Application

  • CAD (Computer Aided Design)
  • CAM (Computer Aided Manufacturing)
  • DTP (Desktop Publishing)

Plotters

Graphics output device to create drawings on paper

1. Pen Plotter

  • Electromechanical device 
  • Moved in two dimension across paper/film media
  • Ink pens & Multiple color pens are used

Types of Pen Plotters

  • Drum Plotter – Drum rotates & Pen carriage moves horizontally
  • Microgrip Plotter – Medium gripped at edges–moved  to & fro
  • Flatbed Plotter – Pen carriage moved along X & Y axis in short digital steps using stepper motor

2. Photo Plotter

  • Uses fiber optics tech
  • Produce image on dry silver paper
  • Size: A4, A3, etc
  • Expensive 
  • Excellent Quality
  • Can prepare quick & beautiful engineering drawings
  • Can be interfaced to computer via serial & parallel interface

Light pen

  • I/p device in CAD application that can indicate current active position to 1 program
  • Photo sensor detects presence of light – connected via cable to computer
  • When tip of light pen touches a spot on CRT,light pen is activated
  • Light is sensed & signal is sent to micro computer
  • Computer notes the position of spot where light pen is touched

Joystick

  • High accuracy not needed & used in simple application
  • Used in playing games for creation of general symbol shapes
  • A Lever protrudes through top of unit & can be tilted at different angles
  • Joy stick can control cursor on CRT screen – visual indication to user
  • Rate of speed of cursor is directly propositional to distance of joystick lever from vertical position

 

Digitiser or graphic tablet

  • Has flat surface like drawing pad & pointing device
  • X-Y line co ordinate system converts rough sketch to fine drawing by transferring point & line location to computer 
  • Pointing devices: Stylus/Pen, Push button cursor/Puck, Power module or console menu
  • Grid platter of horizontal & vertical line below flat surface of digitiser detects electrical pulses at X-Y coordinate
  • Popular i/p device in CAD
  • Available in many sizes

Magnetic tape drives (Start / stop drives)

  • Oldest device for storage by older main frames & mini computer
  • Tape spool of 2400 feet – easy & convenient to transport files to store data & even OS
  • It has 9 tracks across length – 8 bits off data & 1 parity bit – CRCC
  • For each track, tape drives had 9 set of heads, each having Erase, Write & Read heads
  • Head assembly – fixed & tape media moved
  • Positioning mechanism: Vacuum Column or Tension arm System
  • Recording Tech NRZI (Non return to zero Inverted)
  • Important back up device during data loss
  • Tape housed in cartridge. (Quarter inch Cartridge)

Tape Drive Capacity No of tracks Interface Transfer speed Remarks
Quater inch catridge(QIC) 40 MB-13 GB 9 to 144 QIC/SCSI-2/Parallel port 12 MB/min - 18 MB/min Ideal for servers
Full size QIC Mini Catridge 40 MB- 13 GB 20 to 144 Floppy/IDE/SCSI/QIC 2 MB/Min - 9 MB/Min Smaller size; Ideal for PCs
Travan tape 40 MB - 4GB 36 to 72 Floppy/EIDE/SCSI 62.5KB/sec - 567 KB/sec Higher density
Helican scan tape: 4mm digital audio tape(DAT) & 8 mm 2 GB - 4 GB Full surface EIDE/SCSI   Full tape surface used

QIC drive

  • Faster tape than casette tape
  • Holds 300 or 600 feet of tape
  • Mini cartridge holds 62.48-m (205’) quarter-inch tape
  • Uses MFM or Run Length Limited (RLL) (s/w cares it)
  • High recording density – Travan Tape Cartridge drive

Helical – Scan tape drive

  • R/W heads mounted on drum

  • Rotation – 2000 RPM

  • Tape wraps about 90o around drum’s circumference

  • Slight angle between tape’s path & drum

  • Helical span path formed by moving drum on moving tape

  • Complete surface of tape is used

Backup

  • Slower tape drives. So longer time for back up
  • Server uses RAID (Redundant Array of Inexpensive Drives) with multiple disk drives
  • Cost is higher – worth for critical server data