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Part 1 Major Concepts


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Title: Part 1 Major Concepts

Part 1 Major Concepts
  • Hardware inside the PC
  • 5 Elements of a computer
  • POST
  • Disk boot
  • Interrupts
  • Plug and Play

Hardware Inside the PC
  • Power Supply
  • Case
  • Removable Drive
  • CD-ROM Drive
  • Tape Drive
  • Hard Drive
  • Floppy Drive

Hardware Inside the PC
  • IDE Controllers
  • AGP Expansion Slot
  • PCI Expansion Slot
  • Video Card
  • Sound Card
  • RAM
  • Real-Time Clock

Hardware Inside the PC
  • CMOS Complementary Metal-Oxide Semiconductor
  • BIOS Basic Input-Output System
  • CMOS Battery
  • Microprocessor
  • Heat Sink
  • Fan

Hardware Inside the PC
  • USB ports
  • Mouse Port
  • Keyboard
  • Parallel Port
  • Serial Ports
  • Sound Card Connections
  • Modem

5 Elements of a Computer
  • Input
  • Output
  • Memory
  • CPU
  • Storage

  • Sound Card
  • Speaker output
  • Microphone line inputs
  • Modem (MOdulator/DEModulator)
  • Ports (USB, Parallel, Serial, SCSI)

  • Keyboard
  • Mouse/Trackball/Touchpad/Wireless/programmable/poi
  • Originated by Xerox Palo Alto
  • Touch screens

  • Video Card (AGP)
  • Powerful computer in its own right
  • Display (monitor)
  • Resolution
  • Refresh Rate
  • Bandwidth

Electronic Memory
  • L1 Cache (on microprocessor chip)
  • L2 Cache (on motherboard)
  • RAM (on motherboard or daughter board)

CPU Control and ALU
  • Microprocessor
  • Real-time clock
  • BIOS
  • CMOS
  • IDE Controller
  • SCSI Controller
  • USB Controller

Power-On Self-Test
  • Boot (Boot Strapping)
  • Steps computer takes to get from your pushing
    on button to when the computer is operational
  • First Step Power On Self Test (POST)
  • Purpose Computer tests itself to ensure that
    basic processing unit and connected devices are
    alive and well
  • Test Result
  • Pass single short beep
  • Failure different combinations of beeping
    (including no beep at all), displays messages, if

How Does POST work?
  • When Power Is Turned On, Electrical Signal Is
    Sent to CPU Signaling It to Reset
  • Clears old data, initializes counters (registers)
  • Sets program counter to pre-defined address in
    memory (F000)
  • Memory location referenced is in Read Only Memory
    (ROM) of PCs Basic Input/Output System (BIOS)
  • ROM stays the same, even when we turn off the
  • Instructions define steps CPU should perform to
    complete self test

Self Test Steps
  • CPU Checks Itself (e.g., adds some numbers,
    checks results)
  • Sends Electrical Signals Over Bus to See If All
    Components Connected to Bus Are Functioning
  • Check System Timer (Real-time Clock)
  • Check Out memory on Video Card
  • Locate card, execute video card POST
  • If passes, link video card to CPUs BIOS
  • If all goes well, display text/graphics

Self Test
  • Check Out RAM (volatile memory)
  • Write data to each chip
  • Read stored data is it what was written?
  • Detect how much memory is available

Self Test
  • Establish What Disk Drives Are Available
  • Verify Keyboard, Have Any Keys Been Pressed?
  • Now That Post Is Complete…
  • Components are functioning properly
  • Have located disk drives

Self Test
  • Check Out Remaining Components
  • See if component contains own BIOS code
  • If so, execute startup code, link to BIOS
  • See if component supports Plug and Play
  • execute Plug and Play instructions to distribute
    system resources
  • Compare Component Inventory With Saved List
  • Stored in CMOS chip
  • If different given choice is this new list

Disk Boot
  • Task
  • Objective load operating system, which includes
    software to access disks into memory
  • Problem how do I load from a disk the software
    that tells me how to use a disk if I dont know
    how to access the disk in the first place?
  • Key players
  • BIOS (in EPROM) (will link to operating system)
  • CPU (brains)
  • Disk drive, contains disk operating software
  • RAM (final resting place for software)

Disk Boot 1
  • BIOS checks floppy disk drive. If present, checks
    predefined location on floppy for disk operating
    system files (IO.SYS and MSDOS.SYS)
  • If not present in floppy, checks hard drive
  • If not present on hard drive, generate error
  • Order of reading devices can be changed in BIOS

Disk Boot 2
  • Boot program reads first sector of disk (cylinder
    0, head 0, sector 1) (512 bytes) Master Boot
    Record (MBR)
  • MBR is a miniprogram that locates bootable
    partition of the disk
  • BIOS transfers control to MBR
  • MBR locates DOS boot record (DBR), also a

Disk Boot 3
  • DBR attempts to load hidden file IO.sys into
  • If OK, DBR transfers control to SYSINIT, a
    program within IO.sys
  • At this time boot record is no longer needed and
    can be erased from RAM.

