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History-of-Computers Powered By Docstoc
					History of Computers

Throughout time, humans have invented ingenious calculating machines. One of the
earliest was the abacus. It's about 5,000 years old. Mechanical calculators that could add
and multiply (but not subtract!) were invented in the 1600s. In 1820, Charles Xavier
Thomas de Colman invented the arithometer, a machine that could add, subtract, multiply
and divide. It was Charles Babbage though, in the early 1800s, who designed mechanical
calculating machines (see photo) that were the true ancestor of today's computers. Ada
Byron King (Countess of Lovelace) was his programmer and today is considered the
mother of computer programming.

Babbage's design for his ultimate calculator, the Analytical Engine, was never produced.
It did anticipate the four components essential to modern computing. These components
are input, storage, processing and output.

The problem with Babbage's and other mechanical calculators was just that—they were
mechanical. The moving parts they relied on were slow and subject to breakdown.
What made modern computers possible was the invention of something that could do
calculations and other information processing with no moving parts and do it very fast.
That something was electronic components. With electronic components, a fast and
efficient machine such as Babbage proposed could be built with all four components
essential to modern computing.

Four Components of a Computer
A computer processes information. A toaster processes bread. Although it's a simpler
device, a toaster is a good way to demonstrate the four components of computer
processing: input, storage, processing, and output.
Both a toaster and a computer have physical parts you can touch such as the keyboard
and mouse. We call these parts hardware.
Here the similarities between toaster and computer end and the differences begin. Only
the computer has something called software that enables it to figure out what to do with
the input you give it. You can't touch software. Software that gives the computer the
ability to process many kinds of information. In contract, all a toaster can process is bread
(and the occasional waffle).

Another difference is a computer has a microprocessor. The microprocessor is the device
in the computer that performs most of the tasks we ask the computer to do—from playing
computer games to graphing the number of people who prefer cricket to curling. The
microprocessor reads and performs different tasks according to the software that instructs
it. This ability is what makes the computer such a versatile machine.

The key thing to remember is this: both computer and toaster have four basic components
to how they operate (input, storage, processing, and output.) Unlike the toaster, the
computer is unlimited in the things it can do.
Computers are information processing machines. That means that you can use them to
access and change information like numbers, text, pictures, and even music. Think of
what you can do to modify a single sentence. Using the computer, it's easy to add, delete,
or rearrange words. To change a sentence with your computer, though, first you have to
get the sentence into your computer.

Input devices are used to put information in your computer. You type a sentence on your
keyboard and it goes into the computer. You speak into a microphone and your computer
records your words. You make funny faces at the video camera and your computer
records every one of them. Even the mouse you are about to click to move on to the next
section is an input device. So, when you are ready, click it!

How Computers Store Information
When you use a telephone, it does not store information. You speak into the phone, the
person on the other end hears what you say and then your words are gone. An answering
machine is different. It answers the phone and stores the information given by the caller.

To process information, computers need to be able to store it. Otherwise, like the phone,
information would come and go before anything could be done with it.

Computers store all kinds of information. They store the information you give them,
instructions from the software you're using, plus the instructions they need to operate. To
store all this, they use two basic kinds of storage. Temporary storage is for information
actively being used for processing. Random Access Memory (RAM) accepts new
infomation for temporary storage. Long-term storage is for information computers use
again and again, such as the instructions the computer prepares itself with every time you
turn it on. These instructions are stored in read only memory (ROM), a type of memory
that does not accept new information.

Computers also use a variety of devices to store information that isn't actively being used
for processing. Hard drives, CD or DVD storage, and floppy disk drives
Computers use Random Access Memory for the information they currently need to do a
task. Parts of the program you are currently using and the data you are manipulating are
held in RAM while you are working with them. But what about the rest of the programs
and information on your computer? They are stored in a variety of other media. You are
probably familiar with many of the ones shown on this page. What you might not know is
the amazing amount of information some of these can hold.

