The architecture of computer hardware and systems software an information technology approach ch10

transfer rate  Access time: average time it takes a computer to locate data and read it  Data transfer rate: amount of data that moves per second... Secondary Storage Devices Hard d

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

 Devices that are separate from the

basic computer

 Classified as input, output, and storage

 Connect via

 Ports

 parallel, USB, serial

 Interface to systems bus

 SCSI, IDE, PCMCIA

Storage Devices

primary memory for CPU access

transfer rate

 Access time: average time it takes a

computer to locate data and read it

 Data transfer rate: amount of data that moves per second

Hierarchy of Storage

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

Secondary Storage Devices

 Hard drives, floppy drives

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

A Hard Disk Layout

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

Disk Access Times

 average time to move from one track to another

 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

 RAID – mirrored, striped

 Majority logic  fault-tolerant computers

Disk Interleaving

Disk Block Formats

Single Data Block

Header for Windows disk

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

 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)

Optical Storage

 Reflected light off a mirrored or pitted surface

 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

 4.7G per layer

 Max 2 layers per side, 2 sides = 17G

Optical Storage

 Laser strikes land: light reflected into detector

 Laser strikes a pit: light scattered

Layout: CD-ROM vs Standard Disk

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

Types of Optical Storage

 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

Display Screen

diagonally

identifiable pixel size

 Aspect ratio: x pixels to

y pixels

 4:3 on most PCs

 16:9 on high definition

displays

Color and Displays

 Pixel color is determined by intensity of

3 colors – Red Green Blue or RGB

 4 bits per color

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

 A character is the smallest unit on a screen

 Very little memory required

 Fast for remote transmissions

Interlaced vs Noninterlaced

Diagram of Raster Screen

Generation Process

Display Example

LCD – Liquid Crystal Display

 Fluorescent light panel

 3 color cells per pixel

 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

LCD Operation

 One transistor per row or column

 Each cell is lit in succession

 Display is dimmer since pixels are lit less frequently

 Dots vs pixels

 300-2400 dpi vs 70-100 pixels per inch

 Dots are on or off, pixels have intensities

 Typewriter / Daisy wheels – obsolete

 Dot matrix – usually 24 pins, impact printing

 Inkjet – squirts heated droplets of ink

 Laserjet

 Thermal wax transfer

 Dye Sublimation

Creating a Gray Scale

Laser Printer Operation

the electrically charged places

the paper

drum

Laser Printer Operation

Laser Printer Operation

Other Computer Peripherals

 Flatbed, sheet-fed, hand-held

 Light is reflected off the sheet of paper

tablets