Disk Boot 4
  • SYSINIT loads MSDOS.sys into RAM
  • File management
  • How to execute programs
  • Interact with hardware
  • SYSINIT locates CONFIG.SYS (at root directory)
  • User defined
  • Lets user tailor operating system
  • Loads certain device drivers

Interrupt Handling
  • When an Event Occurs, a Hardware Signal Is
    First Sent to the Interrupt Controller Chip That
    Detects and Interprets the Interrupt
  • Interrupt Controller Chip Notifies CPU That
    Interrupt Has Occurred
  • Since the CPU Was Doing Other Things, the
    Processor Saves Its Current State So That It Can
    Resume That Task Later (Pushes Data Onto the

What is Plug and Play? 1
  • So whats the problem?
  • Each PC Contains a Number of Components That Need
    to Work Together
  • Each Component May Need to Have Its Own
  • Interrupt ID
  • RAM that only it writes to (DMA)
  • Input/Output address (e.g., floppy drive vs. hard
  • ROM address (where its own BIOS will go)
  • RAM buffer address (how data is passed to/from
    this component)

What is PP? 2
  • This Cooperation Depends on the Exact
    Configuration of Components
  • Each Time a Component Is Added or Taken Away, the
    Configuration Must Be Changed
  • Plug and Play Is a Standard Which Allows Your
    Computer to Perform This Task Automatically,
    Letting You Use You New Components Without Time
    or Error Potential of Performing Your Own

How Does Plug and Play Work? 1
  • Plug and Play Compatible BIOS Locates All
    Potential Components (Plug and Play Compatible)
  • Each component contains a unique identifier as
    part of its Read Only Memory (non-volatile
  • Each component defines what resources it needs
    and what range of resources it will accept
  • BIOS transfers control to operating system

How Does PP Work? 2
  • Windows Configuration Manager Creates Enumerators
    (Interface Programs Between Operating System and
    Devices Themselves) Based Upon Located Interfaces
  • ISA enumerator
  • SCSI enumerator
  • Port enumerator

How Does PP Work? 3
  • Enumerators Consolidate Information for All
    Components Using a Given Interface and Provide
    This to the Configuration Manager
  • Configuration Manager Assigns Actual Resources
    (e.g., Interrupt IDs), Avoiding Conflicts. Each
    Component Stores These Assignments Within Its Own
    Hardware So That It Knows How It Will Be Used
  • OS Locates Driver for All Components If Not
    Found, Asks User to Install It

Part 2 Major Concepts
  • How programming languages work, different
    programming languages
  • Windows multi-tasking
  • Manipulators of data
  • Bitmapped graphics, compression, vector graphics
  • Resolution
  • Computer security definitions
  • Viruses, anti-virus software

How Programming Languages Work
  • Software is created using different computer
    programming languages that provide instructions
    for telling computers what to do
  • Unlike the English language, which is less than
    precise, computer language is more exacting and
  • Different programming languages for different
    types of computers and tasks
  • Usually described as low-level or high level

Different Programming Languages
  • Low-level versus high-level languages
  • The more a computer language represents English,
    the higher its level
  • Low-level- machine language a series of codes
    represented by 1s and 0s
  • Communicate directly with the PCs processor
  • Assembly Language
  • Slightly higher than low-level language, uses
    simple command words to supply step-by-step
    instructions for the CPU to carry out

Different Programming Languages - 2
  • High-level languages allow programmers to write
    in words and terms that more closley parallel
  • Java
  • C, C
  • XML
  • Highest level languages
  • BASIC Beginners All-Purppose Symbolic
    Instruction Code
  • Visual Basic key many key words and phrases that
    execute specific commands within the program when
    it is compiled run

Multitasking Under OS Control
  • Running several application programs at the same
  • Doing a web search while typing in your homework
    on your word processor
  • What problems does this create?
  • Only 1 CPU (processor)
  • Memory
  • Use must be coordinated
  • May run out of RAM in MS Windows

Windows Multitasking (Memory)
  • Each application is assigned a block of RAM for
    its exclusive use
  • As allocated RAM fills up, OS swaps out unused
    pages of RAM to virtual memory on disk
  • If swapped-out pages are needed later, they must
    be swapped back into RAM, from slower virtual

Windows Multitasking (CPU)
  • Each program is given a very short slice of time
  • Not interrupt driven
  • When time is up
  • CPU internal registers used by the application
    are saved
  • CPU internal registers used by the other
    application are restored

Windows Multitasking (Peripherals)
  • If application program wants to use a peripheral,
    it queries the OS
  • If free, OS connects application to peripheral
    (e.g., prints document)
  • If not free, OS rejects request, or, e.g.,
    queues file to print and prints when free

Manipulators of Data (1)
  • Database managers
  • Address list
  • Digital juke boxes
  • Word processing
  • Including desktop publishing
  • html editors

Manipulators of Data (2)
  • Number crunchers
  • Spreadsheets
  • Financial packages
  • Graphics
  • Drafting programs (CAD)
  • Paint programs
  • Photo editing

Manipulators of Data (3)
  • Multimedia
  • Combines pictures, music, spoken words
  • Communications software
  • E-commerce, broadcasting, email
  • Encryption
  • Utilities
  • Virus checkers
  • Compression

Bitmapped Graphics Files
  • File starts with information
  • Which bitmapped graphics format it is in
  • .BMP, .PCX, .TIF, .JPG
  • Magic number
  • The height and width of the picture in pixels
  • The palette
  • Number and range of colors which can be used in
    the image

Bitmapped Graphics
9 Pixels
9 pixels
  • Bitmapped Graphics
  • A format in which each pixel is individually
  • Binary
  • Black/white
  • Color
  • Red/Green/Blue (RGB) various resolutions

Bitmapped Graphics Color
  • Instead of black and white, each pixel can be a
    different color
  • Accuracy of color depends on how many different
    colors we can represent
  • Select from predefined palette of colors (2, 64,
    or 256)
  • Specify the amount of red, blue, and green in
    each pixel
  • Permits 16,777,216 million colors (256 256
  • Describing each pixel takes 24 bits (vs. 8 for
    256 colors)

