A character device is any device that processes data one byte (one character) at a time. The computer's keyboard, screen, real-time clock, and serial and parallel ports are character devices.
Each character device has a name. MS-DOS uses the following names:
| Name | Description |
| AUX | Auxiliary device, usually a serial communications port. |
| CLOCK$ | Real-time clock. |
| COM1 | First serial communications port. AUX is usually an alias for COM1. |
| COM2 | Second serial communications port. |
| CON | Keyboard and screen. |
| LPT1 | First parallel printer port. PRN is usually an alias for LPT1. |
| LPT2 | Second parallel printer port. |
| LPT3 | Third parallel printer port. |
| NUL | “Bit bucket” device that discards all output and provides no input. |
| PRN | Printer device (also called a list device), usually a parallel communications port. |
Programs open character devices by supplying the device names to Open File with Handle (Interrupt 21h Function 3Dh). The functions use the device names much as they use filenames, opening the device and returning a file handle. Once a program has a handle, it can read from, write to, and close the device by using such file-handle functions as Read File or Device (Interrupt 21h Function 3Fh), Write File or Device (Interrupt 21h Function 40h), and Close File with Handle (Interrupt 21h Function 3Eh).
Note:
A program cannot create a file with the same filename as a device (such as CON.TXT), regardless of the extension. Attempting to open or create a file with the same name as a device opens the device instead.