Computer Architecture Reflective Journal Report

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Systems Architecture,
Seventh Edition

Chapter 7

Input/Output Technology

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Systems Architecture, Seventh Edition

Chapter Objectives

• In this chapter, you will learn to:
• Describe basic concepts of text and image representation and display, including digital representation of grayscale and color, bitmaps, and image description languages
• Describe the characteristics and implementation technology of video display devices
• Understand printer characteristics and technology
• Describe the main manual input technologies
• Describe types of optical input devices
• Identify the characteristics of audio I/O devices and explain how they operate

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Systems Architecture, Seventh Edition

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FIGURE 7.1 Topics covered in this chapter

Courtesy of Course Technology/Cengage Learning

Systems Architecture, Seventh Edition

Basic Print and Display Concepts

• Share many features
• Character representation methods
• Measurement systems
• Methods of generating color

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Systems Architecture, Seventh Edition

Matrix-Oriented Image Composition

• Display surfaces vary wide in size and composition
• Divided into rows and columns similar to a large matrix
• Each cell (pixel) represents one simple component of an image
• Resolution
• Number of pixels displayed per linear measurement unit
• Stated in dots per inch (dpi)

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Systems Architecture, Seventh Edition

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FIGURE 7.2 Text displayed in two resolutions: 50 dpi (top) and 200 dpi (bottom)

Courtesy of Course Technology/Cengage Learning

Systems Architecture, Seventh Edition

Fonts

• Collection of characters of similar style and appearance
• Usually measured in points (one seventy-second of an inch), which refers to height of characters

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Systems Architecture, Seventh Edition

FIGURE 7.3 The letters p and A represented in an 8x16 pixel matrix

Courtesy of Course Technology/Cengage Learning

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Systems Architecture, Seventh Edition

FIGURE 7.4 Sample characters printed in a variety of fonts

Courtesy of Course Technology/Cengage Learning

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Systems Architecture, Seventh Edition

FIGURE 7.5 A font (Times Roman) printed in different point sizes

Courtesy of Course Technology/Cengage Learning

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Systems Architecture, Seventh Edition

Color

• RGB (additive colors)
• Generates color by mixing red, green, and blue
• CMY (subtractive colors)
• Generates color using cyan (absence of red), magenta (absence of green), and yellow (absence of blue)
• CMYK color
• Four-dye scheme using a separate black dye (K)

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Systems Architecture, Seventh Edition

Numeric Pixel Content

• Bitmap
• Stored set of numeric pixel descriptions
• Monochrome display
• Displays one of two colors
• Requires only one bit per pixel
• Grayscale display
• Displays black, white, and shades of gray
• Chromatic depth or chromatic resolution

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Systems Architecture, Seventh Edition

Numeric Pixel Content (continued)

• Palette
• A table of colors
• Number of bits used to represent each pixel determines table size
• Dithering
• Generates color approximations by placing small dots of different colors in an interlocking pattern
• Half-toning (grayscale dithering)

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Systems Architecture, Seventh Edition

Image Storage and Transmission Requirements

• Depends on number of bits that represent each pixel and on image height and width in pixels
• Can be reduced with bitmap compression
• Graphics Interchange Format (GIF)
• Joint Photographic Experts Group (JPEG)
• Moving Pictures Experts Group (MPEG)
• All compression methods are lossy, resulting in some loss of image quality

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Systems Architecture, Seventh Edition

Image Description Languages (IDL)

• Address drawbacks of bitmaps (large size and device dependence) by storing images compactly
• Can represent image components in several ways
• Embedded fonts
• Vectors, curves, and shapes
• Embedded bitmaps

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Systems Architecture, Seventh Edition

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FIGURE 7.6 Elements of a vector (top) and two complex shapes built from vectors (bottom)

Courtesy of Course Technology/Cengage Learning

Systems Architecture, Seventh Edition

Adobe PostScript and Portable Document Format

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Systems Architecture, Seventh Edition

Video Display

• Character-oriented video display terminals (VDTs)
• Connected through dedicated low-speed communication links
• Only display text and primitive graphics

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Systems Architecture, Seventh Edition

Video Controllers

• Enables communication between computer system and monitor
• Accepts commands and data transmitted via a bus from the CPU
• Generates analog or digital video signals, which are transmitted to the monitor
• Terms:
• Refresh cycle and refresh rate; video RAM; dual porting; graphics accelerators

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Systems Architecture, Seventh Edition

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A video controller contains RAM, a microprocessor, and embedded software.