  • Describing all these pixels in so many colors can
    take up a lot of space
  • More file space
  • More RAM to display
  • More time to see web page
  • More time to ftp data over communications link

Compression (1)
  • To reduce storage requirements, use data
    compression techniques
  • Lossless
  • Reduce data quantity without loss of information
  • Scientific uses, e.g., space imagery from Mars
  • Lossy
  • Reduce data quantity, but loss of quality
  • JPEG, reduce quantity with minimal loss of quality

Compression (2)
  • Detect presence of patterns within data
  • Observation consecutive pixels are often same
  • Use run-length encoding (RLE)
  • Check first bit of key byte
  • if 1, next 7 bits define how many subsequent
    bytes will describe individual pixels
  • if 0, next 7 bits define how many subsequent
    bytes will have the identical color value
  • RLE great when consecutive pixels are same, can
    actually require more storage if all pixels are

Displaying Bitmapped Graphics
  • Video Graphics Adapter Card
  • Stores image in video memory
  • Controls position of beam on screen
  • Uses digital to analog (D/A) converter chip to
    convert digital representation of hue,
    saturation, and intensity (HSI) into electrical
    signal fed to monitor to write each pixel
  • Screen consists of red, green, and blue phosphors
    which phosphoresce at varying intensities to
    create color.

Vector or Bitmapped Graphics
  • Vector graphics
  • Line is an object represented as formula
    containing start/stop point, width, line and fill
    colors, hierarchy
  • Easily rotated, stretched, flipped, resized and
  • To display object on monitor, program creates a
    temporary bitmapped image using the resolution
    defined for this display device

Vector or Bitmapped Graphics
  • Consider drawing a red line via graphics creation
  • Paint (bit mapped graphics)
  • Fixed number of pixels form the entire line
  • Not easily enlarged or reduced

Creating graceful curves is easy with Draw
programs can control exactly the location and
degree of curvature
  • We can also control how many pixels we use to
    represent the picture

Gray Scale 7,000
LineArt 1,000
150 DPI Color 88,000
72 DPI Color 21,000
Computer Security Definitions NSA
  • Virus
  • A program that can infect other programs by
    modifying them to include a possibly evolved,
    copy of itself.
  • Trojan Horse
  • An apparently useful and innocent program
    containing additional hidden code which allows
    the unauthorized collection, exploitation,
    falsification, or destruction of data

Definitions NSA
  • Tinkerbell Program
  • A monitoring program used to scan incoming
    network connections and generate alerts when
    calls are received from particular sites, or when
    logins are attempted using certain IDs
  • Back door
  • A hole in the security of a computer system
    deliberately left in place by designers or
    maintainers. Also trapdoor.

Definitions NSA
  • Hacking
  • Unauthorized use, or attempts to circumvent or
    bypass the security mechanisms of an information
    system or network
  • Letterbomb
  • A piece of email containing live data intended to
    do malicious things to the recipients machine or

Typical Virus Approach (1)
  • Replication to infect others
  • Virus copies itself into the beginning of
    programs that a user typically runs
  • Virus copies itself to disk boot record
  • Camouflage to avoid detection
  • Change itself so that detection software cannot
    identify it by a unique signature
  • Distort file size information so that additional
    virus code is not detected

Typical Virus Approach (2)
  • Event watching
  • Executing in background, virus continually checks
    for a specific event to occur (e.g., specific
  • Delivery
  • Display message, delete files, corrupt files, etc.

How does a computer get infected?
  • Embedded in master boot record of stranger disk
  • Embedded in new executable software
  • Embedded in a mail message
  • Typically a program within mail message
  • Can also be a macro within a data file such as MS
    Word document

Antivirus Actions
  • Check all locations where virus may reside
  • Master boot record
  • Program files
  • Macro code
  • Signature Scanners
  • Check for exact match of program instructions

Antivirus Actions
  • Heuristic Detectors focus on typical behavior of
  • Memory resident
  • Continually running on computer
  • Intercedes when unsafe operation
  • Downloading files from Internet
  • Copying files
  • Another program tries to stay resident in memory

Part 3 Major Concepts
  • Transistors
  • RAM
  • Logic Gates

How a Transistor Works
  • Thousands of transistors are connected on a
    single slice of Silicon
  • The slice is embedded in a piece of plastic or
    ceramic with the ends of the circuitry attached
    to metal leads that reach out to connect to other
    parts of the computer circuit board
  • The leads carry signals to the chip and send
    signals form the chip to other components

How a Transistor Works
  • The transistor is the basic building block from
    which all microchips are built
  • It can only create binary information, a 1 if
    current passes through it, a 0 if current does

How a Transistor Works
  • PCs based on the the first Intel 8088 and 80286
    processors were 16 bit PCs
  • They could work with numbers of up to 16 bits in
    length, or a decimal number of 65,535
  • Current PCs are 32 bit capable and work with
    numbers that are 32 bits wide, the equivalent of

How a Transistor Works
  • Transistors can just as easily represent a true
    or false condition
  • Transistors in various combinations form Logic
  • Logic Gates are combined into arrays to form Half
  • Half Adders are combined to Full Adders
  • More than 260 transistors are needed to create a
    full adder capable of handling mathematical
    operations for 16 bit numbers

