The output of /proc/ioports provides a list of currently registered port regions used for input or output communication with a device. This file can be quite long. The following is a partial listing:

0000-001f : dma1 
0020-003f : pic1 
0040-005f : timer 
0060-006f : keyboard 
0070-007f : rtc 
0080-008f : dma page reg 
00a0-00bf : pic2 
00c0-00df : dma2 
00f0-00ff : fpu 
0170-0177 : ide1 
01f0-01f7 : ide0 
02f8-02ff : serial(auto) 
0376-0376 : ide1 
03c0-03df : vga+ 
03f6-03f6 : ide0 
03f8-03ff : serial(auto) 
0cf8-0cff : PCI conf1 
d000-dfff : PCI Bus #01 
e000-e00f : VIA Technologies, Inc. Bus Master IDE   
e000-e007 : ide0   
e008-e00f : ide1 
e800-e87f : Digital Equipment Corporation DECchip 21140 [FasterNet]   
e800-e87f : tulip

The first column gives the I/O port address range reserved for the device listed in the second column.