I think David Chalmers defines (hard) consciousness fairly effectively. It is the sensations, such as colors, smells, and sounds that we experience when we are awake. There are many open questions as far as how to explain, detect, quantify, and localize it, but Chalmers has managed to at least partition it off from other peripheral concepts.
Ted Talk
Intelligence, on the other hand, is a very nebulous term that can mean very different things to different people.
We can program computers to perform tasks such as mathematical calculations or playing chess that most would consider human intellectual capabilities, although I seriously doubt that a mechanical adding machine or a chess program experiences consciousness. In fact, you could create a game-playing program that is purely lookup-based (whenever you see this board position, make that move) that I am fairly certain would not experience consciousness, but that might appear to behave intelligently.
Anyone who has watched the occasional motions of a sleeping dog or cat would be inclined to believe that they are dreaming, and that, consequently, they probably also experience consciousness, even though they probably would not qualify for MENSA.
Despite significant continuing progress, we are still very far away from a fairly comprehensive understanding of how the human brain functions, and even further away from how those signal processing functions give rise to consciousness and thought. And due to the nested manner that the brain has evolved, I suspect that the physical reality of human consciousness is probably quite complex.
My best guess is that there could be a certain inherent level of consciousness in any system, animal or machine, IF it constructs an internal representation of itself and itâs surrounding environment, provided that it can remember selected parts of that model (attention) for future recall and analysis. Other parts of the world model that may be immediately acted upon, but are not remembered, might be analogous to what we call the subconscious.
One compelling reason why I believe that machines could be conscious is the hypothetical Gedankenexperiment mentioned by Murry Shanahan where your entire brain is very carefully removed, sliced up, and scanned so that an accurate and comprehensive model of all your neurons can be constructed and simulated on a computer. If you carefully interface this software process to cameras and microphones and ask it if it is conscious, it would insist that it is. It would be able to recall vividly your past experiences. If you showed it a red apple, and asked it what color it was experiencing, it would say that it is the exact same red that it experienced in the past. To it, conscious experience halted when your brain was removed, and resumed when the simulation process began running.