How Computers Process Information
Computers use integrated circuits to process information. Of the many chips in a
computer, the microprocessor is the most complex. It is where the information you give a
computer is processed. It is sometimes referred to as the brain of the computer.
A simpler kind of chip is used to make DVD players, remote controls, and electronic
calculators. They're made to do one thing well and the instructions are coded into them.
You can't install new software to change what they do. For example, you can't do word
processing on your VCR.
The Microprocessors found in computers are much more versatile. Change the software
you're using and you can go from doing word processing to playing a computer game.
Change the software again and you can explore the Internet. Instead of being designed to
do one thing, microprocessors are designed to do whatever the software you select
instructs them to do.

How Computers Deliver Information
All the processing power in the world wouldn't matter much if you couldn't get output
from a computer. You're looking at output right now on your screen. You told the
computer you wanted to view this page and the software and microprocessor inside it
responded by putting the page on your monitor.

Other kinds of output include sound from your computer's speakers and documents
printed by your printer. Output can also include things like MP3 files. They allow you to
download music from the Internet onto an MP3 player you can take with you anywhere.

Computers are sometimes called electronic brains. But are they really brains? Let's compare.
First, let's look at how brains and computers work. A brain uses special cells called neurons that work
together to process electronic information and respond with an action. A computer uses a collection of
circuits called a microprocessor. One is living cells, the other is electronic circuits. Computers circuits
process electronic information called binary code.

What Is Binary Code?
People use all kinds of symbols, sounds, colors and body
motions to express themselves. These expressions are, in a
sense, codes—signals we use to communicate with one
another. Our brains fire electronic impulses thru our neurons
to communicate this code to and from our body.

Computers use a special code of their own to express the
electronic or digital information they process. It's called the binary code because it
consists of only two symbols—0s and 1s. (The "bi" in "binary" means two.)
Can you think of an object name consisting of the letters “BI”.

Why 0s and 1s? Because those are the only two numbers you need to express the flow of
electricity through a transistor. It's either on or it's off. On is 1, off is 0. Everything you
say to a computer has to be put in terms of these two numbers.

For a computer to execute or respond to a command, it has to be translated into the only
language a computer knows: the 0s and 1s of the binary number system. The 0s and 1s
represent the on and off of the transistors.

What do you call one of these 0s or 1s? A bit. Which makes sense when you see how
many of these bits it takes to represent a word, number, color, graphic or sound. They
really are just a "bit" of something bigger
    Imagine 8 on/off switches grouped inside the computer. Each switch(0/1) is called a
bit. It takes 8 bits to store one character (letter, symbol, or space). As shown below,
09090099 is the way the computer understands the letter S.

   0        1       0        1        0        0        1         1       =   the letter:   S

A combination of 8 switches is called a byte in computer terminology. The computer
groups 8 bits together to form a byte because it has proved to be a good combination for
the computer to handle. By using 8 bits to turn on various switches on and off, there are
256 different combinations possible. What is the math used to reach that number?
Each time a keyboard is struck, a binary number is generated in the computer via
electronic signaling. Inside the computer, the number is stored into memory. All data in
a computer is represented by the use of binary numbers.
We have now learned that the processor and memory (both ROM and RAM) are made up
of electronic circuits that represent information by turning switches off and on. And we
learned that eight switches or bits make up a byte and each byte can store one character
of data. Computer memory is measured in bytes, and groups of bytes are represented by
the terms below.

                                   Measuring Memory

         Term/Byte      Abbreviation      Value
         Kilo           K, KB             1,024 bytes
         Mega           M, MB, Meg        1,048,576 bytes (Million)
         Giga           G, GB, Giga       1,073,741,824 bytes (Billion)
         Tera           T, TB, Tera       1,099,511,628,000 bytes (Trillion)

How Computers Work With Pictures
Picture this. A computer is made up of millions of electronic switches (transistors).
They're either on or off, open or closed.

Now picture this. Your computer screen has hundreds of thousands of dots arranged in
rows and columns. Each dot is a picture element or pixel. Each of these pixels displays
some combination of red/green/blue according a device called a Video Graphic Array
(VGA) The VGA translates binary-coded information (0s and 1s) into the color
combinations required to make up an image on your computer screen.

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