How a Transistor Works
  • A small positive charge is sent down an aluminum
    lead that runs inside the transistor
  • The charge spreads to a layer of conductive
    polysilicon buried in the middle of
    non-conductive silicon dioxide
  • Silicon Dioxide is the main component of sand

How a Transistor Works
  • The positive charge on the aluminum attracts
    negatively charged electrons out of the base of
    the transistor made of p-silicon creating a
  • On one side of the transistor exists a Source
    lead that fills the vacuum created by the rush of
    negatively charged particles with additional
    negatively charged particles
  • The electrons from the source also flow toward a
    similar conductive lead called the Drain

How a Transistor Works
  • The rush of electrons completes an electrical
    circuit turning the transistor on which
    represents a 1 bit.
  • If a negative charge is applied to the
    polysilicon, the negatively charged electrons
    will repel each other and the transistor will
    remain off and represent a 0 bit

How RAM Works
  • Before a PC can do anything it must move data
    from disk to RAM
  • Data contained in documents must also be stored
    in RAM if only for a fraction of a second before
    it moves to the processor for computation
  • Every PC is a collection of switches representing
    a 1 or a 0 which represent every piece of
    data that runs on your PC
  • RAM is blank upon energizing the PC, becomes
    filled with 1s and 0s when you turn off your
    PC, the contents of RAM is lost

How data is Written to RAM
  • Think of the inside of your PCs RAM like a
    collection of switches connected by microscopic
    electrical circuits called Address Lines
  • Software, in combination with the OS is
    continually sending tiny bursts of electrical
    current along Address Lines
  • Each Address Line identifies locations of spots
    where data can be stored

How Data is Written to RAM
  • The electrical pulse turns on or closes a
    transistor thats connected to a Data Line at
    each memory location where data can be stored
  • While transistors are turned on, software
    continuously sends bursts of electricity along
    selected data lines
  • Each burst represents a 1 bit to a transistor

How Data is Written to RAM
  • Where a transistor is turned on, the burst of
    electricity serves to charge a capacitor which
    stores electricity and keeps the 1 bit stored in
    the transistor
  • Each charged capacitor represents a 1 bit
  • Each uncharged capacitor indicates a 0 bit
  • Capacitors will eventually lose their charge if
    not refreshed regularly

How Data is Read From RAM
  • When software wants to read data from RAM,
    another electrical pulse is sent along the
    address line, closing the transistors connected
    to it
  • At each address line where there is a charged
    capacitor, the capacitor will discharge via the
    circuit created by the closed transistors sending
    electrical pulses along the data lines
  • Software recognizes which data lines the pulses
    come from and interpret each pulse as a1
  • Any line lacking a charge is interpreted as a 0

Types of Logic Gates
  • NOT Gate
  • Made of a single transistor
  • Designed to take input from the clock and from
    another transistor
  • Produces a single output, always opposite from
    the input of the transistor If current from the
    transistor representing a 1 is sent to the NOT
    gate, the NOT gates own internal transistor will
    switch open and stop the flow of current, and
    make the output from the NOT gate a 0

NOT Gate
  • If the current from the transistor representing a
    0 is sent to the NOT gate, the NOT gates
    internal transistor closes producing the output
    from the NOT gate of 0
  • NOT gates strung together produce other logic

Input bit
Clock Pulse
Output bit
OR Gate
  • OR gates create a 1 if either the first or second
    input is a 1
  • Create a 0 if both inputs are 0

AND Gate
  • AND gate outputs a 1 only if both the first and
    the second inputs are 1s

XOR Gate
  • XOR gate puts out a 0 if both inputs are 0 or if
    both are 1
  • Generates a 1 only if one of the inputs is 1 and
    the other is 0

Combinations of Logic Gates
  • Different combinations of logic gates make
    computers able to perform all math of all
  • Accomplished through half adders full adders
  • Half Adder
  • Consists of an XOR gate and an AND gate both of
    which receive the same inputs representing a 1
    digit binary number
  • Full Adder
  • Consists of half adders and other switches
  • Combinations of a half adder and a full adder can
    handle large binary numbers

Part 4 Major Concepts
  • Chapters 10-12
  • Electromagnetism
  • Reading/writing files
  • Disc formatting
  • Disc compression, file compression
  • Disc defragging

  • Conductivity
  • The ability of a material to conduct electrical
  • Some materials are more conductive than others
    and lose electrons in the outer most layer of the
    atom more freely compared to others
  • Non-conductive
  • Do not conduct electrical current, do not lose
  • Also known as insulators

  • Each electrical device creates stray unwanted
    electromagnetic fields called noise
  • Computers are designed to eliminate or reduce
    noise because of its negative impact on PC
  • Nonconductive wires added to cables
  • Insulators around items that create large amounts
    of noise
  • More noise makes it necessary to increase the
    electrical power to get signals pushed through
  • Stronger signals create more noise

  • When a wire moves through a magnetic field, the
    interaction creates an electrical current inside
    the wire
  • We will see that this is the basis of how
    read/write heads inside floppy drives and hard
    drives operate

  • Electromagnetic (EM) Radiation Spectrum
  • Includes the complete range of energy beginning
    with the longest radio waves through visible
    light and including rays produced by radioactive
  • All energy in the EM spectrum expands in waves at
    the speed of light
  • Electromagnetic fields are measured in terms of
    their frequency the number of times a wave is
    produced in a period of time, usually 1 second
  • Measured in hertz

  • Frequency in an EM field is inversely related to
    its wavelength
  • Wavelength the distance between two identical
    points in adjacent waves
  • The higher the frequency of the signal, the
    shorter the wavelength
  • The lower the frequency of the signal, the longer
    the wavelength

