Video Chapter 17

1
VideoChapter 17
2
Objectives

• Explain how video displays work
• CRT and LCD monitors
• Understand the concept of resolution
• Explain refresh rates and how they affect
  monitors
• Select the proper video Card
• Graphics Processor
• Video Memory

3
Introduction

• The term video encompasses a complex interaction
  among numerous parts of PC, all designed to put a
  picture on the screen.
• Video consists of two devicesthe video card
  (display adapter)
• and the monitor
• (Video displays)

Video card
Monitor
4
Video Card

• The video card consists of two distinct
  components
• One takes commands from the computer and updates
  its own onboard RAM
• The other scans the RAM and sends data to the
  monitor
• Therefore Video card handles all communications
  between CPU and monitor.
• OS needs to know how to handle communication
  between CPU and display adapter, which requires
  BIOS.

5
Monitors
6
CRT Monitors

• CRT is Cathode Ray Tube (CRT), which is type of a
  vacuum tube.
• One end of this tube is a slender cylinder that
  consists of three electron guns.
• The wide end of the CRT is the display screen.

7
CRT Monitors

• The inside of the display screen has Phosphor
  coating.
• When power is applied to one or
• more of the electron guns,
• a stream of electrons shoots
• towards the display end of CRT.
• This stream is subjected to a magnetic field
  generated by a ring of electromagnets called a
  yoke
• that controls the electron beams point of
  impact.

8
CRT Monitors

• The phosphor coating releases energy as visible
  light when struck by the electrons.
• Phosphors continue to glow momentarily after
  being struck by electron beamsquality of
  phosphors is called persistence
• Too much persistence and the image is smeary
• Too little persistence and the image appears to
  flicker.

9
CRT Refresh Rates
10
CRT Refresh Rates
Video data is displayed on the monitor starting
at the upper-left corner of the monitor ending to
the lower- right corner. Each line are called
raster line. How many line in screen?

• Horizontal refresh rate (HRR)
• The speed at which the electron beam moves across
  the screen and to be ready for the next line.

• Vertical refresh rate (VRR)
• The amount of time taken by the monitor to draw
  the entire screen and get the electron beam back
  to the start.

11
CRT Refresh Rates

• The Monitor does not determine the HRR or VRR.
• Video cards push the monitor at a given VRR, and
  then the monitor determines the HRR
• If the VRR is set too low, youll see flicker

• If it is set too high, youll
• have a distorted screen image
• and may damage the monitor.

• Multisync (multiple-frequency monitor) monitors
  support multiple VRRs.

12
Phosphors

• Phosphors are dots inside the CRT monitor that
  glow red, green, or blue when an electron gun
  sweeps over them.
• CRT has three electron guns one for read
  Phosphor, one for green Phosphors and one for
  blue Phosphors.

• The higher the intensity of the electron stream
  the higher the color produced by Phosphors.

13
Phosphors

• How we can prevent the red electron beam from
  bleeding over and lighting neighboring blue and
  green dots?

• Shadow mask is a screen that enables only the
  proper electron gun to light the proper phosphor.

• The area of phosphors lit at one time by a group
  of guns is called a picture element, or pixel

14
Phosphors
Triad

• A pixel consists of at least 3 phosphor dots

15
Resolution

• Resolution is always shown as the number of
  Horizontal Pixel times the Vertical Pixel.
• A resolution of 640 X 480 means
• Number of horizontal pixel is 640 and vertical
  pixel is 480.
• If you multiply the values together you get
  307200? What does it means?
• Resolution affecting the pixel
• size.

16
Common Resolutions

• 640x480 307,200 pixels per screen
• 800x600
• 1024x768
• 1280x960
• 1280x1024
• 1600x1200
• Most of these resolutions matches a 43 ratio
  (called aspect ratio)
• Many monitors (wide-screen monitors) have 169 or
  1610 ratio. Ex. 1366x768 and 1920x1200

17
Resolution

• Maximum possible resolution
• Determined by how small can one pixel be.
• Theoretically, a triad, but various limitations
  in screens, controlling electronics, and electron
  gun technology make smallest pixel much bigger
  than one triad.

18
Dot Pitch

• Dot pitchdiagonal distance between phosphorous
  dots of the same color.
• Range from 0.39 mm to as low as 0.18 mm
• The lower the dot pitch, the more dots across
  the screen, which produces a sharper, more
  defined image

19
LCD monitors

• Use Liquid crystal displays
• Have many advantage over CRT
• Thinner and lighter.
• Much less power.
• Flicker free.
• No harmful radiation.
• Called flat panels or flat panel displays .

20
Video Cards
21
Video Cards

• Video cards are composed of two major pieces
• Video RAM to store video image.
• Video processor- GPU which takes information from
  video RAM and shoots it out to the monitor.
• Video card need fan to cool their onboard
  processor.
• Monitor plugs into the
• video card.

