe) was introduced.
Functionality
- Internal Commands: These are built into COMMAND.COM, like
DIR, COPY, and DEL. They do not require external files to execute.
- External Commands: These are separate executable files located in the system's PATH, such as
FORMAT.COM or EDIT.COM.
- Batch File Execution: COMMAND.COM processes batch files, which are text files containing a series of commands to be executed in sequence.
- Environment Variables: It manages environment variables, allowing users to set, modify, or query variables like
PATH, PROMPT, and COMSPEC.
Limitations and Criticism
- Memory Constraints: Due to the limitations of the DOS memory model, COMMAND.COM had to fit within the memory restrictions of the time, leading to limitations in its capabilities.
- Functionality: It lacked many features of modern shells like command history, tab completion, and advanced scripting capabilities.
- Security: COMMAND.COM did not have robust security features, which could lead to issues like command injection vulnerabilities in batch files.
Replacements and Legacy
- cmd.exe: With Windows NT, Microsoft introduced cmd.exe as a more powerful command-line interpreter, retaining COMMAND.COM for backwards compatibility.
- POSIX: Efforts like Windows Subsystem for Linux (WSL) provide a more Unix-like command line environment, diminishing the role of COMMAND.COM.
External Links