gmu it 212 - spring 20071 displays, i/o, portable computers, multimedia it 212 002 how computers...

GMU IT 212 - Spring 2007 1

Displays, I/O, Portable Computers, Multimedia

IT 212 002How Computers Work

April 26, 2007


Lecture Agenda Chapter 16: How a Computer Display Works Chapter 17: How Data Gets into Your PC Chapter 18: How Scanners Capture Images

and Words Chapter 19: How Portable Computers Work Chapter 21: How Multimedia Sound Works Chapter 22: How Multimedia Video Works


Chapter 16: How a Computer Display Works


Overview Various types of display technologies can be found

in the market today: CRT LCD Plasma

A monitor displays millions of colors on the screen by combining 3 fundamental colors: Red, Green and Blue (RGB)

A single pixel of an image displayed on the screen is typically comprised of 3 smaller dots, one for each color component Pixel = picture element


CRT: Cathode Ray Tube

Cathode Ray Tubes (CRT) monitors have been largely replaced by Liquid Crystal Displays (LCD) nowadays

A CRT monitor comprises a cathode ray tube with an electron gun that emits 3 electron beams

The electron beams in turn strike a screen coated with 3 types of phosphors Each electron beam is used to produce a single color component

Phosophors are materials that fluoresce when electrons are impinged on them

Each electron beam strikes a single dot on the screen making it glow The intensity of each electron beam is varied to control the amount of

fluorescence of each dot Different colored pixels are created by varying the intensity of each electron

beam


CRT The electron beam scans the phosphor screen in a raster scan format which

means that after the beams make one horizontal sweep across the screen, they go back and make a second horizontal sweep across the screen This is called raster scanning

The persistence of the phosphor glow enables the eye to see an uninterrupted image

The screen is repainted about 60 times per second (or higher) This is called the refresh rate

Some displays can paint only every other line on the screen at one pass and then go and paint the other lines during the second pass This is called interlacing and creates a higher resolution image with less expensive

components This however causes the screen to flicker

The beams are deflected using a component called a magnetic deflection yoke which uses EM fields to bend the path of the electron beams

The video graphics adapter card sends signals to the electron gun to produce the electron beams

The intensity of each beam is controlled by the signals issued by the adapter


CRT The adapter card receives the digital information

from the imaging software and converts the digital information into analog signals using a DAC converter

These signals are then fed to the CRT to control the intensity of each electron beam

There are various display standards for PCs including: VGA (Video graphics Array) SVGA (Super Video Graphics Array) XGA (Extended Graphics Array) UXGA (Ultra Extended Graphics Array)

They mainly differ in their resolutions


CRT


CRT The main problem associated with CRTs is their bulkiness owing

to the electron beams that must span across the screen and their high power consumption To scan the screen, the electron gun generating these beams

must be positioned at a certain distance away from the screenbulkiness

This drawback may be overcome by using a combination of phosphor dots and individual, smaller electron guns striking these phosphor dots Each phosphor dot may have its own electron beam striking it This technology is called Surface-Conduction Electron-Emitter

Display (SED) and is a new technology that provides a flat display but is much cheaper than plasma displays

It also requires fewer materials compared to LCDs


LCD: Liquid-Crystal Display LCD monitors use liquid crystal trapped

inside small cells instead of phosphor dots painted on the screen liquid crystals are liquid chemicals whose

molecules can be aligned precisely when subjected to electrical fields (PCWorld)

An illuminating bulb resides at the back of the cells and sends light onto the array of cells

A polarizing filter polarizes the light sent by the illuminating bulb—it aligns light vertically

The light passes through liquid crystal layer The molecules of the liquid crystal can

change alignment by applying electrical signals to each liquid crystal cell

3 cells make up a single color of the display After the liquid crystal layer is a color filter

A red color filter will allow only red light to pass through and will block other colors of light

Similarly, blue and green color filters only allow blue and green light to pass through

Finally there is a horizontal filter

www.pcworld.com


LCD Molecules in liquid crystals can become

twisted by varying degrees No electric field molecules naturally

“twist” the light to make it horizontal Electrical field molecules straighten and

light is not bent The twisting of the molecules affects the

polarization angle of the light passing through them Control this by strength of electrical field

