Chapter 10

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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

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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

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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

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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

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Hierarchy of Storage

Device 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 10 to 50 milliseconds 600 to 6,000 KB/sec Floppy Disk 95 milliseconds 100 to 200 KB/sec CD-ROM 100 to 600 milliseconds 500 to 4,000 KB/sec Tape .5 and up seconds 2,000 KB/sec (cartridge)

Typical Access Times

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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

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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

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A Hard Disk Layout

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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

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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

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Magnetic Disks

 Data Block Format

 Interblock gap

 Header

 Data

 Formatting disk

 Disk Interleaving

 Disk Arrays

 RAID – mirrored, striped

 Majority logic  fault-tolerant computers

Disk Interleaving

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Disk Block Formats

Single Data Block

Header for Windows disk

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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

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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)

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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

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Optical Storage

 Laser strikes land: light reflected into detector

 Laser strikes a pit: light scattered

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Layout: CD-ROM vs. Standard Disk

CD-ROM Hard Disk

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CD-ROMs

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)

General Speed Data Transfer Rate

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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

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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

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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

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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!

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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

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Interlaced vs Noninterlaced

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Diagram of Raster Screen

Generation Process

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Display Example

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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

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LCD Operation

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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

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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

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Creating a Gray Scale

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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

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Laser Printer Operation

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Laser Printer Operation

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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

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