title: I/O-mapped I/O - are port addresses a part of the RAM
body: <p>In I/O-mapped I/O (as opposed to memory-mapped I/O), a certain set of addresses are fixed for I/O devices. Are these addresses a part of the RAM, and thus that much physical address space is unusable ? Does it correspond to the 'Hardware Reserved' memory in the attached picture ?</p>
  
  <p>If yes, how is it decided which bits of an address are to be used for addressing I/O devices (because the I/O address space would be much smaller than the actual memory. I have read this helps to reduce the number of pins/bits used by the decoding circuit) ?</p>
  
  <p>What would happen if one tries to access, in assembly, any address that belongs to this address space ?</p>
  
  <p><img src="https://i.stack.imgur.com/wJdLG.png" alt="&#39;Hardware Reserved&#39; memory"></p>