The light that passes through the cells then strikes the filters Each filter only passes light of a specific

color The color light from the filter passes

through another polarizing filter and the 3 colors combined make up the unique color of each pixel Horizontal filter only lets horizontal direction

light throughwww.pcworld.com


LCD In summary: LCD Operation

Works by controlling polarization of light Liquid crystals can rotate polarization of light. By

varying the voltage on a single cell, one can: Rotate light controllably between 0 and 90 degrees Angle of polarization passing through polarization filter

controls the intensity of the light of the color which is seen


Plasma Displays A plasma display contains many tiny cells filled with

a mixture of xenon and neon gases Each cell acts as a tiny bulb that emits different colors

of light Each pixel on the screen is made up of 3 of these tiny

bulbs By applying varying levels of electricity to each cell,

the gas inside the cell may be turned into a plasma that emits light at different intensities

One side of each cell is coated with a type of phosphor Cells that are meant to produce green light are coated

with a phosphor material that gives off green light Similarly, cells that are meant to produce blue and red

light are coated with a phosphor material that gives off blue and red light respectively

By varying the amount of electricity applied to each cell, the plasma display creates different colors of light for each pixel

A combination of thousands/millions of these pixels creates an entire image

More power than LCD


Plasma Cross Section


Digital Light Processing A digital light processing (DLP) projector projects bright and sharp images

onto the screen It works by shining a light through a spinning wheel divided into red, green and

blue filters The light that goes through the colored filters strike millions of mirrors on the

surface of a DLP chip Each mirror corresponds to a single pixel on the screen and is attached to a hinge to

tilt the mirror When the mirror tilts, it reflects the light through a lens and onto the screen

As the red filter passes over the light source, it only passes red light The red light that has passed through the red filter reaches the mirrors Each mirror is held tilted for a specific duration controlled by the electricity applied to it The duration that the mirror is held tilted determines the level of red color within each

pixel This process is repeated as the filter spins to pass only green and only blue light

respectively The persistence of human vision causes the eye to see pixels with various

colors


Chapter 17: How Data Gets into Your PC


Overview The Keyboard is one of the primary device to input

information into the PC Mouse is also another popular device The basic way that a keyboard works has not

changed significantly since its introduction


Keyboard and Scan Codes Pressing a key on the keyboard causes a change in the amount of current

flowing through a circuit associated with a specific key The microprocessor on the keyboard constantly scans the circuits leading to the

keys It detects the increase/decrease in current from a key that has been pressed Each key has a different code that can be recognized by the processor Depending on the key pressed, the processor detects the change in current and

generates a number called a scan code There are two scan codes for each key, one when the key is depressed and

another when it is released The processor stores the number in the keyboard buffer for the BIOS to read

KEYBOARD MICROPROCESSOR(www.howstuffworks.com)

KEYBOARD MATRIX


Keyboard and Scan Codes The BIOS reads the scan code and sends a signal to the keyboard to

delete the scan code from the buffer The BIOS then writes to the RAM to maintain a record of which key was

pressed The BIOS also translates the scan code into an ASCII code The key is then displayed by the OS or application software


Keyboard and Scan Codes QWERTY layout

Layout chosen to slow down manual typist to keep keys from jamming


Alternate: Dvorak Simplified Keyboard (DSK) – 1930’s


Keyboard Connectors Use USB or PS/2

connector IBM Personal System/2

Pin Pin Description (Signal Name) 1 +KBD Data 2 Not used3 Ground 4 +5.0 volt dc 5 +KBD CLK 6 Not used


The Mechanical Mouse As the mouse moves, a protruding ball turns in the

direction of the movement As the ball rotates it turns two rollers mounted 90

degrees relative to each other One is for horizontal movements the other is for

vertical movements Each roller is attached to a wheel called an

encoder On the rims of the encoder are tiny metal contact

points Two pairs of contact bars also extend from the housing

of the mouse Each time a contact bar touches a contact point an

electrical signal is generated Or there is an infrared LED and sensor. The encoder

has holes on the rim to break the beam of light into the sensor.

