Secondary Storage

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Secondary StorageInput / Output
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Physical Parts

• Storage device
• Does the writing
• Storage Media
• Where the data is stored
• Internal
• floppy, hard drive, CD-ROM, DVD
• External
• slower but portable

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Drive Properties

• Drives are assigned letter designations
• letters ( Windows) Names ( Mac)
• Read / Write Heads
• Non Volatile
• Removable
• CD, floppy, DVD
• Fixed
• Hard disk

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Access to data

• Random
• implies addressing
• access only the required data
• Sequential
• computer tapes
• no addressing

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Representing Data

• Files / documents
• Directories / folders / sub folders
• Logical representation
• the way the user sees the files and directories
• Physical Representation
• the way the computer stores the information
• computer uses FAT to keep track of files
• files can be scattered across the storage media

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Magnetic Disk Systems

• Common storage media
• fast, reliable, cheap
• read / write heads
• magnetize particles
• Types
• Floppy removable media
• hard drives fixed media

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Floppy Disks

• 8 .. 5 1/4 .. 3 1/2
• 180K .. 1.44 meg
• formatted
• tracks .. rings
• sectors pie shaped sections
• cluster
• smallest addressable area
• spans several sectors
• FAT (file allocation table)
• database
• keeps track of addresses of data

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Hard Disks

• usually fixed media
• 4 - 8 metal platters
• 3 1/2 diameter
• 5400 -15000 rpm
• factory sealed
• multiple read / write heads
• external connects through bus system

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Hard Drive Addressing

• Rarely formatted
• F-disk, defrag
• tracks, sectors, and cylinders
• Cylinders
• several 1000 per hard drive
• same track and sector on all disks
• access more data without moving r/w head
• of tracks on a disk of cylinders
• Access mechanisms
• read / write arm between each set of platters
• clearance .5 one millionth of an inch
• a hair is 2500 millionth of an inch
• head crash

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Disk Access Time

• Three parts to reading / writing data
• seek time
• moving r/w head to correct cylinder
• rotation delay
• time used by the shaft to move disks into place
• data movement time
• time to read data and move it to RAM
• time to move data from RAM and write it

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Disk Cache

• Dedicated part of RAM
• fetches data stored near the requested data
• next data request, cache checked first
• data in disk cache removed using a formula
• uses circuits on disk controller card
• saves disk wear
• speeds program execution

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RAID

• redundant array of independent disks
• several drives used to store data
• performance
• fault tolerance
• records duplicate copies of data
• striping and mirroring
• Striping
• file spread over several disks
• better performance .. No fault tolerance
• Mirroring
• data written to two or more disks at the same
  time
• provides a backup if one disk fails

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Optical Disks

• Use laser beams
• r/w at higher densities than magnetic drives
• low capacity (700 meg) and slow
• removable
• CD and DVD
• used for software delivery
• optical libraries .. Radio stations

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CDs

• CD- ROM
• compact disk read only memory
• factory source, pits burned into surface ( high
  intensity laser)
• low intensity laser on computer reads data
• based on light reflection
• not re-writable
• Newer Format
• CD-R
• CD-RW

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DVDs

• High capacity storage 4.7 - 17 gig
• stores 120 minutes of video and sound
• will supplant CDs
• rewritable DVDs
• DVD-RAM
• DVDRW
• No standard set yet
• Expensive

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Other forms of Storage

• Magnetic Tape
• inexpensive
• reusable
• used for system backup
• high capacity
• Sequential Access only
• Smart Cards
• infancy stage
• credit card with circuitry
• holds about 1K of rewritable space
• mostly ROM
• cash card, access card, medical history,
  insurance information
• national identity card?? privacy

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• Flash memory Devices
• Memory Sticks / Memory Cards
• up to 64 meg
• usually needs a card or device to attach to
  computer
• good for photos, music
• Memory Drives
• 256 Meg
• expensive
• USB
• portable
• solid state

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Input and Output
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Overview

• Input devices
• convert human language to 0 - 1
• Output Devices
• convert 0 - 1 to human language
• Most devices are either input or output
• the modem is both input and output

