The written word is a serial form of communication with comprehension of each section dependent upon an understanding of the previous section. To intake the information of each page simulaneously destroys this necessary dependency. A picture, on the other hand, may be perused serially by attention wandering across the surface but possibly might be understood by taking in the total graphic relationship at once in a kind of parallel observation.

Everybody works both consciously and subconsciously all the time. If you didn't, you would't be able to do much of anything. When you read, your subconscious mind recognizes words and identifies their meanings. If you had to consciously identify each word and its meaning, you wouldn't be able to pay attention to the idea being expressed by the statements.

Reading isn't the best example. Take walking for instance. Walking requires you to use most of the muscles in your body in order to move in such a way as to maintain balance. All the muscles have to function at the same time, but you can only consciously think about one thing at a time. If you had to consciously think about each muscle in your body and which way to move it, you would never be able to walk without falling on your face. Your subconscious actually handles most of what you do in day to day life. The reason you have to practice activities to become proficient at them is because you have to train your subconscious to handle most of the job automatically.

As for parallel reading, the problem is your eyes can only focus on a few words at a time. There is no way you can focus on two pages at once, much less hundreds.

well brain works in parallel and you process block of words paralelly (if that was not known) the limitation here is not mind as per say but your sensor (eyes) how much they can grab at once. if you think you are reading, thinking about weather you agree of disagree with author and also you are feeling texture of the bookspine... so your brain is working in parallel if we can design the system that can feed two different pages one you are reading and one is fed through ears than probably you will 'feel' that you read the whole book but mind will need to be trained to get use to two feedback and making sense out of it... if they are independent there are more chance that you can do both of them together than two parallel task being dependent. what say?

I'll play devils advocate, I think this would be possible with photographic memory and lots of buffer space, because books are just images stored on pages. Assuming your eyes are the input, you could take in each page or image in any order and absorb the concepts and relationships of the text in any order. This would end up being more like scattering a 1000 piece puzzel out on your kitchen table and without touching it put it together in your mind and describe the picture it represents. (no box picture for cheating) You can get a sense of this by reading the last paragraph of a book then read the second to last paragraph, then the 3rd to last paragraph and so on. If you are a speed reader you take in sections at a time much like looking at a photo. Expanding this idea to whole pages with advanced technology wouldn't be that far fetched in 25 years or so. Quantum computing would be the ultimate parallel computer that we know of. You should read The singularity is near by Ray Kurzweil

Having a little knowledge of brain functioning, I can say that the brain already parallel-processes billions of instructions per second to coordinate muscles, organ functions, hormones and other things without having to consciously think about them. That is why engineers have not been able to re-create that level of processing power in microchips.

And it would be difficult to harness that power to a process that requires serial processing. Words and letters do not come at the perso all at once, yet images seem to be processed all at once by some people. This may be a key to your idea.