22
Color depth

• Each pixel in screen has color
• This color are stored in video RAM using tiny
  number of bits depend on the number of color you
  want.
• i.e. to get 256 colors, each pixel would have to
  be represented with 8 bits.
• Color depths determined by bits per pixel
• 2 colors 1 bit (mono)
• 4 colors 2 bits
• 16 colors 4 bits
• 256 colors 8 bits

23
Color depth

• Windows XP offers 32-bit color.

24
Video RAM Requirements

• Depends on Resolution Colour Depth

1024 x 768 786432 pixels per screen
Example
32 bit colour 4 bytes per pixel.
4 x 786432 3145728 bytes.
3 megabytes per screen.
25
Video Modes

• Your video card and monitor are capable of
  showing Windows in a fixed number of different
  resolutions and color depths.
• The choices depend on the resolutions and color
  depths the video card can push to the monitor and
  the amount of bandwidth your monitor can support.
• Any single combination of resolution and color
  depth you set for your system is called a mode.

26
Video Modes

• VGA

Video Graphics Array

• Supported 640 x 480 pixels and 16 Color.
• Every video card made in the last 15 years can
  Output as VGA, but VGA-only cards are now
  obsolete. Check Your PC?
• Minimum display requirement by many software
  package.

27
Video Modes

• Beyond VGA
• SVGA, XGA, and more

Typical Device Aspect ratio Resolution Mode
PDA and small video player 43 320x240 QVGA
Small monitors 43 800x600 SVGA
Monitor and portable projector 43 1024x768 XGA
Small widescreen laptop 1610 1280x800 WXGA
LCD monitors 54 1280x1024 SXGA
Widescreen laptop 1610 1440x900 WSXGA
28
Motherboard connection

• Data moving from video card to display has to go
  through the video cards memory chips and
  expansion bus and this can happen only so
  quickly.
• PCI, AGP, PCIe
• The standard PCI slot transfers 32 bits at speed
  33 Mhz, yielding a max. bandwidth of 132 MBps.
  This may be enough until you use higher
  resolution, higher color depth and higher refresh
  rate.

29
Motherboard connection

• A typical display at 800x600 with 70 HZ refresh
  rate and 8 bit color depth. How much data per
  second has to be sent to the display?
• 800 x 600 x 1 byte x 70 33.6 MBps.
• Using 24-bit color, the amount of data sent jumps
  to 100.8 MBps.
• Although 132 MBps of PCI looks sufficient, but
  most systems have more than one PCI device each
  requiring part of this throughput.

30
AGP

• Intel answered the desire for video bandwidth
  even higher than PCI with Accelerated Graphics
  Port (AGP)
• AGP a single special port similar to PCI slot
  dedicated to video.
• It is derived from the 66-MHz, 32- bit PCI 2.1
  spec.
• It uses a function called strobing that increases
  the signals 2, 4, and 8 times for each clock
  cycle (called AGP x1, x2, x4, x8)

31
AGP cont.

• AGP has several technological advantages over
  PCI
• It resides alone on its own personal data bus
  connected directly to Northbridge.
• It takes advantages of pipelining commands
  similar to CPU pipelining.
• It has a feature called sidebanding a second
  data bus that enables video card to send more
  commands to northbridge while receiving others at
  same time.

32
Accelerated Graphics Port
33
PCIe

• PCIe developed to replace PCI and AGP.
• PCI and AGP are using a parallel interface.
• It is a natural evolution for video as it is
  incredibly fast, using serial communication
  method.
• All PCIe video cards use PCIe x16 connector

34
Graphics Processor

• Graphics Processor Unit (GPU)
• The most important decision in buying a video
  card is the graphics processor and amount of RAM
  onboard.
• The graphics processor handles the heavy lifting
  of taking commands from the CPU and translating
  them into coordinates and color information that
  the monitor understands and displays.

35
Graphics Processor

• Most video processors are made by
• NVIDIA
• ATI
• ATI Radeon X1950 XTX 512 MB
• ATI Manufacturer
• Radeon X1950 XTX Processor Model No.
• 512 MB Amount of RAM

36
Graphics Processor

• NVIDIA and ATI release multiple models of
  graphics processors each year
• Most features only seen in 3-D games
• Textures
• Transparency
• Shadows
• Reflection

37
Video Memory

• Video RAM constantly updates to reflect every
  change that takes place on the screen
• Different video modes require different amount of
  memory.
• DRAM slower but cheaper
• VRAM is specialized Video RAM
• more expensive but faster. It can read and write
  data at same time

38
Video Memory

• WRAM (Window RAM) is slightly faster than VRAM
  but not as widely accepted
• SGRAM (synchronous graphics RAM) is sync-ed to
  the system clock
• Now DDR SDRAM is used.