They also may not be supported in Windows file dialog boxes. The extended character set includes the line, greek, foreign language and miscellaneous other symbols. To type these characters, hold down ALT and enter the three digit numeric value of the character on the numeric keypad . Extensions are 0 to 3 characters long. They are separated from the filename by a period.
Extensions have the same character restrictions as filenames.
Executable text files have a .BAT extension. See the sections on batch files for more detail. This list is just the tip of the iceberg. Every disk in DOS has the concept of a current directory, a directory where a file will be read or written if no other directory is specified. You do not have just one current directory.