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 devices—the 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 slendercylinder 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 beams—quality 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 • Videodata 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, you’ll see flicker • If it is set too high, you’ll • 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 higherthe color produced by Phosphors.

13. Phosphors • How we can prevent the red electron beam from “bleeding over” and lighting neighboring blue and green dots? • Shadowmask 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, orpixel

14. Phosphors Triad • A pixel consists of at least 3 phosphor dots

15. Resolution • Resolution is always shown as the number of Horizontal Pixel timestheVertical 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 4:3 ratio (called aspect ratio) • Many monitors (wide-screen monitors) have 16:9 or 16:10 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 pitch—diagonal 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. • Noharmful 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. Colordepth • 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. Colordepth • Windows XP offers 32-bit color.

24. Video RAM Requirements Depends on Resolution + Colour Depth 1024 x 768 = 786432 pixels per screen Example: 32 bitcolour = 4 bytes per pixel. 4 x 786432 = 3145728bytes. = 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

28. Motherboard connection • Data 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.

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 singlespecial 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 • ATIRadeon X1950 XTX 512 MB • ATI Manufacturer • Radeon X1950 XTX Processor & Model No. • 512 MB Amount of RAM

36. GraphicsProcessor • 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.