How often the signal is generated is translated into how fast the mouse moves on the screen

Tapping either of the buttons on the mouse sends a signal to the PC which passes it on to the software

Based on the number of clicks and the exact position of the mouse during the click, the software performs the task you want to accomplish


The Optical Mouse As you move an optical mouse, and LED (Light

Emitting Diode) lights up the surface the mouse is on and bounces back to hit a CMOS sensor

A digital black and white camera at the bottom of the mouse takes hundreds of photos a second looking for differences in the images that indicate the speed and direction of the mouse

Signals from the camera are fed to the digital signal processor of the mouse

The information from the processor is fed to the computer which uses the data to reposition the mouse on the screen

Optical mice are usually more expensive than mechanical mice LEDs confused by polished or glass surfaces

Wireless mice are also very popular Wireless mice send signals using radio waves to a

receiver attached to one for the computer’s USB ports Some mice even use Bluetooth connections

www.howstuffworks.com


Touchpad Is comprised of layers of electrodes

row in horizontal row in vertical

Layers do not touch positive charge builds up on one row negative charge builds up on the other

Circuitry monitors capacitance between layers 100 times each second

Finger entering the area changes that points capacitance circuitry determines finger’s center and computer

horizontal/vertical intersection point


Pointing Stick Looks like an erase head (miniature joystick) Four force sensing resistors

forward,backward, left, right - directions

Finger pressure on the resistors changes resistance to allow more current flow

Microcontroller monitors amounts of current flowing through sensing resistors and uses that information to translate the finger pressure into on-screen cursor movements


Pointing Device Tips

Mechanical mice need care and feeding periodic maintenance will wear out use mouse pad whenever possible


Speech Recognition A person who is going to use speech recognition software must go

through a process called enrollment which consists of a person dictating text that is already known to the software for 10 minutes to an hour From this, the software creates vocal references which are ways in which the

speaker’s pronunciation of phonemes varies from models of speech based on a sample of hundreds to thousands of people

Phonemes are the smallest units of sound that combine into words such as “duh,” “aw”, “guh” in dog.

There are 48 phonemes in English After enrollment, the speaker dictates the text that needs to be

converted into text As the speaker speaks, ADC circuits sample the analog sound waves

and convert the audio signal into a binary stream Which is then compressed and adjusted by the speech engine to

correct the phonemes


48 Phonemes


Speech Recognition The acoustic recognizer compares the corrected phonemes to

known phonemes For each phoneme the recognizer finds the phoneme in a database

that most closely matches the phoneme To form words, the speech engine compares groups of successive

phonemes to a database of known words and selects the most appropriate word

For words that sound the same but are written differently such as “their” and “there”, they are turned over to a natural language component which compares the sounds with grammatical rules and selects the most appropriate one If the speech engine cannot make a selection, it may ask the

speaker to select the appropriate word Cell phones have simplified systems without training


Chapter 18: How Scanners Captures Images and Words


Scanners The basic element of any computer scanner is the CCD or charge

coupled device A CCD is an array of small cells called photodiodes A photodiode is a device that is capable of generating electricity when light

strikes it The amount of electricity that can be generated by the photodiode is

dependent on the intensity of the light striking it A flatbed scanner has a light source that illuminates the piece of paper

laying flat on the glass surface of the scanner A scanner works by relying on the reflection of this light from the different

regions of the paper Blank or white spaces reflect light more than dark regions do

A scan head attached to a motor moves over the paper and captures the light reflected from each individual area of the page

The light from the page is reflected through a system of mirrors


Scanners A lens focuses the beams of light

onto the photodiodes of the CCD that translate light levels into levels of electricity

The more light that is reflected, the greater the electricity generated by the photodiodes

If the scanner is a color scanner, the reflected light is directed through red, green and blue filters positioned in front of individual diodes

An ADC circuit converts each analog electricity reading into a digital value and a digital number is generated for each pixel

This digital vale is then sent to the software where it is stored in the appropriate image format


