/dev/port vs /dev/mem

I need some clarification. I can directly write to /dev/port to get direct access to a parallel port and it works fine (I can turn on LEDs plugged into the port connector). However, I thought I could do the same with /dev/mem? (http://tldp.org/LDP/khg/HyperNews/get/devices/fake.html). When I try to read and write to /dev/mem I get no errors, but the writes never seem to be reflected on the external connector. I ask just because this isn't what I expected based on what I've read about writing to /dev/mem.

Can you not access ioports via /dev/mem?

Throwing in a handful of suggestions (untested). It could be that...

• Writing to memory position 0x378 directly requires being in real mode to have the desired effect (since it may be remapped in Protected Mode).
• The use of /dev/mem requires that the hardware has been MMIO-mapped, and you also need to know the MMIO address (which usually is not 0x378).