NUL, AUX, CON, COM1-4, LPT1-3, and PRN

CLOCK$ - System clock
CON - Console; combination of keyboard and screen to handle input and output
AUX or COM1 - First serial communicationport
COMn - Second, Third, ... communicationport
LPT1 or PRN - First parallel port
NUL - Dummy port, or the "null device" which we all know under Linux as /dev/null.
CONFIG$ - Unknown