Video

• Monitor CRT: Cathode Ray Tube

• The screen is coated with tiny dots of phosphor material, called pixels, that glow when electrically charged.

• Electron beam moves back and forth, working top to bottom and left to right one row at a time, lighting up phosphor dots on inside of tube

Refresh rate• Speed with which a monitor redraws images

on the screen

– Time it takes for electron beam to paint the screen from top to bottom

• expressed in Hertz, e.g., 70 Hz= 70 times per second

• the higher the refresh rate, the less flickering and the easier on your eyes

Interlacing

• Interlaced monitors draw the screen in two passes- even lines on the first pass and odd on the second pass

• lower quality- more flicker than noninterlaced

Shadow mask monitor

• Shadow mask

• metal screen with thousands of tiny holes

Resolution

• Resolution= number of pixels monitor can display.

• Number of horizontal pixels x number of vertical pixels, e.g., 640 x 480 means 640 pixels in each horizontal row, 480 vertically

• Higher resolution means a greater number of pixels display and smoother image

Dot pitch

• Dot pitch is a measure of image clarity

• Represents the distance between each pixel.

• The smaller the dot pitch, the clearer the displayed image.

• Expressed in millimeters, e.g., .28 mm, .25 mm, etc.

Video Cards• Video card converts digital output into an

analog video signal sent through a cable to the monitor.

• Composed of video RAM and video processor in modern cards (older cards did not have a video co-processor and used CPU for these calculations- MUCH slower!)

Types of Video memory

– VRAM- Video RAM- requires less refresh than regular DRAM

– WRAM- Windows RAM- faster than VRAM

– SGRAM- Synchronous Graphics RAM- very fast!, because it’s synchronized to system clock (like SDRAM)

How much video memory?• A video card must have enough RAM to

draw image on screen

• To calculate how much video RAM is required for a given resolution and number of colors (see Gilster p. 202):

– 1. Multiply the desired resolution x number of color bits

– 2. Divide product by 8

Video modes:

• MDA: Monochrome Display Adapter- old!

• CGA: Color Graphics Adapter

• 320x200 (4 colors) or 640x200 (2 colors)

• EGA: Enhanced Graphics Adapter (EGA)

• 16 colors, resolution of 640x350

Video modes continued

• VGA: Video Graphics Array

• 640x480, 16 colors

• (256 colors at lower resolution)

• Super VGA:

• up to 1280 x 1024 and up to 16 million colors

Monitor connectors

• 15-pin VGA connector is standard monitor and video card connector

• 9-pin used in older monitors (CGA, EGA, early VGA)

• BNC connectors used in some high-end monitors

Monitor safety• The monitor uses more power than the rest

of the computer put together and produces very strong electromagnetic emissions (20,000 volts, even when power is off!)

• Best to avoid working on monitors- never use ESD grounding strap with monitor

• Energy Star standard: EPA program to reduce monitor energy consumption by 99 percent in suspend mode