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Input Devices

• Keyboards
• QWERTY
• 103 keys, function keys, numeric pad, special
  access
• wired or wireless
• keyboard port and USB
• folding keyboards
• access to laptops
• ergonomic keyboards

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Pointing Devices

• Mouse
• scroll wheel, ergonomic, wireless, optical /
  ball,
• click / double click, drag and drop
• serial, USB, PS2
• Electronic Pens
• alternative to mouse
• pointed at screen
• light senses location on monitor
• Used with
• Graphic tablets (designing and drawing)
• Digital portfolio
• Signature capture Devices ( UPS)
• Pen based Computers (replace clip boards)
• require handwriting recognition

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Other Input Devices

• Touch Screens
• kiosks, restaurants, specific purpose computers
• Joysticks
• games, simulations,
• trackball
• upside down mouse
• ergonomic
• pointing Stick
• found on some laptop computers
• touch pad
• laptops, alternative to the mouse

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Scanners

• Transfer data from source documents to the
  computer
• two methods
• scan as an image
• OCR
• Types of scanners
• Flatbed OCR, images, text, similar to
  photocopier
• Sheetfed like a fax, multiple sheets, cost
  effective
• Handheld short pieces of data, phone numbers
• 3-D scanners .. Graphics .. Manipulate 3-D images
• Resolution
• 300 -1200 dpi (72 - 150 dpi for web 300 dpi for
  print)
• file size related to image size and resolution
• grayscale - millions of colours

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Optical Readers

• Specialized scanners
• Use light to read information
• Optical marks bubble sheets
• Optical Characters
• specialized font design
• credit cards and monthly bills ( turn around
  documents)
• Optical Codes
• bar codes UPC
• hand held or stationary scanners
• MIRC
• Magnetic Ink Character Recognition
• banking industry
• allows for automated processing of cheques
• check amount added at time of processing

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Multimedia Input Devices

• Digital Cameras
• digital storage medium
• uses a disk or card
• adjusters, reporters,
• upload directly / via Internet
• Video Cameras
• edit home videos
• Audio Input devices
• voice input
• voice recognition ..
• accent, inflection, tone, mood
• background noise
• memory intensive

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Display Devices

• Monitors
• CRT radiation issue
• LCD
• HDTV
• Viewers
• CRT
• 15-21 viewing area smaller
• Resolution
• pixels .26 dot pitch
• 640 x 480 . 1280 x 1024

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Graphics Standards

• SGA current standard
• 16.7 million colours,
• video / graphics card .. Onboard RAM .. 64 meg
• colour monitors RGB ( red green blue)

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Flat Panel Displays

• Small footprint
• lightweight
• energy efficient
• Less Radiation
• LCD liquid crystal display
• liquid crystals sandwiched between two sheets of
  material
• colour filters manipulate light, create correct
  image
• Active-matrix vs passive-matrix
• active .. Sharper image, better viewing from an
  angle
• Gas Plasma
• layers of gas instead of liquid crystals
• expensive

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Printers

• Hand held to room size
• Resolution
• measured in dpi
• todays printers use rounded dots for printing
• Impact
• pins struck a ribbon, marked the paper
• older technolgy
• still used for multiple part forms ie receipts
• Non-impact
• laser and Inkjet
• no contact with paper
• quiet, fewer parts
• faster, reliable

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Laser Printers

• Personal
• 400 and up
• 4 - 12 ppm
• 600 dpi
• Professional
• 12 -40 ppm
• higher resolution
• usually networked
• multiple paper trays
• Colour Laser
• prices coming down

• Work like Photocopiers
• drum with dots
• charged by a laser beam
• toner attracted to charged areas
• toner transferred to paper
• paper heated, toner bonded

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Ink Jet Printers

• Personal use only
• slower
• colour
• tiny nozzles spray ink onto paper
• poorer quality
• expensive cartridges
• inexpensive printers

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Special Purpose Printers

• Photo Printers
• special paper
• insert memory stick
• near photo quality
• Bar Code printers
• shipping labels, price tags, parking tickets
• Wide Format
• plotters
• art blue prints
• print to a wide range of materials

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