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Chapter 2 Understanding the Digital Domain

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  1. Chapter 2Understanding the Digital Domain Information Technology in Theory By Pelin Aksoy and Laura DeNardis

  2. Objectives • Understand the difference between analog and digital representations of information • Learn about techniques for transmitting and storing digital information • Understand the use of multipliers for representing, transmitting, and storing large amounts of digital information • Discuss the advantages of representing information in digital format and using digital devices for processing, exchanging, and storing information Information Technology in Theory

  3. Emergence of the Digital Age • “Digital information” refers to representations of numbers, text, sound, and images as a combination of two fundamental logic symbols: 1 and 0 • These symbols are also called binary symbols, binary digits, or bits • Digital devices process information in the form of ones and zeros; in other words, they speak a binary language Information Technology in Theory

  4. Emergence of the Digital Age (continued) • People recognized the possibilities of digital technology • They began to develop digital devices that could “speak” the binary language advancement • To realize this, an efficient switch was needed • Vacuum tube • Transistor • Integrated circuit Information Technology in Theory

  5. Emergence of the Digital Age (continued) Information Technology in Theory

  6. Emergence of the Digital Age (continued) An integrated circuit Information Technology in Theory

  7. Emergence of the Digital Age (continued) • Moore’s Law states that “The number of devices that can be integrated on a chip doubles every 18 months” • Current technology indicates that Moore’s Law will reach its limit in the future, so research on alternative technologies is underway • Digital technology has evolved tremendously over the past few decades and will continue to evolve Information Technology in Theory

  8. Analog Information • Digital devices process many forms of information in combinations of bits • Most information we encounter is analog, not in terms of 1s and 0s • When we speak, we exchange information in analog format; what we hear varies proportionally, or analogously, to the sound produced by the person who is speaking • We call this analog information Information Technology in Theory

  9. Analog Information (continued) • A speedometer example helps to understand the difference between analog and digital • The speed varies continuously and an infinite number of speed values exist over a given time measurement • Information produced by the speedometer is analog information • The speedometer is classified as an analog device Information Technology in Theory

  10. Analog Information (continued) Information Technology in Theory

  11. Analog Information (continued) • It is desirable to digitize analog information using analog-to-digital converters • First task to digitize is to reduce infinite number of speed measurements to a finite number • In other terms, make the information discrete • Reducing infinite number of speed measurements corresponds to sampling each measurement Information Technology in Theory

  12. Analog Information (continued) Information Technology in Theory

  13. Analog Information (continued) • The next task is to round the speed values to the closest speed value available • Finally the rounded-off speed values are assigned a binary code • A speedometer that is able to display digital speed values is classified as a digital device • Can you name other digital devices? Information Technology in Theory

  14. Analog Information (continued) Information Technology in Theory

  15. Analog Information (continued) • To convert any form of analog information to digital, the analog information should first be reduced to a finite set of values • Each value should be rounded off • Each rounded-off value should then be assigned an appropriate binary code Information Technology in Theory

  16. Manipulating Bits • Speedometer example conveyed how bits can logically represent information • How can bits be physically generated so as to transmit and store digital information? • Bits may be physically generated using electrical energy, magnetic energy, or electromagnetic energy • A signal is used to transport bits physically across a transmission medium Information Technology in Theory

  17. Manipulating Bits (continued) • Examples of signals include: • Electrical signals • Magnetic signals • Optical signals • Sound signals • Radio frequency signals • Etc. • Examples of transmission media include metallic wires, fiber-optic cables (i.e. optical fibers), air, etc. Information Technology in Theory

  18. Manipulating Bits (continued) • Bits should always exist physically in a form that is based on the type of transmission media to be used • If using fiber-optic cables, bits should be sent out as optical signals • If using metallic wires, bits should be sent out as electrical signals, etc. Information Technology in Theory

  19. Manipulating Bits (continued) Information Technology in Theory

  20. Data Rate • Rate at which bits are sent out over a transmission medium • Measured in terms of bits per second (bps) and bit period in terms of seconds • Data rate=1/bit period • More complex version of this expression is explained in a later chapter • If bit period is 1 second, then data rate is 1 bps Information Technology in Theory

  21. Data Rate (continued) • Large and small numbers are usually expressed more compactly through the use of multipliers • Multipliers commonly used in the IT world within the context of transmission: • Kilobits per second (Kbps) 103 = 1000 bps (thousand) • Megabits per second (Mbps) 106 = 1,000,000 bps (million) • Gigabits per second (Gbps) 109 = 1,000,000,000 bps (billion) • Terabits per second (Tbps) 1012 = 1,000,000,000,000 bps (trillion) Information Technology in Theory

  22. Data Rate (continued) • Solve some examples: • Calculate how many bits per second are transmitted over a 384-Kbps cable modem connection • Calculate how many bits per second are transmitted over a 1.25-Gbps fiber optic connection Information Technology in Theory

  23. Storing Bits • Storage media store digital information in some physical form • Most forms of storage media traditionally fall into one of the following categories: • Mechanical storage • Magnetic storage • Optical storage • Magneto-optical storage • Electronic storage Information Technology in Theory

