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

2. Information Technology in Theory
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. Information Technology in Theory
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. Information Technology in Theory
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. Information Technology in Theory
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. Information Technology in Theory
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. Information Technology in Theory
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. Information Technology in Theory
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. Information Technology in Theory
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. Information Technology in Theory
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. Information Technology in Theory
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. Information Technology in Theory
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. Information Technology in Theory
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. Information Technology in Theory
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