Chapter 10

Computer Peripherals

The Architecture of Computer Hardware and Systems Software: An Information Technology Approach 3rd Edition, Irv Englander John Wiley and Sons



2003 Wilson Wong, Bentley College Linda Senne, Bentley College

Peripherals

   Devices that are separate from the basic computer  Not the CPU, memory, power supply Classified as input, output, and storage Connect via  Ports  parallel, USB, serial  Interface to systems bus  SCSI, IDE, PCMCIA 10-2 Chapter 10 Computer Peripherals

Storage Devices

   Primary memory Expanded storage Secondary storage  Data and programs must be copied to primary memory for CPU access  Permanence of data    Direct access storage devices (DASDs) Online storage Offline storage – loaded when needed Chapter 10 Computer Peripherals 10-3

Speed

 Measured by access time and data transfer rate  Access time: average time it takes a computer to locate data and read it  millisecond = one-thousandth of a second  Data transfer rate: amount of data that moves per second 10-4 Chapter 10 Computer Peripherals

Hierarchy of Storage

Device

CPU Registers Cache Memory (SRAM) Conventional Memory (DRAM) Expanded Storage (RAM) Hard Disk Drive Floppy Disk CD-ROM Tape

Typical Access Times Throughput Rate

15 to 30 nanoseconds 50 to 100 nanoseconds 75 to 500 nanoseconds 10 to 50 milliseconds 600 to 6,000 KB/sec 95 milliseconds 100 to 200 KB/sec 100 to 600 milliseconds 500 to 4,000 KB/sec .5 and up seconds 2,000 KB/sec (cartridge) Chapter 10 Computer Peripherals 10-5

Secondary Storage Devices

       Hard drives, floppy drives CD-ROM and DVD-ROM drives CD-R, CD-RW, DVD-RAM, DVD-RW Tape drives Network drives Direct access vs. Sequential access Rotation vs. Linear Chapter 10 Computer Peripherals 10-6

Magnetic Disks

     Track – circle Cylinder – same track on all platters Block – small arc of a track Sector – pie-shaped part of a platter Head – reads data off the disk     Head crash Parked heads Number of bits on each track is the same! Denser towards the center.

CAV – constant angular velocity    Spins the same speed for every track Hard drives – 3600 rpm – 7200 rpm Floppy drives – 360 rpm Chapter 10 Computer Peripherals 10-7

A Hard Disk Layout

Chapter 10 Computer Peripherals 10-8

Locating a Block of Data

 Average seek time: time required to move from one track to another  Latency: time required for disk to rotate to beginning of correct sector  Transfer time: time required to transfer a block of data to the disk controller buffer Chapter 10 Computer Peripherals 10-9

Disk Access Times

  Avg. Latency time   average time to rotate to the beginning of the sector Avg. Latency time = ½ * 1/rotational speed  Transfer time  1/(# of sectors * rotational speed)  Avg. Seek time  average time to move from one track to another Total Time to access a disk block  Avg. seek time + avg. latency time + avg. transfer time Chapter 10 Computer Peripherals 10-10

Magnetic Disks

   Data Block Format     Interblock gap Header Data Formatting disk Disk Interleaving Disk Arrays  

Disk Interleaving

RAID – mirrored, striped Majority logic  fault-tolerant computers Chapter 10 Computer Peripherals 10-11

Disk Block Formats

Single Data Block Header for Windows disk

Chapter 10 Computer Peripherals 10-12

Alternate Disk Technologies

   Removable hard drives  Disk pack – disk platters are stored in a plastic case that is removable  Another version includes the disk head and arm assembly in the case Fixed-head disk drives   One head per track Eliminates the seek time Bernoulli Disk Drives  Hybrid approach that incorporates both floppy and hard disk technology  Zip drives Chapter 10 Computer Peripherals 10-13

Magnetic Tape

    Offline storage Archival purposes Disaster recovery Tape Cartridges      20 – 144 tracks (side by side) Read serially (tape backs up) QIC – quarter inch cartridge (larger size) DAT – digital audio tape (small size) Size typically includes (2:1 compression) Chapter 10 Computer Peripherals 10-14

Optical Storage

   Reflected light off a mirrored or pitted surface CD-ROM  Spiral 3 miles long, containing 15 billion bits!

