BITS AND BYTES

A BYTE is really not complicated at all. It is simply a group of eight BITS. When eight BITS are structured into a BYTE, then each of those BITS has special significance. You look puzzled! What, you say, is a BIT?

A BIT is the smallest piece of information that a computer can deal with. To help understand how BITS are used by the computer, it may help to imagine the microprocessor as a bus station. This bus station is on a single-lane road. That means a bus can only travel in one direction at a time as there is not enough room for two buses to pass each other. Therefore, a bus may either be arriving at the station or departing. The microprocessor, or bus station, can schedule its bus with a signal light that says "I am accepting arrivals" or "I am sending departures".

In fact, in real computer hardware architecture, the wires that carry information to and from a microprocessor are called the DATA BUS. We don't need eight separate INPUT and eight separate OUTPUT wires because, like the single lane road connected to the bus station, the wires are bi-directional. In other words, information can either be arriving (INPUT) or departing (OUTPUT), but not both. The microprocessor also has a signal of its own that determines whether it will receive (INPUT) or send (OUTPUT) information.

Let's take a closer look at that bus. It is known as the BYTE express, has eight seats, and always carries eight passengers. Those passengers are little messengers known as BITs, and, as a group, they are known as a BYTE. These messengers, or BITs, are rather moody. They are either turned "ON" or they are turned "OFF." That is called BINARY as they are BI-STATE signals, ON being a "1" state and OFF being a "0" state. Their vocabulary is just as limited... the only thing they are willing to tell you is their mood. Now how do we get any meaningful information out of a group of eight little messengers standing in front of us, each screaming "ON" or "OFF" at one time?

Well, when the bus arrives, we could have the whole BYTE stand in front of us and then count everyone who is turned "ON." That would give us the capability of counting to eight. Seems pretty limited, doesn't it? Hmmm, the group really needs a leader. That leader will be the first BIT on the left. We'll call that BIT the Most Significant Bit, or the MSB. The last BIT on the right will be the Least Significant Bit, or LSB. Terrific! Now that we have a group leader and a group follower, all the BITs should be given a rank.

Handing out ranks is serious business and much thought should be given to it. We can start with the LSB and assign that BIT the rank of "1," since it is the Least Significant Bit. We can be easy on everyone if we just double that rank for the next BIT in line. So, why not just keep doubling the rank for the next BIT in line and so on until we get to the MSB or Most Significant Bit. Now our BYTE looks something like this:

What have we gained? More than meets the eye! When the BYTE gets off the BYTE express and each BIT starts telling us what its current mood is, we can make a different and more meaningful interpretation out of the little guys. If everyone is turned "OFF" except the fourth BIT from the right, for example, we can check the rank of that BIT and find it is eight (8). Unknown to the BITs, they have brought us a message and the message is "8".

Aha, what if we want the bits to get on the bus and carry a message that says "9". This is a problem because there is no bit with a rank (value) of 9. What to do? I guess the next best thing is to be very nice to the bits that have values of one and eight and turn them both on. When we look at the BYTE now we see 1 + 8 which gives us our 9. Easy. Even my student Nerdwell can count that high. In fact, Nerdwell can count to 255 because if you add up all the values of the bits, you get 255:

1 + 2 + 4 + 8 + 16 + 32 + 64 + 128 = 255

Return to Table of Contents | Previous Chapter | Next Chapter