ScannersScanner Issues: Personal (inexpensive to own) High Quality Copyright violations (easy to do)

books, writing works, etc. Forgeries

documents currency IDs

Manipulation/alternations


Optical Character Recognition In order to implement character recognition, the document is scanned

by a scanner The scanner creates a bitmap image of the document with pixels that

are either black or white The Optical character Recognition (OCR) software reads the bitmap

and averages out the zones The whitespace between lines of text within a block defines each line’s

baseline, an essential detail for recognizing the characters in the text The software then tries to match images to text by trying to match each

character though a pixel by pixel comparison to character templates that it holds in memory

If any character is unrecognized then the OCR software further passes the character through a process called feature extraction

In feature extraction, the software calculates the character’s height and analyzes it further

If there is still no match then a special characters such as # is placed in place of it


Optical Character Recognition Many OCR programs also employ a spell

checker to correct any mistakes Most OCR programs also give the option of

saving the document in a variety of popular file formats recognized by word processors and spreadsheets


Optical Character Recognition Scanned page for OCR


Optical Character Recognition OCR’d text

The (ult of the Internet

W-. e write ”electricity” with a small ”e,” but the fact that the ”I” in ”Internet” is written in capital letters is symptomatic of the cult that surrounds it. The high-flown metaphors that are used to name this universe (from ”cyberworld” to ”virtual world”), as well as the routine expressions (the in- evitable ”information society”), clearly tell us that we are dealing with some- thing quite different from a simple tool. Veneration of the Internet leads to misuse of language: new techniques are called ”new technologies.” As a sociol- gist of communication, Philippe Breton calls into question the ”cult of the In- Telnet in a short book that is lively and stimulating: le Cults de l’Internet. Une menace pour le lien social? (The Cult of the Internet. A Threat to the Social


Chapter 19: How Portable Computers Work


Overview The size of portable computers is not necessarily

limited by our ability to manufacture smaller and smaller chips

It is due to the fact that a computer must be of a certain size for that we can interact with them on a human scale

The size of our fingertips dictates that a useable keyboard must be at least of a certain size

Our eyes also demand a display that cannot be very small in size


Overview Objectives

Minimize size, weight, power consumption for portability

Constraints: viewing area, keyboard, mouse, power capacity

Realities Typically 2x cost of comparable PC

lags desktop capabilities Upgrading is difficult, if not impossible

economically practical?


Notebook PCs There are several components in notebook

PCs that are different than desktop PCs and several components that are common to both

Some of the components include: AC adapter Batteries Built-in modem RAM Touchpad Infrared Port Display Keyboard PC card slot External Bus Floppy drive and CD-ROM drive


Notebook PCs AC adapter

Converts the AC voltage from wall outlet into DC voltage levels Batteries

Usually constitutes the bulkiest and heaviest part of the notebook Some notebooks provide a slot to include a secondary battery for

longer lifetime Built-in modem

Allows easy connection to the Internet Sometimes is a software modem

RAM Designed to fit into specialized slots Off the shelf desktop DIMMS and SIMMS cannot be used with

notebooks Touchpad

Takes the place of a mouse


Notebook PCs Infrared Port

Allows file transfers between a laptop and a desktop Display

LCD Keyboard

Has smaller keys than a regular keyboard Reduced keys Tighter pitch Shorter travel

PC card slot Allows other peripherals to be added easily Can serve the function of a hard drive, modem, network

connection or connection to external CD-ROM drive Many laptops have 2 PC card slots


Notebook PCs External Bus

Used to connect notebook to docking station where it can access ordinary desktop monitor, keyboard, mouse, etc