  • Electromagnetic fields are used as signals to
    carry data by varying the waveform
  • Frequency Modulation
  • Carries data by varying the frequency of a
    waveform the number of times a waveform repeats
    itself in a measure of time
  • Amplitude Modulation
  • Carries data by varying the amplitude or height
    of a waveform

Writing and Reading Bits to a Disk
  • Before data is stored on disks, microscopic iron
    particles are scattered in random order
    throughout the disk surface
  • To organize the particles, electricity pulses
    through a coil in the read/write head creating a
    magnetic field that magnetizes the particles on
    the disk
  • This arranges the particles with their positive
    poles pointing toward the negative end of the
    read/write head and the negative poles pointing
    toward the positive end of the head

Writing and Reading Bits to a Disk
  • Bands of aligned magnetized particles are created
    in succession as the disk spins
  • Two bands are created to represent the smallest
    discrete unit of data, a single bit
  • A binary 1 is created by swapping the orientation
    in two bands of particles
  • This aligns like ends next to each other in two
  • A binary 0 is created by orienting two bands of
    particles identically in the same direction

Writing and Reading Bits to a Disk
  • To store a second bit, the polarity of the first
    band is always opposite of the band preceding it
    to indicate that its beginning a new bit
  • To read data, no current is sent to the
    read/write head
  • As the disk platter spins, the particles
    themselves create a magnetic field that generates
    current that travels in one direction or the
    other through wires leading from the head

Writing and Reading Bits to a Disk
  • The direction of the current traveling through
    the head depends on the polarities of the bands
  • By sensing changes in the direction of the
    current coming from the disk, the CPU can tell if
    the data is a 1 or a 0

Formatting a Disk
  • Before any disk can have material stored on it,
    it must be Formatted
  • Formatting organizes the disk so the the same way
    every time so any PC can store and retrieve data
    from any formatted disk
  • Each disk is divided radially in sectors which
    are similar to a slice of pie
  • Each disk also contains concentric circles called

Formatting a Disk
  • Cluster
  • Two or more sectors on a single track
  • Cluster is the minimum unit the operating system
    uses to store information
  • The number of sectors, tracks, and clusters that
    a drive can create on a disks surface determine
    the capacity of the disk

Formatting a Disk
  • File Allocation Table FAT or VFAT in Windows
  • A special file located in sector 0 of the disk
  • VFAT made large file names possible due to its
    ability to store 255 characters
  • Also where the operating system stores
    information about a disks directory or folder
    structure, and what clusters are used to store
    which files
  • Windows 98 introduced FAT32 allowing hard drives
    larger than 2 GB to be formatted as a single disk

Disk Compression
  • Prior to disk compression files were saved to
    clusters but did not store data in the cluster in
    the most efficient manner
  • Given a cluster size of 8KB a file 18KB in size
    would take 3 full clusters to store
  • Clusters were used as all or nothing storage
  • In the example above the first 16KB of the file
    are stored neatly into 2 clusters, and the
    remaining 2KB are stored in a single 8KB cluster
    but leave 6KB free and unusable by other files

Disk Compression
  • Compressed Disks get more effective use of
    storage by creating a single file on the drive
    known as a compressed volume file or CVF
  • A CVF is treated by the OS as if it were a drive
  • When the OS writes a file to the CVF, it uses
    only as much of a cluster as it needs
  • Each file is separated by a very small space of
    blank disk space

File Compression
  • File Compression, also know as zipping a file
    reduces the size by eliminating redundancies in
    the file
  • Known as lossless compression because every bit
    in the file can be restored exactly as it was
    originally written
  • The compression uses a algorithm called an
    adaptive dictionary-based algorithm

File Compression
  • The compression program reads the file and looks
    for recurring patterns of data
  • When a pattern is identified, it writes the
    pattern to a dictionary instead of writing the
    pattern in the line where it exists
  • The dictionary is then stored as part of the
    compressed file

File Compression
  • Where the pattern would have been written the
    program places a pointer that tells where the
    omitted pattern is located in the dictionary
  • When a compressed file is read, pointers are
    encountered and compressed files are read on the
    fly by retrieving the file and writing it to RAM
  • File types are directly related to how much it
    will shrink during compression

Disk Defragging
  • When the first file is saved to a disk, it is
    saved on a track in clusters that are contiguous
  • This means that the file is stored in one
    continuous stream of clusters
  • Over time, as files are erased, empty clusters
    are left behind
  • These clusters are seldom contiguous

Disk Defragging
  • Since a file may not fit neatly into one or more
    clusters, they are stored in many clusters that
    are not contiguous
  • Files are written to many clusters in many
    locations in other words, files are fragmented
    into many clusters throughout the disk

Disk Defragging
  • Fragmentation slows down the drive due to the
    constant seeking the read/write heads must do to
    track down all parts of a file
  • Defragmentation is a software controlled
    operation that moves scattered parts of files
    into contiguous clusters

Disk Defragging
  • Defragging begins by moving contiguous clusters
    of data to other unused parts of the drive
  • This opens large areas of contiguous space
  • The drive then moves fragmented parts of a file
    into the newly opened space and stores them in a
    contiguous manner
  • The process continues until all files possible
    are stored in a contiguous manner

Part 4 Major Concepts
  • Chapters 13-14
  • CD-ROM technology
  • CD-R discs
  • DVDs
  • CD-RW and DVD RAM

Optical Storage
  • Optical Storage Media
  • CDR
  • CDRW
  • DVD
  • All use a similar technology, just slightly
    different variations