  24. Storing Bits (continued) • Examples of current and historical storage media include: • CDs • DVDs • Hard disks • Floppy disks • Flash memory • Punch cards • Can you identify which media are mechanical, magnetic, optical, and electronic? Information Technology in Theory

  25. Mathematics of Storage • Digital information is stored by grouping bits into bytes • 8 bits = 1 byte • Multipliers are commonly used in the IT world within the context of storage: • Kilobyte (KB) 210 = 1,024 bytes • Megabyte (MB) 220 = 1,048,576 bytes • Gigabyte (GB) 230 = 1,073,741,824 bytes • Terabyte (TB) 240 = 1,099,511,627,776 bytes Information Technology in Theory

  26. Mathematics of Storage (continued) • Some examples: • Calculate the storage capacity (the number of bits) that can be stored on a 700-MB CD • Calculate the number of bits in a 68-KB digital file stored on your hard disk Information Technology in Theory

  27. Advantages of Digital Technology • Ability for noise removal • Capacity for error control • High speed • High level of security • Amenable to compression • Reliable storage of information • Ease of reproduction • Simplicity in transmission Information Technology in Theory

  28. Ability for Noise Removal • Noise is defined as an effect that disrupts a signal, hence the information carried by the signal • Noise acts upon both analog and digital signals • It is desirable to remove noise in its entirety from the signal • It is always easier to remove noise from digital signals than it is from analog signals • Threshold device may be used to remove noise from a noisy digital signal Information Technology in Theory

  29. Ability for Noise Removal (continued) Noisy analog signal Information Technology in Theory

  30. Ability for Noise Removal (continued) Noisy digital signal Information Technology in Theory

  31. Ability for Noise Removal (continued) Information Technology in Theory

  32. Capacity for Error Control • Not all levels of noise may be removed from a noisy digital signal • If noise levels are too great, a receiver might make an incorrect decision on the value of the bit, resulting in an error • Special error control schemes may be used to detect and sometimes correct errors if they occur at the receiving end of a communications system Information Technology in Theory

  33. Capacity for Error Control (continued) • Error control is accomplished by applying extra bits prior to transmission at the transmitting end • These redundant bits help the receiver in detecting/correcting errors if they occur • Errors are not only limited to transmission systems • They also frequently arise within storage systems • Similar error control schemes may be applied prior to storage so that the reading device may be able to detect/correct errors Information Technology in Theory

  34. High Speed • Digital information may be transmitted and processed faster than analog information • Improved transmission media materials and special transmission techniques enable faster transmission speeds • Miniaturization of transistors, the development of novel materials, and more refined manufacturing techniques for integrated circuits enable faster processing Information Technology in Theory

  35. High Level of Security • Digital systems can protect sensitive information by encrypting information • Encryption ensures that if third parties intercept information-carrying signals, they cannot decipher the signals • One encryption method is to reverse the order of the bits before transmission; for example, a bit stream of 1100 is transmitted as 0011 • As long as the transmitting and receiving ends agree on the scheme, the receiver can decipher the information Information Technology in Theory

  36. Amenability to Compression • Digital information is highly amenable to compression (a reduction in the overall number of bits to be transmitted/stored) • This is especially true for digital audio, image, and video files • Applying compression algorithms can help to achieve various levels of compression • Both lossy and lossless compression schemes exist in IT Information Technology in Theory

  37. Reliable Storage of Information • Analog storage approaches are highly amenable to degradation during storage • If an analog audio cassette is played repeatedly, the overall quality of the audio stored on the cassette is reduced • In contrast, digital storage approaches such as CDs and flash drives can store information more reliably over long periods of time Information Technology in Theory

  38. Ease of Reproduction • Analog information is highly susceptible to degradation during reproduction • An analog audio cassette tape copied in a double cassette recorder usually does not have the same quality as the original tape • Information on digital media such as flash drives can be reproduced with the same quality as the original, and with greater ease Information Technology in Theory

  39. Simplicity in Transmission • Digital information is easy to transmit, because the transmitter needs to generate a signal with only a discrete number of values • Consequently, the receiver needs to follow a signal with only discrete number of values • Transmitters that have to transmit analog signals must be able to generate a signal with an infinite number of values, and the receiver has to follow this complex signal Information Technology in Theory

  40. Summary • Digital devices are technologies that process information in the form of 1s and 0s • Digital information is discrete, comprising a finite number of information values • Analog information is continuous, comprising an infinite number of values • The transistor and the integrated circuit—a layer of silicon containing numerous interconnected transistors—were major breakthroughs that led to smaller and faster digital technologies Information Technology in Theory

  41. Summary (continued) • Moore’s Law states that the number of transistors contained on an integrated circuit doubles every 18 months • Any form of information, including sound, text, or images, can be represented digitally using ones and zeros • The bits can be physically generated using various sources of energy, such as electricity, light, or radio frequency • The rate at which bits are transmitted over any medium is called the data rate Information Technology in Theory

  42. Summary (continued) • Bits are usually stored on magnetic media such as hard disks, on optical media such as CDs and DVDs, on magneto-optical media such as magneto-optical drives, and on electronic media such as flash cards • Digital technology has many advantages over analog technology, including resistance to noise, higher speeds, and greater reliability • Digital technology also offers more efficient security, error detection and correction, compression, and ease of reproduction Information Technology in Theory