Floppy drive and CD-ROM drive Often combined into one component or they can take turns

using a drive bay


Notebook PC (Intel Processors) Celeron family

Intel Celeron M Pentium family

Intel Pentium M Core family

Intel Core Solo Mobile Intel Core Duo Mobile Intel Core 2 Duo Mobile

M or Mobile means lower power than desktop processor

Intel Centrino combines an Intel mobile processor with wireless LAN capabilities

MOREPOWERFUL


Notebook PCs Heat Dissipation Is a Problem

Battery heats up during use Fan cools electronic components Components switched off or clock speed lowered

to reduce power consumption Sound Card, Video Controller, Modem, all

Built Into Motherboard (not upgradeable) PCMCIA/PC Cards Allow Moderate Upgrade

Memory, modems, NIC, storage, High Tech I/O


Notebook PCs

Notebook Tips: Buy new current version versus upgrade of older

machine RAM upgrades may be practical/economical

Disable Infrared (IR) port (security) Portability invites theft

Secure data Encryption Physical (off-line storage if possible)


PC Cards PC cards were earlier called PCMCIA cards They are used to expand the capability of the laptop

and plug into a slot at the side of the laptop Most PC Cards contain non-volatile memory which

stores configuration information about itself [called Card Information Structure or CIS] Used by the device driver to provide information about the

card A device driver is software that is an extension to the

operating system to provide access to the hardware Sometimes a PC Card contains a battery to maintain

data stored within (i.e., volatile storage) Memory and I/O memory registers are digital scratch pads

where the card holds the data that can be accessed by the laptop


PC Cards A controller chip in the laptop links the PC

Card to the laptop when the PC Card is inserted.

When a PC card is inserted into a Laptop, the hardware detects that event and informs the operating system

The Operating system access the PC Card’s CIS to determine which PC Card is it and what device driver to load and initialize

The operating system assigns a memory address window and I/O register addresses and gives that to the card’s device driver

This memory window links the laptop’s memory to the memory area in the PC Card

Types of PC cards include modems, network cards, wireless LAN cards, cellular provider broadband cards, card readers, hard disks, etc.


PDAs Two Types

Palm - Palm OS Pocket PC - Windows Mobile (formerly CE)

Windows CE - compact version of Windows Color or Monochrome touch displays Ports (serial, USB, infrared, Bluetooth) Adapters for compact flash, secure digital, etc. Built-in functions (Word, Excel, Calendar, etc.) Volatile (RAM) & non-volatile memory (Flash)

Programs and data storage Early models use volatile memory

1996USR

2007HP


PDAs Input not great

handing writing recognition getting better small keyboard external peripherals available to augment I/O

Host PC wired connection of syncing and data interchange still vital

Wireless connectivity to host PC and services emerging

Compatibility with desktop applications a key importance of PDA success

New application: PDA + mobile phone


PDAsPDA Limitations: Battery operating life limited Battery loss means data loss if data in volatile

memory Not easily upgradable

quick obsolescence Less standardized than desktop PC Limited I/O Not meant to replace desktop!

Which to Choose: PDA or Portable Computer?


Future of I/O (end of Part 5 in book) Major hurdle for today’s computers

Man-machine interface (screens, keyboards, etc.) Key Evolutions

Speech recognition (voice commands to computer) Computer visual recognition Computer as active companion (monitoring temperature, brain

waves, screen phone calls, etc.) 3-D Holographic Displays Security Challenges

Authentication Privacy


Chapter 21: How Multimedia Sound Works


Sound Cards: Input A sound card (also referred to as an audio adapter)

receives analog electrical signals from the output of a microphone or other input device

A microphone is a device that converts sound into a proportional signal, much like photodiodes that convert light into a proportional electrical signal

The signals go to an ADC chip on the sound card that converts the analog audio signals into a stream of 1s and 0s

A ROM chip on the sound card contains instructions for handling the digital data at the output of the ADC


Sound Cards A sound card also contains a chip

called the Digital Signal Processing (DSP) chip

The DSP chip processes the digital signal based on instructions that are stored on the memory chip

Processing may involve compressing the digital information

The compressed file is then sent to the CPU which in turn sends the data to the hard disk for storage in a format such as .MP3 or .WAV


Sound Cards: Output A sound card also converts digital audio files into

analog electrical signals which it then feeds to the speakers of the computer

To play an audio file, the CPU fetches the file from either the hard disk, CD or from wherever it is stored

It then sends the file to the DSP for decompression The DSP in turn send the decompressed digital

information to the DAC chip which converts the digital information into an analog signal

