The tiny, miniscule Bit . . . it's either a 1 or a 0. The bit is the only unit of information that a computer can work with. That's all there is, and there is nothing more. Every letter & digit . . . every picture & document . . . every video & audio clip, email, instant message, etc. etc. etc. They are all composed of bits. How wonderfully simple !!
And that is how inventors were able to build the incredibly complex computer - because the basic building block, the bit, is so simple. In the same way that the cells in our bodies are composed of atoms - the data structures in computers are composed of bits. Unfortunately, we humans aren't used to seeing the world as 1's and 0's and we aren't used to counting with that numbering system either, which is called binary, or Base-2. We use decimal, or Base-10.
Bits (0=OFF 1=ON)
You may think, why couldn't they have designed computers to understand 2,3,4, etc.? Well, they could have, but the problem was in the electronics. They found that transistors (and there are millions of them in computers), work best and reliably with just two electrical voltage states. That would be where one state is no electrical voltage, and the other state is positive voltage (3 volts, 5 volts, etc.). Think of a "0" as no voltage (a flashlight that has been turned OFF) and a "1" as the presence of voltage (a flashlight that has been turned ON). Hence, "O" is often call OFF, and "1" is often called ON.
History of the Binary Evolution and Computers
Incredibly, all those programs you use, all the colors and text that flash by on your screen, all those Internet websites . . . it is all comprised of 1's and 0's - all of it. Each 1 and each 0 is called a "bit", as in a "bit of information". So, a bit can have two states, it can be a zero or a one. And within the electronics of your PC, that would be delivered as a voltage, or a lack of voltage on one microscopic lead of a transistor.
Obviously, a bit is not much information, and in the early day of computing, the almighty "byte" was developed - which is simply equal to 8 bits. Later, multiple bytes were combined and called a "Word". However, still even today, the most commonly referred to units of info on a computer is bits and bytes.
By the way, there is another reason that computers work best by juggling units that have only 2 possible states. It is easy to deal with! When a part of a system knows that what is coming down the pike will be a 0 or maybe a 1, that small part of the whole system doesn't have to do a lot of thinking . . . and when you don't have to do a lot of thinking . . . you're fast.
This concept of small, simple units = fast speed, will come up again in the Telecom section of Frame Relay and ATM.
Nibble - an uncommon term, but if you run across it, it is (as can be expected) a small sized byte. Actually, it is one-half of a byte, or 4 bits