Computers perform many useful tasks by accepting data as input, processing it, and releasing it as output. Data is information. It can be a set of numbers, a memo, an arrow key that moves a game symbol, or anything you can image.
The computer translates input into electrical signals that move through a set of electronic controls. Output can be though of in four ways:
- As characters the computer displays on screen.
- As signals the computer holds in memory.
- As codes stored magnetically on disk.
- As permanent images and graphics printed on paper.
Computers receive and send output in the form of electrical signals. These signals are stable in two states: on and off. Think of these states as you would electricity to a light switch that you can turn on and off. Computers contain millions of electronic switches that can be either on or off. All input and output follows this two-state principle.
Binary, the computer name for two-state principle consists of signals that make up true computer language. Computers interpret data as two binary digits - or bits - 0 and 1. For convenience, computers group eight bits together. This eight-bit grouping or byte is sometimes package in two-, four-, or eight-byte packages when the computer moves information internally.
Computers move bits and bytes across electrical highways called buses. Normally, the computer contains three buses: the control bus, the data bus, and the address bus. The microprocessor connectors to all three buses and supervises their activity. The CPU uses the data bus to determine what the data should be, the control bus to confirm how the electrical operations should proceed, and the address bus to determine where the data is to be positioned in memory.
Because the microprocessor can call on this memory at any address and in any order, it is called random-access memory, or RAM. The CPU reads and activates program instructions held in RAM. Resulting computations are stored in RAm.
Some computer information is permanent. This permanent memory called read-only memory (or ROM) is useful for holding unalterable instructions in the computer system.
What Is Information?
It is neccessary to explore what information is before we can understand how computers uses information in data processing.
Information can be defined in terms of its characterisitics:
- Information is objective. Mathematics and science champion the concept of objective information. This may be true in an abstract formalized setting. It is often not true in the real world.
- Information is subjective. What is information for me may not be information for you. Who decides what is and what is not information?
- Information is temporal. What was not information in the past might become information in the future. In contrast, what was information in the past might not be information in the future.
- Information is ephemeral. Information might have value at one time and never again.
- Information is not fungible. Information does not have identical interchangeable parts.
- Information is not reduced by giving it away.
- Information is not always additive. Twenty books on the same subject do not provide twenty times as much information.
- Information is both a process and a commodity. At this moment your body is processing thermal, tactile, audio, and visual information about your enviornment. At this moment somewhere, information is also being bought and sold.
- Information is measurable and not measurable.
Each 0 or 1 is called a bit. Bit is an abbreviation of the expression BInary digiT. It is called binary, since it is derived from
the binary number system:
The binary number system
The binary number system is made up of digits, just like our common decimalsystem (10 digit system). But, while the
decimal system uses digits 0 through 9, the binary system only uses digits 0 and 1.
If you are interested in understanding the binary number system, then here is a brief course. Try if you can follow the
system. See how numbers are constructed in the binary system, using only 0's and 1's
We have seen that the PC appears capable of handling data, if it can receive them as 0's and 1's. This data format is
called digital. If we can translate our daily data from their analog format to digital format, they will appear as chains of 0's and 1's, then the PC can handle them. So, we must be able to digitize our data. Pour text, sounds, and pictures into a funnel, from where they emerge as 0's
Let us see how this can be accomplished.
The most basic data processing is word processing. Let us use that as an example. When we do word processing, we
work at a keyboard similar to a typewriter. There are 101 keys, where we find the entire alphabet A, B, C, etc.
find the digits from 0 to 9 and all the other characters we need:,.-;():_?!"#*%&etc..
All these characters must be digitized. They must be expressed in 0's and 1's. Bits are organized in groups of 8. A group of 8 bits is called a byte.
8 bits = 1 byte, that is the system. Then, what can we do with bytes? First, let us see how many different bytes we can
construct. A byte is an 8 digit number. We link 0's and 1's in a pattern. How many different ones can we make? Here is
one: 01110101, and here is another: 10010101.
We can calculate that you can make 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 different patterns, since each of the 8 bits can have 2
(two in the power of eight) is 256. Then there are 256 different bytes!
Now we assign a byte to each letter and other characters. And since we have 256 patterns to choose from, there is
plenty of room for all. Here you see some examples of the "translation:"
When you write the word "summer", you write 6 letters. If the computer has to process that word, it will be digitized to 6 bytes. In other words, the word summer occupies 6 bytes in the PC RAM, when you type it, and 6 bytes on the hard
disk, if you save it.
ASCII is an acronym that means American Standard Code for Information Interchange. It is an industry standard, which assigns letters,
numbers, and other characters within the 256 slots available in the 8 bit code.
The ASCII table is divided in 3 sections:
?Non printable system codes between 0 and 31.
"Lower ASCII" between 32 and 127. This part of the table originates from older, American ADP systems, which
work d on 7 bit character tables. Foreign letters, like Ø and Ü were not available then.
? "Higher ASCII" between 128 and 255. This part is programmable, in that you can exchange characters, based on
which language you want to write in. Foreign letters are placed in this part.
Let us imagine a stream of bits sent from the keyboard to the computer. When you type, streams of 8 bits are sent to the
us look at a series of bits:
Bits are combined into bytes (each 8 bits). These 24 bits are interpreted as three bytes. Let us read them as bytes:
00110010, and 00110011.
When we convert these byte binary numbers to decimal numbers, you will see that they read as 49, 50, and 51 in
decimal numbers. To
interpret these numbers, we have to look at the ASCII table. You will find that you have typed the numbers 1, 2, and 3.
About text and code
Now we have seen the PC's user data, which are always digitized. But there are many different kinds of data in the PC.
You can differentiate between 2 fundamental types of data:
? Program code, which are data, that allow the PC to function.
? User data, like text, graphics, sound.
The fact is, that the CPU must have instructions to function.. An instruction is a string of data, of 0's and 1's. The CPU is designed to recognize these instructions, which
arrive together with the user input data to be processed.
The program code is thus a collection of instructions, which are executed one by one, when the program runs. Each
time you click the mouse, or hit a key on the keyboard, instructions are sent from your software (program) to the CPU,
telling it what to do next.
User data are those data, which tells the software how to respond. The letters, illustrations, home pages, etc., which you
and I produce, are created with appropriate software.
Both program code and user data are saved as files on the hard disk. Often, you can recognize the type of file by its suffix.
Here are some examples:
This is written as an introduction to naming files. The file name suffix determines how the PC will handle the file.