Chapter 9

Report
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
Chapter 10 Computer Peripherals
10-2
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
Chapter 10 Computer Peripherals
10-4
Hierarchy of Storage
Device
Typical Access Times
Throughput Rate
CPU Registers
Cache Memory (SRAM)
15 to 30 nanoseconds
Conventional Memory (DRAM)
50 to 100 nanoseconds
Expanded Storage (RAM)
75 to 500 nanoseconds
Hard Disk Drive
Floppy Disk
CD-ROM
Tape
Chapter 10 Computer Peripherals
10 to 50 milliseconds
95 milliseconds
100 to 600 milliseconds
.5 and up seconds
600 to 6,000 KB/sec
100 to 200 KB/sec
500 to 4,000 KB/sec
2,000 KB/sec
(cartridge)
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. Seek time
 average time to move from one track to another
 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)
 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 Interleaving
 Disk Arrays
 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
Chapter 10 Computer Peripherals
10-15
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
Chapter 10 Computer Peripherals
Hard Disk
10-17
CD-ROMs
General Speed
Seek Time
(milliseconds)
Single-Speed
600
150K per second
2X
320
300K per second
3X
250
450K per second
4X
135-180
600K per second
6X
135-180
900K per second
8X
135-180
1.2 MBps
10X
135-180
1.6 MBps
12X
100-150
1.8 MBps
16X
100-150
2.4 MBps (maximum)
24X
100-150
3.6 Mbps (maximum)
32X
100-150
4.8 Mbps (maximum)
Chapter 10 Computer Peripherals
Data Transfer Rate
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 – picture element
 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!
Chapter 10 Computer Peripherals
10-22
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
 1st 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
Chapter 10 Computer Peripherals
10-27
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
Chapter 10 Computer Peripherals
10-29
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. Dots of laser light are beamed onto a drum
2. Drum becomes electrically charged
3. Drum passes through toner which then sticks to
the electrically charged places
4. Electrically charged paper is fed toward the
drum
5. Toner is transferred from the drum to the paper
6. The fusing system heats and melts the toner
onto the paper
7. 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
Chapter 10 Computer Peripherals
10-35
Copyright 2003 John Wiley & Sons
All rights reserved. Reproduction or translation of this
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information contained herein.”
Chapter 10 Computer Peripherals
10-36

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