Data


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Goals

  • To learn about the nature of digital information
  • To know the difference between analog and digital signals
  • To be familiar with data compression algorithms and why they are performed


Topics

transistor , bit , byte (kilo-, mega-, giga-, tera-), analog , digital , file , directory , folder , backup , data redundancy , American Standard Code for Information Interchange (ASCII), Unicode , standards

Read about

Numbers and Characters

Computers speak in the language of 0's and 1's, also known as the binary numbersystem. If you think about all the tasks we rely on computers to do today, there's quite a bit you can do with these two numbers. Bits and bytes represent units of data that can be processed by computers. One bit holds one number, which can be either 0 or 1. One byte holds 8 bits, or a series of eight 0's and/or 1's.

Since each bit can hold one of two values, a byte can therefore hold 2⁸ or 256 possible states. One byte can thus represent any integer number from 0 to 255. Two bytes can represent any integer from 0 to 65,535. Increasing aggregates of bytes (kilo-, mega-, giga-, tera-) can improve precision indefinitely, while adding information about the positive or negative sign of a number.

Calculations in the binary number system may be performed using Boolean logic . Physical implementation of Boolean logic can be performed by representing 0's and 1's with "high" and "low" voltages over wires, using electronic gates or relays . This is the idea behind computer "chips" which perform the complex data processing we expect from computers today.

Similarly, alpha-character data can be represented by sequences of 0's and 1's. The most common standards used for alpha-character data (regardless of font family) are ASCII (American Standard Code for Information Interchange) and Unicode .

A file, whether a word document or an image or a spreadsheet, is viewed in its simplest form by the computer as a sequence of binary data. Numbers, characters, images, sounds, etc. are all stored as a sequence of 0’s and 1’s. Files are stored in folders, also known as directories.

Images and Sounds

Images can be subdivided into very small points, which can then be represented as numbers assigned to colors within a predefined palette. Similar to a painting consisting of dots of color (Pointillism), the smaller and closer the dots are to one another, the better the resolution of the image will be. Numbers representing the color and intensity at each of these dots can be converted to binary code and transmitted to a receiving computer. The receiving computer then converts all of those numbers back to the image, which then appears on the screen. A Video Graphics Array (VGA) interface used in the old Cathode Ray Tube (CRT) monitors required the computer to convert the digital data to analog signals in order to display the image, while the newer digital interfaces such as Digital Visual Interface (DVI), High-Definition Multimedia Interface (HDMI), and DisplayPort allow the digital data to be transmitted directly to the LCD (liquid crystal display) panel without the conversion to analog, improving image quality.

What we hear as musicand voices speaking are sound waves causing physical movement in our eardrums. These waves are perceived in terms of pitch and volume by the brain. An absolutely pure tone looks like a sine wave . Compared to this, a person’s voice coughing, talking, or singing has a funny “lumpy and bumpy” shape. Given enough sampling, any wave can be represented by numbers that stand for the amplitude of the wave at each point in time. These numbers can then be sent between computers in binary format. The function of “sound cards” in computers is to turn analog information (e.g. a human voice saying “hello world”) to digital information during sound recording. They also perform the opposite function when computers play digital music files (i.e. found on CD, or mp3) over their speakers.

Analog vs. Digital Signals

Binary data is easily converted into analog or digital signals because it only has two states, 1 and 0. Over a wire in digital signaling , these two states can be represented by pulses of electricity or light, and be sent from one computer to another. The receiving computer can then decode the signal by transforming the binary code back into letters or numbers. Alternatively, a way of conveying binary information via analog signaling can be by frequency modulation (FM) or amplitude modulation (AM); these signals may be sent "wirelessly ." Other kinds of modulationcan be done to transmit sound over analog or digital networks.

Compression

If you can imagine sending a video that has both sound and images changing at multiple frames per second, the amount of data to be sent quickly becomes enormous. Compressionis a useful transformation of the data that reduces redundancies and eliminates certain unnecessary components (in lossy compression), thus creating a smaller data set that is sent more efficiently. Files may become compressed using programs like WinZip or Stuffit .

Activity

#1: Answer the following questions

  • What is the difference between a folder and a directory?
  • What is the difference between a technical standard and a natural standard (e.g. the speed of light)?

Online resources



Questions

Take the online quiz after going through the readings from this lesson.

Advanced courses


Expert corner

Help needed with Wikipedia article(s): computer file


Data | Goals | Topics | Read about | Activity | Online resources | Questions | Advanced courses | Expert corner
This page was last modified by - JRGilbertson JRGilbertson on Aug 10, 2009 4:27 am.