External commands and Internal commands
Dos commands can be divided into external commands and internal commands, and internal commands are contained in a file named Command.com, which resides in memory when the system starts. External commands are files that are saved in C:\Windows\System32 that can be directly valid files, including. exe files,. com files,. bat files.
The role of path in system variables is to boot the system from the root directory set in path, find the matching path, and make a new path to execute the file. If the path variable is improperly set, the system will not be able to find the relevant file and thus make an error. System default system variable the value of path is C:\Windows\System32. This means that after the user enters the file name at the command prompt, the system will automatically go to the C:\Windows\System32 directory to find the file, regardless of which command prompt the user enters. If the value of path does not contain C:\Windows\System32, the user can only enter ping after the command prompt is C:\Windows\System32 to execute the ping file. And you enter ping at any command prompt, such as on my computer, after c:\Documents and SETTINGS\LSR, which is what the system would think of the ping file in the c:\Documents and SETTINGS\LSR directory. But the ping file is actually located in the C:\Windows\System32 directory, this time there is no file found error.
Workaround:
Right-click My brain-Properties, advanced-environment variables--in the system variable, select name path or path-> edit, add a c:\windows\system32 to the variable value
"Ping" is not an internal or external command, or a program or batch file that can be run, when you use the ping command in
cmd or other telnet or nestat