Microsoft MS-DOS reserves certain names for system device drivers. If you try to name a file using one of these names, you will receive the following error message: The solution is to change the file name.

Below is a list of default device driver names.

   Name    Function
   ----    --------
   CON     Keyboard and display
   PRN     System list device, usually a parallel port
   AUX     Auxiliary device, usually a serial port
   CLOCK$  System real-time clock
   NUL     Bit-bucket device
   A:-Z:   Drive letters
   COM1    First serial communications port
   LPT1    First parallel printer port
   LPT2    Second parallel printer port
   LPT3    Third parallel printer port
   COM2    Second serial communications port
   COM3    Third serial communications port
   COM4    Fourth serial communications port
				

To identify system device driver names, use one of the following two commands:

•	mem /d | more
•	debug d 0070:0000