1.1.2 Data Processing
A computer is a data processing machine.Data flow into the machine as input.Information flows from the machine asoutput. The computer processes the data.Johannes Kepler spent twenty years of hislife processing data. Today, a college
student using a computer can repeat hiscomputations in a few hours.
What do we mean when we say that a computerprocesses data? We process iron ore to makesteel; we process wood pulp to make paper."Process" implies that a change takes place, andthat the raw materials are in some way
restructured or manipulated. Often, data
processing involves filtering and summarizingdata so that underlying patterns can be perceived.How does a computer process its data? Whatfunctions, what operations, can it perform?
Generally, computers can add, subtract, multiply,divide, compare, copy, request input, and requestoutput. So can most pocket calculators.Whatmakes a computer different?
1.1.3 The Stored Program Concept
To add two numbers on a calculator, you:
1.Enter the first number.
2. Press the add button.
3. Enter the second number.4. Press the result button.
5. Record the sum for future reference.The calculator finds the sum, but you must
provide control by deciding what button to pushnext. A calculator requires direct human
intervention at each step.
A computer processes data automatically,withouthuman intervention. Computers are not intelligent,however. They don't know when to add, or subtract,or compare, or request input. If a computer is to
function without direct human control, it must begiven a set of instructions to guide it, step by step,through a process. The set of instructions is called aprogram. The program is stored physically insidethe machine, making it a stored program.The storedprogram distinguishes a computer from a calculatorand allows it to function without human intervention.Let's incorporate this idea into our definition:
Computer: A machine that processes data intoinformation under the control of a stored program.
1.2A computer System1.2.1 System Components
A computer system consists of several basiccomponents. An input device provides data. Thedata are stored in memory,which also holds aprogram. Under control of that program thecomputer's processor manipulates the data,storing the results back into memory. Finally, theresults flow from the computer to an output
device.
Additionally, most modern computers use
secondary storage to extend memory capacity.Let us think of a computer system. The keyboardis an input device. Above the keyboard is an
output device, the display screen. The imagedisplayed on a screen is temporary; a more
permanent copy of the output can be obtained bysending it to a printer. The computer's processorand main memory are located in the small cabinetnear the center of the system. The diskette drivesin the front of the cabinet extend the computer'smemory; programs often enter the system throughsuch secondary storage devices.