  CLV – all blocks are same physical length Block – 2352 bytes    2k of data (2048 bytes) 16 bytes for header (12 start, 4 id) 288 bytes for advanced error control DVD-ROM   4.7G per layer Max 2 layers per side, 2 sides = 17G 10-15 Chapter 10 Computer Peripherals

Optical Storage

  Laser strikes land: light reflected into detector Laser strikes a pit: light scattered Chapter 10 Computer Peripherals 10-16

Layout: CD-ROM vs. Standard Disk

CD-ROM Hard Disk

Chapter 10 Computer Peripherals 10-17

CD-ROMs

General Speed

Single-Speed 2X 3X 4X 6X 8X 10X 12X 16X 24X 32X Chapter 10 Computer Peripherals

Seek Time (milliseconds)

600

Data Transfer Rate

150K per second 320 250 300K per second 450K per second 135-180 135-180 600K per second 900K per second 135-180 135-180 100-150 100-150 100-150 100-150 1.2 MBps 1.6 MBps 1.8 MBps 2.4 MBps (maximum) 3.6 Mbps (maximum) 4.8 Mbps (maximum) 10-18

Types of Optical Storage

   WORM Disks   Write-once-read-many times Medium can be altered by using a medium-powered laser to blister the surface  Data stored in concentric tracks, sectored like a magnetic disk  CAV Medium-powered laser blister technology also used for   CD-R, DVD-R, DVD-ROM CD-RW, DVD-RW, DVD-RAM, DVD+RAM Magneto-Optical Disks Chapter 10 Computer Peripherals 10-19

Displays

    Pixel – pic ture el ement Size: diagonal length of screen Resolution (pixels on screen)   VGA: 480 x 640 SVGA: 600 x 800   768 x 1024 1280 x 1024 Picture size calculation  Resolution * bits required to represent number of colors in picture  Example: 16 color image, 100 pixels by 50 pixels 4 bits (16 colors) * 100 * 50 = 20,000 bits Chapter 10 Computer Peripherals 10-20

Display Screen

   Screen size: measured diagonally Resolution: minimum identifiable pixel size Aspect ratio: x pixels to y pixels   4:3 on most PCs 16:9 on high definition displays Chapter 10 Computer Peripherals 10-21

Color and Displays

 Pixel color is determined by intensity of 3 colors – Red Green Blue or RGB  4 bits per color  16 x 16 x 16 = 4096 colors  24 bit color (True Color)  16.7 million colors  Video memory requirements are significant!

10-22 Chapter 10 Computer Peripherals

CRT’s and Text Monitors

  CRTs (similar to TVs)    3 stripes of phosphors for each color 3 separate electron guns for each color Strength of beam  brightness of color  Raster scan   30x per second Interlaced vs. non-interlaced (progressive scan) Text monitors  24 lines x 80 chars    A character is the smallest unit on a screen Very little memory required Fast for remote transmissions Chapter 10 Computer Peripherals 10-23

Interlaced vs Noninterlaced

Chapter 10 Computer Peripherals 10-24

Diagram of Raster Screen Generation Process

Chapter 10 Computer Peripherals 10-25

Display Example

Chapter 10 Computer Peripherals 10-26

LCD – Liquid Crystal Display

   Fluorescent light panel 3 color cells per pixel Operation   1 st filter polarizes light in a specific direction Electric charge rotates molecules in liquid crystal cells proportional to the strength of colors  Color filters only let through red, green, and blue light  Final filter lets through the brightness of light proportional to the polarization twist 10-27 Chapter 10 Computer Peripherals

LCD Operation

Chapter 10 Computer Peripherals 10-28

LCDs (continued)

 Active matrix    One transistor per cell More expensive Brighter picture  Passive matrix  One transistor per row or column   Each cell is lit in succession Display is dimmer since pixels are lit less frequently 10-29 Chapter 10 Computer Peripherals

Printers

  Dots vs. pixels   300-2400 dpi vs. 70-100 pixels per inch Dots are on or off, pixels have intensities      Types  Typewriter / Daisy wheels – obsolete Dot matrix – usually 24 pins, impact printing Inkjet – squirts heated droplets of ink Laserjet Thermal wax transfer Dye Sublimation Chapter 10 Computer Peripherals 10-30

Creating a Gray Scale

Chapter 10 Computer Peripherals 10-31

Laser Printer Operation

1.

2.

3.

4.

5.

6.

7.

Dots of laser light are beamed onto a drum Drum becomes electrically charged Drum passes through toner which then sticks to the electrically charged places Electrically charged paper is fed toward the drum Toner is transferred from the drum to the paper The fusing system heats and melts the toner onto the paper A corona wire resets the electrical charge on the drum Chapter 10 Computer Peripherals 10-32

Laser Printer Operation

Chapter 10 Computer Peripherals 10-33

Laser Printer Operation

Chapter 10 Computer Peripherals 10-34

Other Computer Peripherals

 Scanners   Flatbed, sheet-fed, hand-held Light is reflected off the sheet of paper  User Input Devices  Keyboard, mouse, light pens, graphics tablets  Communication Devices   Telephone modems Network devices 10-35 Chapter 10 Computer Peripherals

Copyright 2003 John Wiley & Sons

All rights reserved. Reproduction or translation of this work beyond that permitted in Section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the permissions Department, John Wiley & Songs, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information contained herein.” 10-36 Chapter 10 Computer Peripherals