Lecture 05

INTRODUCTION TO COMPUTER

LECTURE 05

OUT PUT DEVICES There are currently just three common types of output devices, monitor, printer and sound system.

THE MONITOR

In three output devices monitors. The most important because they are the output devices with which users inter act most often. Two basic types of monitors are used with PCs. The first is the typical monitor that you see on a desktop computer. It looks a lot like a television screen and works the same way. This type uses a large vacuum tube, called a cathode ray tube (CRT).

How a CRT Monitor Displays an Image Near the back of monochrome or grayscale monitor housing is an electron gun. The gun shoots a beam of electrons through a magnetic coil, which aims the beam at the front of the monitor. The back of the monitor’s screen is coated with phosphors, chemicals that glow when they are struck by the electron beam. The screen’s phosphor coating is organized into a grid of dots. The smallest number of phosphor dots that the gun can focus on is called a pixel, a contraction of picture element. Modern monochrome and grayscale monitors can focus on pixels small as single phosphor dot. A color monitor works just like a monochrome one, except that there are three electron beams instead of just one. The three guns represent the primary additive colors (red, green, and blue), although the beams they emit are colorless, each pixel on the screen is made up of three tiny red, green, and blue phosphors arranged in a triangle. When the beams of each of these guns are combined and focused on a point on the screen, the phosphors at that point light up to form a tiny spot of whiter light. Different colors can be displayed by combining various intensities of the three beams. Resolution: The resolution of a computer monitor is classified by the number of pixels on the screen, expressed as a matrix. For example, a resolution of 640 x 480 means here are 640 pixels horizontally across the screen and 480 pixels vertically don the screen. Dot Pitch : The last critical specification of a color monitor is the dot pitch, the distance between the phosphor dots that make up a single pixel. Plotters J print.

SOUND SYSTEMS Just as microphones are now important input devices, speakers and their associated technology are key output systems. Today, when you buy a multimedia PC, you are getting a machine that includes a CD-ROM drive, a high-quality video controller (with plenty of VRAM), speakers, and a sound card. The speakers attached to these systems are similar to ones you connect to a stereo. The only difference is that they are usually smaller, and they contain their own small amplifiers. Otherwise, they do the same thing any speaker does; they transfer a constantly changing electric current to a magnet, which pushes the speakers cone back and forth. The moving speaker cone creates pressure vibrations in the air---in other words, sound.

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INTRODUCTION TO COMPUTER

LECTURE 05

SERIAL AND PARALLEL PORTS

Internally, a PC’s components communicate through the data bus, which consists of parallel wires. Similarly, a parallel interface is a connection where there are eight or more wires through which data bits can flow simultaneously. Most computer buses transfer 32 bits simultaneously. However, the standard parallel interface for external devices like printer usually transfers eight bits (one byte) at a time over eight separate wires. With a serial interface, data bits are transmitted one at a time through a single wire (however, the interface includes additional wires of r the bits that control the flow of data). Inside the computer, a chip called a UART converts parallel data from the bus into serial data that flows through a derail cable. Serial ports are most often used to connect a mouse or a modem.

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