FIGURE 7.8 Video controller with monitor and bus connections

Courtesy of Course Technology/Cengage Learning

Systems Architecture, Seventh Edition

Video Monitors

• Separate from keyboards
• Common types
• Cathode ray tubes (CRTs) - obsolete
• Flat panel displays
• Liquid crystal displays (LCDs)
• Plasma displays
• LED displays

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Systems Architecture, Seventh Edition

LCD

• Contains matrix of liquid crystals sandwiched between two polarizing filter panels
• Active and passive matrix displays
• Manufactured with thin film transistor (TFT) technology

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Systems Architecture, Seventh Edition

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FIGURE 7.9 Light entering the rear filter can’t pass through the front filter if the liquid crystal is electrically charged (top); removing the charge returns the liquid crystal to its twisted state, allowing light to pass (bottom)

Courtesy of Course Technology/Cengage Learning

Systems Architecture, Seventh Edition

Plasma Displays

• Combine elements of CRT and LCD technology
• Flat panel, active matrix devices
• Actively generate colored light near surface of the display
• Good brightness and viewing
• Require more power than LCDs

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Systems Architecture, Seventh Edition

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FIGURE 7.10 A plasma display pixel

Courtesy of Course Technology/Cengage Learning

Systems Architecture, Seventh Edition

LED Displays

• Based on light-emitting diodes (LEDs)
• Modern LED displays use organic compounds to achieve improved color accuracy (OLEDs)
• In performance terms LED displays combine the best features of plasma and LCD displays
• Thin
• Low power consumption
• Wide viewing angle
• Can be manufactured as flexible sheets

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Systems Architecture, Seventh Edition

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FIGURE 7.11 Layers of a single OLED pixel

Courtesy of Course Technology/Cengage Learning

Cathode (-)

Anode (+)

Where the light is produced

More explanation about OLED, go here: https://www.explainthatstuff.com/how-oleds-and-leps-work.html

Systems Architecture, Seventh Edition

Printers

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Systems Architecture, Seventh Edition

Inkjet Printers

• Most common printing technology
• Prints with liquid ink placed directly onto paper
• Uses mechanical movement or heat to force ink out of nozzle
• Paper is drawn past moving print head
• Resolution is up to 1200 dpi

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Systems Architecture, Seventh Edition

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FIGURE 7.12 Ink drop formation and ejection in a thermal inkjet chamber

Courtesy of Hewlett-Packard Company; reproduced with permission

Systems Architecture, Seventh Edition

Printer Communication

• Impact printers
• Can print each character as it’s received
• Commonly uses small buffers
• Inkjet and laser printers
• Use pixels as fundamental output unit
• Have relatively large buffers
• IDLs (Image Description Languages) are commonly used to improve printer performance

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Systems Architecture, Seventh Edition

Laser Printers

• Operates with an electrical charge and the attraction of ink to this charge
• Color laser output uses three separate print generators
• Laser
• Drum
• Laser modulators

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Systems Architecture, Seventh Edition

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FIGURE 7.13 Components of a laser print engine

Courtesy of Course Technology/Cengage Learning

Systems Architecture, Seventh Edition

Plotters

• Printers that generate line drawings on wide sheets or rolls of paper
• Use inkjet technology
• Can produce any large output, including posters and banners
• Usually called large format printers

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Systems Architecture, Seventh Edition

Keyboards

• Translate keystrokes directly into electrical signals
• Generate bit stream outputs (scan code) with a keyboard controller
• Can connect to computer in various ways
  (e.g., PS/2, USB, wireless)

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Systems Architecture, Seventh Edition

Pointing Devices

• Include:
• Mouse
• Trackball
• Joystick
• Input pads (e.g., digitizer tablet)
• Infrared detector
• Photosensor
• Pressure-sensitive pad
• Magnetic fields

