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ObjectivesObjectives Explain how video displays workExplain how video displays work

CRT and LCD monitorsUnderstand the concept of resolutionUnderstand the concept of resolutionExplain refresh rates and how they affect Explain refresh rates and how they affect

monitors monitors Select the proper video CardSelect the proper video Card

Graphics ProcessorVideo Memory

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IntroductionThe term video encompasses a complex

interaction among numerous parts of PC, all designed to put a picture on the screen.

Video consists of two devices—the video card (display adapter)

and the monitor (Video displays)

3Monitor Video card

Video CardThe 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 Video card : handles all communications between CPU and monitor.

OS needs to know how to handle communication between CPU and display adapter, which requires BIOSBIOS.

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MonitorsMonitors

CRT Monitors CRT is Cathode Ray Tube (CRT), which is

type of a vacuum tube.

One end of this tube is a slenderslender cylinder that consists of three electron guns.

The widewide end of the CRT is the display screen.

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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

yokeyoke that controls the electron beams point of impact. 7

CRT Monitors The phosphor coating releases energy as as

visible light visible light when struck by the electrons.

Phosphors continue to glow momentarily after being struck by electron beams—quality of phosphors is called persistence

Too much persistence and the image is smearysmeary Too little persistence and the image appears to

flickerflicker.

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CRT Refresh RatesVideo 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 lineraster line. How How

many line in screenmany line in screen?? Horizontal refresh rate Horizontal refresh rate

(HRR)(HRR)

The speed at which the

electron beam moves

across the screen and to

be ready for the next

line.

Vertical refresh rate Vertical refresh rate

(VRR)(VRR)

The amount of time

taken by the monitor to

draw the entire screen

and get the electron

beam back to the start.

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, you’ll see flicker

If it is set too high, you’ll

have a distorted screen image

and may damage the monitor. MultisyncMultisync (multiple-frequency monitor)

monitors support multiple VRRs.

Phosphors

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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.

Phosphors

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

Phosphors

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Triad

A pixel consists of at least at least 3 phosphor dots

Resolution Resolution is always shown as the number of

Horizontal Pixel Horizontal Pixel timestimes the Vertical PixelVertical 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?What does it means?

Resolution affecting the pixel size.

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Common Resolutions 640x480 = 307,200 pixels per screen 800x600 1024x768 1280x960 1280x1024 1600x1200

Most of these resolutions matches a 4:3 ratio (called aspect ratio)

Many monitors (wide-screen monitors) have 16:9 or 16:10 ratio. Ex. 1366x768 and 1920x1200

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Resolution Maximum possible resolutionMaximum 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.

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Dot Pitch Dot pitchDot pitch—diagonal distance between

phosphorous dots of the same color.

Range from 0.390.39 mm to as low as 0.180.18 mm

The lower the dot pitch, the more dots across the screen, which produces a

sharper, more defined image

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LCD monitorsUse Liquid crystal

displaysHave many advantage

over CRT:Thinner and lighter.Much less power.Flicker free.No harmful

radiation.Called flat panels flat panels or

flat panel displaysflat panel displays .

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Video CardsVideo cards Video cards are composed of two major pieces : Video RAM Video RAM to store video image. Video processorVideo processor- GPUGPU 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.

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Color depthEach 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 pixel2 colors = 1 bit (mono) 2 colors = 1 bit (mono) 4 colors = 2 bits 4 colors = 2 bits 16 colors = 4 bits 16 colors = 4 bits 256 colors = 8 bits 256 colors = 8 bits

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Color depthWindows XP offers 32-bit color.

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Video RAM RequirementsDepends on Resolution + Colour Depth

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Example: 1024 x 768 = 786432 pixels per screen

32 bitbit colour = 4 bytesbytes per pixel.

4 x 786432 = 3145728 bytes.

= 3 megabytes per screen.

Video ModesYour 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 modemode.

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Video ModesVGAVGA

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Video Graphics Array

Supported 640 x 480 640 x 480 pixels and 16 16 ColorColor.

Every video card made in the last 15 years can Output as VGA, but VGA-only cards are now obsolete. Check Your PC?Check Your PC?

Minimum display requirement by many software package.

Video ModesBeyond VGABeyond VGA

SVGA, XGA, and more

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Mode Resolution Aspect ratio

Typical Device

QVGA 320x2404:3PDA and small video player

SVGA 800x600 4:3Small monitors

XGA 1024x768 4:3Monitor and portable projector

WXGA 1280x800 16:10Small widescreen laptop

SXGA 1280x1024

5:4LCD monitors

WSXGA

1440x900 16:10Widescreen laptop

Motherboard connectionData moving from video card to display has to

go through the video card’s 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.

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A typical display at 800x600 with 70 HZ A typical display at 800x600 with 70 HZ refresh rate and 8 bit color depth. How much refresh rate and 8 bit color depth. How much data per second has to be sent to the display?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 MBps100.8 MBps.

Although 132 MBps of PCI looks sufficient, but most systems have more than one PCI device each requiring part of this throughput.

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Motherboard connection

AGP Intel answered the desire for video

bandwidth even higher than PCI with Accelerated Graphics Port (AGP)

AGP: a singlesingle 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 strobingstrobing that increases the signals 2, 4, and 8 times for each clock cycle (called AGP x1, x2, x4, x8)

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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 sidebandingsidebanding: a second data bus that enables video card to send more commands to northbridge while receiving others at same time. 31

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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

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• 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.

Graphics Processor

• Most video processors are made by:– NVIDIA– ATI

• ATI Radeon X1950 XTX Radeon X1950 XTX 512 512 MB– ATI Manufacturer– Radeon X1950 XTX Processor &

Model No.– 512 MB Amount of RAM

Graphics Processor

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

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

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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.

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