"Information" is one of the great buzz words of the last half century. The term has been in use in the English language for centuries, but it started to be used in its present technical sense in 1948, when a brilliant communications engineer working for the phone company named Claude Shannon ushered in the field of inquiry now known as Information Theory. He formalized the use of the term, and made it mathematically quantifiable. He thought of information as sequences of bits, or ones and zeros.
Claude Shannon was not a philosopher, he was an engineer. He mathematicized information so that he could calculate, for example, that a communications channel capable of transmitting X bits per second with an error rate of up to Y bits per 1000 could be used to transmit Z bits per second error-free (where Z is somewhat smaller than X), given some sort of transformation of the information on either end of the communications channel. He was concerned with noise on the wire. He was concerned with characterizing the "information density" in a given stream of bits so that by compressing the stream (i.e. increasing the information density) one could effectively transmit the same amount of information using fewer bits and therefore less bandwidth on the communications channel, thereby saving the phone company money. Essentially, Shannon was interested in very practical, meat-and-potatoes sorts of questions. Others, however, have not been so conservative. Information theory has inspired many philosophers to make extremely extravagant claims. Information has become one of the most popular reductive bases in the reductionist's toolkit. That is, just about everything at one time or another has been argued to be really just information, or information processing.
Of particular interest with regard to these essays, of course, mind and consciousness are very commonly thought to be really just information and/or information processing. Indeed, the entire cognitive science program is predicated on the notion that the brain is (just) a complicated information processor - that not only can it be seen in terms of information processing, but that seeing it in these terms captures what is interesting about the brain in its entirety. The brain is nothing but a big information processor; any similarly configured information processor of equal capacity would manifest a mind in every sense that the brain itself manifests one. These sound like rather large and sweeping claims, but we can not even know whether they are or not (let alone whether or not they are true) until we nail down exactly what is meant by "information" and "information processing".
In what sense does an information processor actually process information? Does it manipulate symbols? These sound like silly questions at first, but their answers depend on how exactly you define "information" and "symbol". In spite of the well developed field of Information Theory, it is devilishly hard to find anyone who commits an actual definition of the term "information" to print. While people who are interested in qualia and the Hard Problem may not have answered the corresponding questions for the term "qualia", they acknowledge at least that there is work to be done along these lines. People on both sides of the Hard Problem debate, however, too easily assume that we know what we are talking about when we speak of information and information processing. Information is more difficult to pin down than is generally accepted, and there are very different things that are meant by the term depending on the context.
There are molecules of ink on a page made of more molecules; there are perturbations in a physical electrical field on a metal wire; there are photons of light which propagate through an optic fiber. When I look inside a computer, I see voltage levels, and diodes which behave differently when subjected to different voltage levels. All of these things (or collections or patterns thereof) may be seen as information, but the key phrase there is "may be seen".
Information theory is a branch of mathematics, and bits, like lines and points in Euclidean geometry, don't really exist, at least not out there in the real world. They are Platonic abstractions. We may profitably see things that are really there (like voltage levels) as information, and make generalizations, and hence predictions about those voltage levels based on our analysis, but the predictions we come up with will never be anything that we could not have, in principle have derived from a sufficiently detailed knowledge of the physical system alone without reference to any notion of "information". Information is an abstraction, and abstractions, to a physicalist, must be cashed out in terms of the nuts and bolts that make up the actual physical universe. In practice, it may be very difficult for us to make useful predictions about an information processing system at the level of raw physics, but the point is that the universe itself has all it needs to clank along, one moment to the next, without our notions or theories of "information". Put differently, once God had established all the physical facts of the universe (i.e. the physical laws and initial conditions) He did not have to do any additional work to determine the facts about information. Everything the universe needed with regard to information flows and processing was already baked in.
When you have a system before you that supposedly processes information, what you really have is a collection of molecules, obeying the laws of physics that pertain to such collections of molecules. It is not merely the case that the information needs a substrate to instantiate it - the information just is the physical substrate, just as heat just is the mean kinetic energy of a collection of molecules. The purported causal efficacy of a 0 or a 1 in a computer circuit is entirely due to the voltage level on the wire and the physical laws that apply to such voltage levels, and there isn't a shred of efficacy imparted by any so-called informational content above and beyond this. The system may be seen as informational, and we may thereby derive interesting and important conclusions, but these conclusions will themselves be may-be-seen-as conclusions, couched in terms of the abstractions of information theory.
In short, information in the real world always really consists of physical things. What makes some physical things information and others not? It might be tempting at this point to turn from the strictly syntactic notions of information theory to a more semantic characterization of information. We might say that information represents something. What does this mean (without circular reference to information)? Does the light from distant stars, striking an earthly telescope, constitute information about the stars? If so, does any physical effect of any other physical thing constitute information about that thing? Do all effects represent their causes, simply by virtue of the fact that someone might potentially be able to infer the cause (or something about the cause) just by observing the effect?
We might then start by saying that thing1 represents thing2 if thing1 is caused by thing2, or if thing1 varies in regular, lawlike ways as a function of variations in thing2. But this seems too broad. Since from the time of the Big Bang, each particle in the universe has some influence on every other particle (from the non-zero gravitational influence that any two objects of non-zero mass exert upon each other, if no other), everything is caught up in the causal mesh - everything behaves just the way it does as a function of everything else. If information is anything which is caused by other things in lawful, regular ways, then everything is information. In fact, everything is information about everything else. If everything is information about everything, then the term is nearly useless, and should be replaced, in philosophical debates, with the more honest term "stuff". And "information processing" could be reasonably be replaced with the term "stuff doing stuff because of the influence of other stuff".
But when people invoke the term "information" to describe some physical stuff interacting with other physical stuff, they are not usually talking about the stuff itself as such. Information is necessarily abstract. It is not the voltage levels or the ink, but the pattern of voltage levels or ink. It is sometimes said that information is a difference that makes a difference. But as Rosenberg has pointed out (1998), the informational content of anything, whether ink on a page or electrical impulses on a wire, is a bare schema, or a pattern of bare differences. That is to say, the differences by virtue of which something is considered to be information are differences that are circularly defined in terms of each other. What is 0? It is not 1. What is 1? It is not 0. And this is all you ever need to know, all there is to know, about 0 and 1. 0 and 1 can be manifested, or carried, by any physical medium capable of assuming two distinguishable states (voltage levels on a wire, water pressures in a hydraulic system, wavelengths of light on an optic fiber). One of information's distinguishing characteristics is that it is independent of its particular carrier. Information is arbitrarily transposable. Information must be carried or manifested by a physical substrate whose nature outruns the simple criterion of mere distinguishability of states necessary to carry, represent, or manifest the abstract 0s and 1s of the information itself.
Given any system, an informational explanation of its behavior is reducible to a physical explanation of its behavior, at least in principle. But as I (and others) have argued, this is not true of qualia. Subjective consciousness is not reducible to physics. Qualia thus are not themselves information, although they can carry information. Red can mean "stop!", even though red itself is not information. Red can only be what it is, absolutely. It is not simply the case that some event or process in my brain may be seen as my seeing red. Redness is a qualitative essence and can not survive any transformation or translation into anything but redness. Unlike information, qualia are not transposable at all.