CD-ROM Drive
  • The beam penetrates the protective layer of
    plastic and strikes a reflective payer that looks
    like aluminum
  • The surface of the disc is made up of high and
    low spots called lands and pits
  • Lands are flat areas
  • Pits are tiny depressions
  • These two surfaces are a record of the 1s and 0s
    used to represent data to the PC

CD-ROM Drive
  • Light that strikes a pit is scattered and not
    sent back to the detector
  • Light that strikes a land is reflected directly
    back to the detector and passes through a prism
    and to a light-sensing diode
  • Each pulse of light generates a small electrical
  • Each voltage is matched against a timing circuit
    to generate a stream of 1s and 0s

CD-ROM Drive
  • On a CD-ROM disc, data is contained in a single
    track that spirals in a track from the center to
    its circumference
  • Each track is divided into sectors, but each
    sector is the same size opposed to a metal disc
    where the size of the sector varies with distance
    from the center of the disc
  • Using Constant Linear Velocity the disc drive
    constantly varies the rate that the disc spins at

CD-ROM Drive
  • Therefore, as the detector moves toward the
    center of the disc, the disc must speed up
  • This roughly equates to more sectors, more data

CD-R Discs
  • Dye layer is designed to absorb light at specific
    frequency, the frequency of the laser beam
  • As it absorbs light, it creates a mark on the
    disk in one of three ways
  • By bleaching the dye
  • By distorting the dye
  • By making the dye bubble
  • Regardless of how the mark is created, the result
    is a distortion called a stripe along the spiral
    track of the disk

How a DVD Works
  • One or two sides?
  • Layers of a DVD
  • Polycarbonate plastic
  • Opaque reflective material
  • Transparent film
  • Protective plastic

How a DVD Works
  • Data is represented by a series of lands and
    pits, similar to a CD-ROM but much smaller
  • Lands and pits are formed on two layers of the
    DVD opposed to one on the CD-ROM
  • DVDs use lasers to read data
  • Shorter wavelength makes the beam able to read
    smaller lands pits on the DVD

How a DVD Works
  • Beams are reflected back by lands and scattered
    by pits, similar to CD-ROMs
  • Data is created in the same manner
  • Reflection creates electrical pulses
  • Scattered light does not send any energy back to
    the prism
  • By changing the amount of current flowing through
    the magnetic coil surrounding the laser beam,
    DVDs focus the beam so its concentrated on the
    surface of the transparent film or is sent deeper
    to the opaque layer

How a DVD Works
  • Spiral tracks are also recorded in two layers and
    each goes in a different direction
  • One spiral starts a the edge of the DVD and goes
    to the center
  • The read head follows the track into the center
    of the disc
  • The other track is recorded in the opposite
    direction on a different layer
  • When the read head reaches the center, it then
    traces the other spiral outward to the edge

  • CD-RW Re-writeable Compact Disc
  • DVD-RAM Re-writeable DVD
  • Both use a process called Phase change technology
    to write, change and erase data

  • Recording layer is typically made of a
    crystalline silver, indium, antimony and
    tellurium compound embedded in the disc
  • The laser beam selectively heats areas to
    900-1,300F degrees
  • Where the beam strikes, the heat melts the
    crystals to a non-crystalline amorphous phase
  • These areas reflect less light
  • The read beam consists of a weaker stream of
    current strikes a non-crystalline area and is
    scattered and not picked up by the read head

  • A process called the annealing phase erases the
    data on the disc
  • Uses a beam of 400F to melt the that the
    compound returns to its crystalline state
  • The beams that are used by each type differ in
  • DVD-RAMs are are able to read and write data in a
    more compact manner, which makes them able to
    store more data in the same size area as a CD-RW

Part 5 Major Concepts
  • Chapters 15-16
  • Energy to data
  • Analog and digital conversion
  • Scanners, digital cameras
  • Power supply's
  • How AGP works

How Energy Turns Into Data
  • Perceptions are analog one continuous wavy line
    of events moving at predictable rates
  • But really things are more digital discrete
    separate events with different numerical values
  • Digital to Analog Converters DACs and Analog to
    Digital Converters ADCs handle all conversions
    to and from each form of data
  • Charged-Coupled Devices turn light into
    electrical energy
  • Light is turned into electrical energy

Analog and Digital Converters
  • Visible light and audible sound both travel in
  • The brighter the light, the more electrical
    current it can be converted into
  • The louder the sound, the more electrical current
    it can be converted into
  • Computers convert all analog input into digital
    values it can use
  • The opposite conversion must also take place upon
    sending digital data to output devices

Analog Converters
  • Analog to Digital Converters constantly sample an
    analog signal sent to it in the form of a
    wavering current
  • Each time the current is measured, it is assigned
    a number that represents its value at the moment
    it was recorded
  • Usually used for collecting input in the form of
    sound or light

Digital Converters
  • Digital to Analog converters changes a string of
    digital values into rapidly changing voltages
  • Current is sent along different patterns through
    resistors resulting in an analog stream of
    current that varies to correspond to digital data
  • Usually used for output

Digital and Analog Conversion
  • Precision is affected by how often the analog
    signal is sampled
  • More samples detect finer changes in the signal
  • Precision is also affected by the sensitivity of
    the sensors

Digital and Analog Conversion
  • Resolution with respect to DAC and ADC is the
    range of values and amount of information that a
    device can hold for one sample
  • Resolution depends on the bits a device can
    devote to a digital translation of the analog