The analog electrical signal is amplified and then sent to the speakers


MIDI and FM synthesis MIDI is short for Musical Instrument Digital Interface

(MIDI) In a MIDI file, only instructions on how to play the

audio file is stored, not the audio recordings themselves Instructions in MIDI files tell the DSP chip of the sound card

which instruments to play and how to play them A sound card has the capability of reproducing sound from

various instruments The different sounds of various instruments are stored in the

ROM chip of the sound card The DSP then fetches these various sounds based on

the instructions it receives


MIDI and FM synthesis The MIDI concept is analogous to storing the

notes of music instead of the music itself Instead of storing samples of the sounds, the

sound card may also store just the characteristics of the musical instruments such as their pitch (FM synthesis)

Based on these characteristics, the sound card may synthesize the sound

This does not produce as good quality music as storing the individual sounds on the ROM chip and using them to reproduce the music


MP3 MP3 is a popular audio compression

standard that has enabled the efficient sharing of music files

The reason that MP3 is so popular is because it provides a high degree of compression, yet maintains a good level of sound quality

MP3 perceptual coding: compression techniques discard the frequencies imperceptible to human the less prominent sounds that are “drowned

out” perceptually by more dominant sounds In addition to this lossy compression

approach, the MP3 format also applies a lossless compression algorithm exploits redundancies in information to

further compress information Analogous to a “ZIP” file

Conversion from a CD file to MP3 may be performed by a ripper (utility program)


iPod

Music on an iPod is stored mainly in two formats: MP3 or AAC Both are compressed formats

Stored along with each file is metadata that contains info about the artist name, album name, song category etc.

The number of songs that you can store depends on the size of the hard disk and how much each song has been compressed

You can store about 10,000 songs on an iPod with a hard disk of 40GB The iPod places the music file that is selected for listening in memory

instead of directly playing it from the hard disk This is because the song might skip if jostled in any way The memory chip does not contain any moving parts so the music will

not skip


Chapter 22: How Multimedia Video Works


Multimedia Video

A camera and a microphone capture picture and sounds and send the analog signals to a video card or also called a video-adapter card Video is merely a sequence of images (frames) that are captured by a camera

and shown in rapid succession together with sound An ADC on the adapter card converts the analog audio and video signals

into a pattern of 1s and 0s A compression/decompression chip compresses the information

Compression involves eliminating redundancy in each image that makes up the video

More space is saved by interweaving the picture and audio information within the same file or format called .AVI (audio/video interleave)


Multimedia Video To replay the video, the data is sent to the

decompression chip which restored the data that was eliminated during compression The combined audio and video elements are separated and

both sent to a DAC chip The DAC translates the digital information into analog signals

which are then sent over to the speakers and the screen Advanced compression techniques cut down on the

amount of data that must be recorded One method, used by .AVI format saves a complete video

frame and then records only the differences (called the delta) in the frames that follow

Each frame is recreated by combining the delta data with the data for the frame that preceded it


Multimedia Video Video on DVDs are stored in a compressed

format called MPEG (Motion Pictures Experts Group)

MPEG compressed by storing frame as Intraframe: complete data image for that frame Predicted frame: the difference between current

frame and last predicted frame or intraframe Bidirectional frame: using data from closest

frames, interpolates to get frame


TiVo TiVo is essentially a self-contained computer with a hard disk that

uses Linux The TV signal arriving from the coaxial cable feeds into the TiVo If the signal is in analog format, TiVo converts it into digital and

compresses it using MPEG The digital signal is then sent over to the hard drive

For viewing, the digital file is sent over to the decoder which converts it back into analog format for viewing

If someone wants to pause live television, TiVo stops playing the image on the screen but still continues to write the TV signal onto the hard drive Puts this into the live television buffer

When the play button is pressed, the stored file is retrieved from the hard disk and played on the screen

TiVo also enables the user to record programs


Homework #7 Write a 2 page essay comparing DSL

versus cable modems for residential use: Give a brief overview of each technology Discuss their advantages and disadvantages

compared to one another

gmu it 212 - spring 20071 displays, i/o, portable computers, multimedia it 212 002 how computers...

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