Input Processing Output Storage Second part

1
InputProcessingOutputStorage (Second part)

• By Gustavo Alatta

2
Output Screen Features

• The device which displays computer output to us
  has various names
  
• Screen from "computer screen" or "display
  screen"
  
• Monitor  from its use as a way to "monitor" the
  progress of a program
  
• VDT video display terminal  from early network
  terminals
  
• CRT cathode ray tube   from the physical
  mechanism used for the screen. 
  
• VDU visual display unit  to cover all the
  mechanisms from desktop CRTs to LCD flat screens
  on laptops to LED screen on palmtops
  

3
Making Colored Pictures

• CRT screen
• A standard monitor screen is a CRT (cathode ray
  tube). The screen is coated on the inside surface
  with dots of chemicals called phosphors. When a
  beam of electrons hits a dot, the dot will
  glow. 
• On a color monitor these phosphor dots are in
  groups of three Red, Green, and Blue. This RGB
  system can create all the other colors by
  combining what dots are aglow.
• There are 3  signals that control the 3 electron
  beams in the monitor, one for each RGB color.
  Each beam only touches the dots that the signal
  tells it to light. All the glowing dots together
  make the picture that you see. The human eye
  blends the dots to "see" all the different
  colors.
• A shadow mask blocks the path of the beams in a
  way that lets each beam only light its assigned
  color dots. (Very cool trick!) 
  

4
Making Colored Pictures

• LCD screen
• LCD (Liquid Crystal Display) screens use an
  entirely different technique. The screen is still
  made of dots but is quite flat. LCD displays are
  made of two layers of a polarizing material with
  a liquid crystal solution in between. An
  electrical signal makes the crystals line up in a
  way that keeps light from going through entirely
  or just partly. A black screen has all the
  crystals lined up so that no light gets
  through. 
• A color LCD screen uses groups of 3 color cells
  instead of 3 phosphor dots. The signal for a
  picture cleverly lets just the right spots show
  their colors. Your eye does the rest.
• Scan Pattern
• There are two patterns used by different
  monitors to cover the whole screen. Both scan
  across the screen, in a row 1 pixel high, from
  left to right, drop down and scan back left. 
• The non-interlaced pattern scans each row of
  pixels in turn, from top to bottom. This type is
  more prone to flicker if the scan has not started
  over by the time the phosphor dots have quit
  glowing from the last scan. This can make your
  eyes hurt or even make you nauseous.
• The interlaced pattern scans every other row of
  pixels. So the odd rows are done, then the even
  rows, in the same left to right to left way. But
  since the rows of pixels are very close together,
  the human eye doesn't notice as easily if a row
  has gone dim before it is rescanned. Much
  friendlier to your eyes and stomach.
• Light vs. Ink
• Colors created by glowing dots are not quite the
  same as those created by ink on the printer.
  Screens use the RGB system described above. Inks
  use the CMYK system using the colors Cyan (a kind
  of blue), Magenta (a kind of red), Yellow, and
  blacK. This is why what you see on your screen is
  not quite the same color when you print.

5
Screen Features

• Size Desktop screens are usually 14 - 19 in. by
  diagonal measurement. (This is how TV screens are
  measured, too.) Larger sizes are available, at a
  significantly higher cost. Prices are dropping,
  however. 
• Resolution
• Determines how clear and detailed the image is.
  Pictures on a screen are made up of tiny dots.
  1 dot on screen 1 pixel (from "picture
  element") The more pixels per inch, the clearer
  and more detailed the picture.   One measure of
  this is the dot pitch, the distance between the
  dots that make up the picture on the screen.
  However, different manufacturers measure
  differently. Most measure from dot center to the
  center of the nearest same color dot. Some
  measure from the center of a dot to an imaginary
  vertical line through the center of the nearest
  dot of the same color, giving a smaller number
  for the same dots as the previous method. Some
  monitors use skinny rectangles instead of dots
  and so must use a different method altogether.
  So, dot pitch has become less useful as a measure
  of monitor quality. A dot pitch of .28 is very
  common and .26 should be good for nearly all
  purposes, however it is measured. 
• Refresh RateHow often the picture is redrawn on
  the monitor. If the rate is low, the picture will
  appear to flicker. Flicker is not only annoying
  but also causes eye strain and nausea. So, a high
  refresh rate is desirable. 60 times per second is
  tolerable at low resolutions for most people. 75
  times per second or more is better and is
  necessary for high resolutions. 

6
Screen Features

• Type
• CGA, EGA, VGA, super VGADetermines what
  resolutions are available and how many colors can
  be displayed.
  
• New systems now come with super VGA with a
  picture size of 800 x 600 pixels (as a minimum)
  and 16 million colors 
  

7
Screen Features

• ColorThe number of colors displayed can vary from
  16 to 256 to 64 thousand to 16.7 million. The
  more colors, the smoother graphics appear,
  especially photos. The number of colors available
  actually depends more on the video card used and
  on how much memory is devoted to the display. It
  takes 8 bits to describe 1 pixel when using 256
  colors. It takes 24 bits per pixel when using 16
  million colors. So a LOT of memory is needed to
  get those millions of colors. Video cards now
  come with extra memory chips on them to help
  handle the load. 
• Reverse video  example
• Cursor/ Pointer The symbol showing where you are
  working on the screen, like    and 
  
• In the olden days of just DOS, there were few
  choices for the cursor. The invention of the
  blinking cursor was a tremendous event. Under
  Windows there are a huge number of basic to
  fantasy cursors to choose from. 
• ScrollingMoving the lines displayed on the screen
  up or down one line at a time
  

8
Type of Screens

• Monochromeone color text on single color
  background, i.e. white letters on blue, or green
  characters on black
  
• Colorvarious colors can be displayed. (This one
  is easy!)
  

CRTThe most common type of monitor, which uses a
cathode ray tube. Liquid Crystal Display (LCD)Us
ed in laptops esp. Large flat monitors are
becoming affordable, especially if you do not
have desk space for a large CRT monitor.
Plasma ScreensUsed for very large screens and
some laptops. Flat, good color, but quite
expensive.
9
Output Other Devices 

• Special tasks require special equipment. There
  are a number of special-use output devices. More
  are announced every day. From recording
  earthquake tremors to displaying CAT scans, from
  recording analysis in a sound studio to
  displaying metal fatigue in aircraft structures,
  we have more and more special tasks that use
  computers and thus require print or screen
  display.
• Data projectors Projects the image onto a wall
  screen
  
• Microfilm (COM)   Computer Output MicrofilmThe
  computer directly generates the microfilm
  images.
  

10
Output Other Devices

• Large Format Printers
• Used especially for building plans and
  engineering drawing and really large pictures.
  
• Plotters use a pen to draw continuous lines and
  are favored for engineering drawings, which
  require both large sheets of paper and precise
  lines.
• Sound  
• Computers can output voice messages, music, data
  as sound. Of course you have to have speakers and
  a sound card.
  

11
QUESTIONS?