Digital and Analog Conversion
  • If a DAC has only one bit to represent a sample
    of an analog signal it can only show whether the
    analog signal is on or off, black or white
  • If a DAC has 16 bits to express each digital
    sample it can represent 256 shades of red
  • Higher the resolution number, the higher the
    definition in either sound or color

How Scanners and Digital Cameras See
  • Scanners and digital cameras have to convert
    different amounts of light into corresponding
    energy levels, and eventually 1s 0s
  • Both use a charge-coupled device CCDs to solve
    the problem
  • A camera must divide light passing through the
    lens into green, red, and blue elements
  • It must also register the light that falls at the
    same moment on a very small area the size of 2
    postage stamps

How an Uninterruptible Power Supply Works
  • Two types
  • Offline
  • Online

How an Offline Uninterruptible Power Supply Works
  • Offline or passive UPSs split incoming current
    into two branches
  • One feeds the normal power of the PC
  • The other passes through a battery charger which
    changes the current from AC to DC to keep the
    battery charged
  • If power fails, within 4-20 milliseconds the
    microprocessor inside the the UPS closes a switch
    that sends DC through an inverter and turns the
    batterys DC current into AC needed by the PC

How an Online Uninterruptible Power Supply Works
  • Online or serial UPSs feed all current through an
    AC-DC converter, from there to a battery, then to
    an inverter and then to the PC
  • This way, the UPSs battery is always charged and
    supplying current to the PC
  • If power fails, a microswitch breaks the
    connection between the wall and the UPS and
    current flows from the battery

How AGP Works
  • AGP chipset replaces the PCI bus input/output
  • Coupled with a Pentium 4 chip and RDRAM memory
    capable of 3.2GB/sec data transfer
  • Handles transfers of data among memory, CPU and
    the ISA controller all simultaneously
  • Also handles transfers to the PCI local bus at

How AGP Works
  • The AGP chipset puts the AGP port on the same
    part of the bus as memory, with data transfers of
    up to 1056MB/sec between those items
  • The arrangement allows AGP accelerated graphics
    adapter to replace the adapter on the PCI bus
  • Eliminates the need for video RAM
  • Provides faster Direct Memory Access enabling
    some to read/write to memory without the help of
    the CPU
  • Sends four bursts of 32 bits of data with every
    clock tick equaling 1056MB/sec data transfer to
    and from RAM

Part 5 Major Concepts
  • Chapters 17-19
  • Port Types
  • Peripherals
  • Keyboards
  • Displays
  • VGA
  • LCD
  • DLP

Types of Common Ports
  • Parallel
  • Serial
  • IDE
  • USB
  • SCSI

How a Parallel Port Works
  • 25-36 pin connection
  • PC side has 25, printer side has 36 with a
    different connector on each end
  • Parallel ports can send several bits of data
    across eight parallel wires simultaneously
  • Similar to a formation of soldiers
  • Think of a platoon of soldiers marching 8 abreast
  • When the platoon reaches a line on the ground, 8
    soldiers cross the line at one time, followed by
    the next 8 and so on
  • Faster than serial ports

How a Serial Port Works
  • Think of soldiers in a single file line, one
    behind another
  • When the soldier reaches a line on the ground, he
    and only he can cross at one time, then the next,
    the next and so on
  • Different than the 8 simultaneously crossing on
    the parallel port
  • Slower than parallel port

Universal Serial Bus USB
  • USB cable contains 4 wires
  • 2 for electrical power
  • 2 for sending data and commands
  • Two speeds of data transfer via USB cable
  • High speed 12Mbs megabits a second
  • Used for monitors, scanners, printers
  • Low speed 1.5Mbs
  • Used for keyboard or mice
  • Serial ports send 100kbs
  • Parallel ports send 2.5Mbs

Universal Serial Bus USB
  • Cables can connect to a USB hub capable of
    connecting to many other USB devices
  • Expands the 2 ports on the PC to many more
  • Each USB device can act as an extension to
    another USB device e.g. from a hub to a monitor,
    to speakers, to a keyboard and so on, up to 127

IDE Connections
  • Each of the connections can connect to a hard
  • E-IDE can control floppy drives, CDROMs, and tape
  • Devices must be E-IDE compatible and mounted
    inside the PC
  • For each pair on a single cable, one device is
    master and the other is slave
  • This serves as a traffic light for signals
    destined for one or the other

Small Systems Computer Interface SCSI
  • Last device in the daisy chain must have a
    terminator to provide a ground for the port not
    used in the last device
  • Cable is a flat ribbon cable with 50 lines
  • Two speeds of data transfer
  • Most common, 8 lines used to send data
  • Capable of 10-20MB second

Small Systems Computer Interface SCSI
  • Wide SCSI uses a 16 bit path, capable of 40MB
  • All data transfer managed by the SCSI controller
    card inside the PC
  • Each wire of the ribbon cable has a specific
  • Some are for specific bits in a byte 0 bit
    parity bit
  • Some are command lines that send specific
    commands like BSY, ANT, ACK

How a Keyboard Works
  • When you press a key, you create a change in the
    current flowing through a circuit associated
    specifically with that key
  • A microprocessor in the keyboard detects the
    increase and decrease in current from the key
    that was pressed
  • Detecting both an increase and decrease, the
    processor can tell when the key was pressed and

How a Keyboard Works
  • Each key has a unique set of codes
  • Processor can distinguish between the left and
    right shift keys
  • To distinguish real signals from an aberrant
    current fluctuation, the keyboard is scanned
    hundreds of times per second
  • Depending on which key is pressed, the processor
    will generate a scan code

