When the processor accesses a memory mapped register, is it actually accessing the device

Suppose a 开发者_StackOverflow中文版device has one register, and the CPU has a x86-like architecture. This register is memory mapped at physical address 0x50000.

The processor writes 0X00ABCDEF to 0x50000 (phys.). If I were able to inspect that address by "opening" a RAM bank, what should I find? 0X00ABCDEF or junk?

I assume the register of the device has 0X00ABCDEF on it already. Please, correct me if I'm wrong.

Special addresses can be mapped to "pins" of a device or other peripherals, so that RAM is not involved at all (though things are a little bit more complex nowadays, the idea is quite the same). So, accessing that address could do something according to specifications of the hardware mapped to that address, but leave no tracks in the RAM. Saying differently, that address is not a location in the RAM. It's just a way to address (to reach) the device.