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Systems Architecture, Seventh Edition

Touch Screens

• Additional layers added to a flat panel display to detect touch
• Touch sensors (capacitors) are laid out in a grid and connected with traces
• Most common form is based on capacitance – the ability of a substance (e.g., a finger) to hold electrical charge
• Touching the screen interrupts the electrical field generated by embedded capacitors in a detectable way

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Systems Architecture, Seventh Edition

Optical Input Devices

• Detect light reflected off a printed surface or object into a photosensor
• Categories
• Mark and pattern sensors
• Image capture devices

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Systems Architecture, Seventh Edition

Mark Sensors and Bar-Code Scanners

• Mark sensor
• Scans for light or dark marks at specific locations on a page (e.g., standardized multiple-choice test)
• Bar code scanner
• Detects specific patterns of vertical bars of varying thickness and spacing
• Typically used to track large numbers of inventory items

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Systems Architecture, Seventh Edition

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FIGURE 7.15 Two-dimensional bar code formats

Courtesy of Course Technology/Cengage Learning

Systems Architecture, Seventh Edition

Optical Scanners

• Generate bitmap representations of printed images
• Bright white light shines on the page; reflected light is detected by an array of photosensors
• Optical character recognition (OCR) devices
• Combine optical-scanning technology with a special-purpose processor or software to interpret bitmap content

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Systems Architecture, Seventh Edition

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FIGURE 7.16 Sample form with OCR input fields

Courtesy of Course Technology/Cengage Learning

Systems Architecture, Seventh Edition

Digital Cameras

• Digital still cameras, video cameras, and Webcams use a 2D photosensor array placed behind lenses to capture reflected and focused ambient light
• Digital still camera
• Captures one image at a time
• Can configure to store images in a compressed format, such as JPEG

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Systems Architecture, Seventh Edition

Portable Data Capture Devices

• Used for warehouse inventory control and package routing, tracking and delivery
• Simpler devices function only as I/O devices
• More complex devices are portable computers with embedded I/O devices

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Systems Architecture, Seventh Edition

Audio I/O Devices

• Sound: an analog signal that must be converted to digital form for computer processing or storage
• Various mathematical transformations convert complex sounds to a single numeric representation
• Sampling and playback rely on analog-to-digital converters (ADC) and digital-to-analog converters (DAC)

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Systems Architecture, Seventh Edition

Audio I/O Devices (continued)

• Used in computer systems for:
• General-purpose sound output (e.g., warnings)
• General-purpose sound input (e.g., digital recording for voice email messages)
• Voice command input
• Speech recognition
• Speech generation
• Monophonic and polyphonic

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Systems Architecture, Seventh Edition

Speech Recognition

• Conceptually simple, but complicated by speaker variability, phoneme transitions and combinations, and real-time processing
• Most current systems are speaker dependent
• Digital signal processor (DSP)
• Specialized to process continuous streams of audio or graphical data
• Commonly embedded in audio and video hardware

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Systems Architecture, Seventh Edition

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FIGURE 7.17 The process of speech recognition

Courtesy of Course Technology/Cengage Learning

Systems Architecture, Seventh Edition

Speech Generation

• Audio response unit
• Generates spoken messages based on textual input (e.g., automated call routing)
• Speech synthesis
• Stores individual phonemes within the system
• General-purpose audio hardware (sound card, multimedia controller)

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Systems Architecture, Seventh Edition

General-Purpose Audio Hardware

• Typically packaged as an expansion card that connects to the system bus of a workstation
• Sound cards include an ADC, DAC, low-power amplifier, and connectors (jacks) for microphone, speaker, or headphone
• Musical Instrument Digital Interface (MIDI)
• Compact storage format

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Systems Architecture, Seventh Edition

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FIGURE 7.18 Components and connections of a typical sound card

Courtesy of Course Technology/Cengage Learning

Systems Architecture, Seventh Edition

Summary

• Concepts, technology, and hardware used in communication between people and computers
• Print and display concepts
• Video display devices
• Printers
• Manual input devices
• Optical input devices
• Audio I/O devices

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