Super VGA Display
  • Adapter sends signals to three electron guns
    located in the back of the monitors cathode ray
    tube CRT
  • Gun shoots 3 streams of electrons
  • One for each of the 3 primary colors
  • Intensity controlled by the signals from the
  • Adapter also sends signals to the magnetic
    deflection yoke
  • This focuses and aims the electron beams
  • Signals also help determine the resolution of the
    monitor number of pixels horizontally and
    vertically and the refresh rate how frequently
    the screen is redrawn

Super VGA Display
  • The electrons from the gun strike phosphors on
    the inside of the screen
  • Phosphors glow when struck by electrons
  • One each for red, green and blue
  • Stronger electron beam brighter color
  • If each red, green, and blue phosphor is struck
    equally, the result is a white dot
  • After the beam leaves a phosphor, it glows for a
    short time called persistence
  • For an image to remain stable, phosphors must be
    must be reactivated repeatedly by the electron

LCD Screens
  • Liquid Crystal Display
  • Named for the fact that there is a layer of
    liquid crystal material sandwiched in between the
    front and back panels that make up the LCD panel
  • Light emanating from a panel at the back of the
    screen spreads out in waves that vibrate in all

LCD Screens
  • The light emerging from each liquid crystal cell
    passes through one of three color filters red,
    blue, or green arranged very close to each
  • The colored beams of light pass through a second
    polarizing filter that only passes waves that are
    vibrating more or less vertically
  • Light that passed through a liquid crystal with a
    full charge is now oriented perfectly to pass
    through the second filter

LCD Screens
  • Since the filter is not precise, some of the
    light waves pass through that were only partially
  • Those without a charge are blocked completely
  • Since there are millions of combinations of
    charged cells producing millions of combinations
    of twisted molecules, the color on the screen is
    able to represent millions of colors to our eyes

Digital Light Processing DLP
  • DLP produces brighter, sharper images over a
    conventional projection system
  • By shinning a light through a spinning wheel
    divided into red, blue and green sections, each
    color is produced 60 times a second
  • After passing through the spinning disc, the
    light strikes a panel of 508,800 microscopic
    mirrors on the surface of a DLP chip
  • The mirrors reflect the light through a lens and
    onto a screen

Part 5 Major Concepts
  • Chapters 20-21
  • Mice
  • Mechanical
  • Optical
  • Touchpads and pointing devices

The Mechanical Mouse
  • Each roller is attached to an electronic wheel
  • A plastic wheel with tiny metal contact points
    that conduct electricity on it
  • Known as an Encoder
  • As the rollers turn, they rotate the encoders
  • Each encoder makes contact with a pair of
    electrical bars that pick up the signals made by
    the contacts as they spin past the bars
  • Each contact results in the generation of an
    electrical signal

The Mechanical Mouse
  • The number of signals indicates how many points
    the contact bars have touched
  • The greater the number of signals, the farther
    the mouse is moved
  • The more frequent the number of signals, the
    faster you are moving the mouse
  • Mouse direction
  • the ratio between the number of vertical signals
    to horizontal signals indicates the direction of
    the cursor travel on the screen

The Mechanical Mouse
  • Tapping either of the buttons on the mouse sends
    a signal to the PC which
  • results in an interrupt and tells the CPU to
    divert its attention to the command represented
    by the mouse click
  • Based on the location of the cursor when you
    click it
  • Based on the number of clicks you send via the

The Optical Mouse
  • Uses a small light projected onto the surface
    that the mouse travels over
  • A digital camera takes extreme close up pictures
  • Different shapes, ripples, pits, bumps and
    brightness differences in the surface the mouse
    travels over
  • Takes 1500 pictures a second
  • Digital signal processor analyzes each picture to
    calculate the speed and direction of the mouse

  • A layered pad consisting of a sandwich of
  • Rubber
  • Electrodes aligned vertically
  • Electrodes aligned horizontally
  • Positive and negative charges build up on each
    layer independently
  • Creates an electrical field between the layers
  • Integrated circuits for each layer vertical and
    horizontal sample the strength of each fields
    electrical potential or mutual capacitance

  • Capacitances are most affected by the center of
    the finger
  • By reading the capacitances of adjoining
    intersections, the touchpad can identify the
    fingers center
  • Location is fed to Windows to position the cursor
    or arrow
  • Capacitances measured about 100 times per second

Pointing Sticks
  • Resistors made of two electrical contacts
    separated by a film that resists the flow of
  • When pressure is exerted in a certain direction
    the contacts are pushed closer together
  • Creates a better connection between the 2
  • The closer the contacts become, the better the
    connection between the plates, the more
    electricity flows between the contacts
  • A circuit monitors the amounts of electricity
    flowing between the plates and translates this
    information into cursor speed and direction

Part 5 Major Concepts
  • Chapters 22-25
  • Modems and communications
  • Biometrics in computers
  • Fingerprints
  • Speech and voice recognition

Carrier Signal
  • Modem? Modulator/Demodulator
  • Modulation is applying information signal to the
    carrier signal
  • This example is frequency modulation, which is
    described in your text
  • Input/output device that enables your computer to
    communicate with a network

Modulated Signal
Analog (Information) Signal
Modem Info
  • Modems are used to convert digital computer
    information into a form the analog network can
  • Phone networks were built to support the human
  • Modems have several variationssome proprietary,
    some not really even modems
  • DSL/Cable are Terminal Adapters which speak
    only digital, but still provide the interface
    between the computer and the network

Slide 15