Computer Peripherals
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,
Interface SCSI,
Computer Peripherals
USB, serial
to systems bus
IDE, PCMCIA Englander, The Architecture of Computer Hardware and Systems Software An Information Technology Approach, 3rd ed., 2003
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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
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
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10 to 50 milliseconds 95 milliseconds 100 to 600 milliseconds .5 and up seconds Englander, The Architecture of Computer Hardware and Systems Software An Information Technology Approach, 3rd ed., 2003
600 to 6,000 KB/sec 100 to 200 KB/sec 500 to 4,000 KB/sec 2,000 KB/sec
(cartridge)
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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
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Magnetic Disks Consist of one or more flat, circular platters made of glass, metal or plastic and coated with a magnetic substance.
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Magnetic Disks (cont.)
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
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Magnetic Disks (cont.) Head crash 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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Cutaway of a floppy disk
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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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Magnetic Disks
Data Block Format
Interblock
Disk Interleaving
gap
Header
Data
Formatting
disk
Disk
Interleaving Disk Arrays
RAID
– mirrored, striped
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RAID (striping)
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RAID (mirroring)
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Magnetic Tape Offline
storage Archival purposes Disaster recovery
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QIC Can hold 120 MB to 25 GB of uncompressed data.
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DAT Data on DAT cartridges are very tightly packed, using a read/write head that rotates at a high speed to pack the tape much more tightly with data. Very tiny but have capacities of 2GB and up.
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Optical Storage A direct access disk written and read by light. CD, CD-ROM, DVD-ROM and DVDVideo are read-only optical disks that are recorded at the time of manufacture and cannot be erased.
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Types of Optical Storage CD-ROM DVD-ROM WORM Magneto optical disks
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CD-ROM Read-only removable medium with large data storage capacity. Data storage is similar to magnetic disk. Laser beam is reflected off the pitted surface of the disk as a motor rotates the disk.
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Layout: CD-ROM vs. Standard Disk CD-ROM
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Hard Disk
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DVD-ROM Similar to the CD-ROM technology. Uses laser with a shorter light wavelength to allow tighter packing of the disk. Total capacity: 17GB
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WORM Disks Write-once-read-many times Similar to the CD-ROM technology Medium can be altered by using a mediumpowered laser to blister the surface Data stored in concentric tracks, sectored like a magnetic disk
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Magneto-Optical Disks Combine optical and magnetic disk technology. Share advantages of optical disk: capacity, reasonable cost & removability together with the read/write capability of magnetic disks.
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Magneto-Optical Disks (cont.) May be stored near magnets. Limitation: have a much longer seek time & a slower transfer rate than magnetic disks.
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Magneto-Optical Disks (cont.)
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Displays Images made up of thousands of individual
pixels or picture element
Pixel: The smallest addressable unit on a
display screen or bitmapped image. Screens are rated by their number of horizontal and vertical pixels 1024x768 means 1024 pixels are displayed in each row, and there are 768 rows (lines). Computer Peripherals
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Simplest Pixel Representation
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Display Screen Screen size: measured diagonally Resolution: minimum identifiable pixel size
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Displays Screen (cont.)
How to select a PC display screen: Acceleration and multimedia
Monitor size and resolution
LCD or CRT
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Acceleration & Multimedia Placing drawing functions into the circuits of the display adapter speeds up rendering on screen. Adding graphics accelerator & video accelerator cards
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Acceleration & Multimedia
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Monitor size & resolution
Standard resolutions: 640x480
800x600
1024x768
1280x1024
1600x1200
The higher the resolution, the more material is viewable on screen.
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Displays Screen
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Color and Displays Pixel color is determined by intensity of 3 colors – Red Green Blue or RGB RGB: The computer's native color space. It is also the color system for capturing images and displaying them. Human eyes are sensitive to red, green and blue, and all colors are perceived as a combination of the R, G and B.
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CRT
Cathode Ray Tube A vacuum tube used as a display screen in a computer monitor or TV.
The viewing end of the tube is coated with red, green and blue phosphors dots, which emit light when struck by electrons.
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CRT
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Raster scan Displaying or capturing a video image line by line from left to right.
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LCD – Liquid Crystal Display A display technology that uses rod-shaped molecules (liquid crystals) that flow like liquid and bend light.
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LCD (cont.)
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Plasma Display Gas discharge display Uses tiny cells lined with phosphor that are full of inert ionized gas
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Plasma Display (cont.)
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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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Printers
General Categories
Serial Printers (Character Printers)
Line Printers
Page Printers
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Serial Printer Prints one character at a time moving across the paper. Eg. serial dot matrix printer, with speeds ranging from 200 to 400 cps (90 to 180 lines per minute)
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Dot Matrix Uses hammers and a ribbon to form images out of dots. Forms characters and graphics by impacting a ribbon and transferring dots of ink onto the paper.
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Dot Matrix (cont.)
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Line Printer Print a line at a time from approximately 400 to 2,000 lpm Eg. Line Matrix printer
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Line Matrix
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Line Matrix (cont.)
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Page Printer Prints a page at a time from four to more than 800 ppm. Eg. Laser Printer
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Laser Printer Uses a laser and the electrophotographic method to print a full page at a time. The laser "paints" a charged drum with light, to which toner is applied and then transferred onto paper.
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Laser Printer
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Other Printers Ink jet Dye sublimation Thermal Wax transfer
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Ink Jet Propels droplets of ink directly onto the medium. Makes use of an ink jet cartridge
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Ink Jet Printer
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Dye sublimation printer Produces continuous-tone images that look like photographic film. Also called a "thermal dye printer”. The print cartridge contains a cellophane ribbon with panels of dye the same size as the page to be printed.
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Dye sublimation printer (cont.)
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Dye Sublimation Printer
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Thermal wax transfer printer Uses the same printing mechanism as a dye sublimation printer. Instead of using a dye, it melts dots of wax-based ink that adhere to almost any kind of stock, from ordinary paper to complex synthetics and film.
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Thermal wax transfer printer
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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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Scanner
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Telephone modems
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