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The Computer System


A computer is an electronic device, operating under the control of instructions ... virtually any type of video device, such as VCRs, televisions, and camcorders. ... – PowerPoint PPT presentation

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Title: The Computer System

The Computer System
What is a Computer?
  • A computer is an electronic device, operating
    under the control of instructions stored in its
    own memory unit, that can accept data (input),
    process data arithmetically and logically,
    produce results (output), and store the results
    for future use.

Components of a computer
  • Basic Components
  • Input Devices
  • System Unit
  • Output Devices
  • Storage Devices
  • Other Components
  • Peripheral Devices
  • Communication Devices

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Strengths of Computers
  • Speed
  • Reliability
  • Accuracy
  • Storage
  • Communication/Connectivity

Types of Computer
  • Microcomputer (PC)
  • Workstation
  • Minicomputer
  • Mainframe Computer
  • Supercomputer

Increasing speed processing power!
Data Representation
  • Bits
  • off or on digital value, short term for binary
  • Bytes
  • a group of eight bits, a unique code can be
    assigned to 256 different data possibilities.
    (e.g. 01000001 represents the letter A.)

Coding Scheme
  • ASCII (American Standard Code for Information
  • 8 bits used in many PC minicomputer.
  • EBCDIC (Extended Binary Coded Decimal Interchange
  • 8 bits used in Mainframe Computer
  • Unicode
  • 16 bits
  • can represent gt 65000 characters

1. System Unit
Components of System Unit
  • Motherboard
  • Central Processing Unit (CPU)
  • Memory
  • Upgrade sockets
  • Co-processor
  • Buses
  • Expansion Slot
  • Ports connectors

The Central Processing Unit
  • It is the brain of a computer system
  • The CPU
  • receives input.
  • interprets instructions provided by programs.
  • directs other components of the system to act.
  • processes data.
  • controls output.

The Central Processing Unit
  • Control Unit
  • It coordinates the flow of data and instructions.
    It contains a clock that generates a uniform
    stream of electrical pulses that synchronize the
    operating of the CPU and other computer components

Note The control unit controls the computer by
repeating 4 operations, called the machine cycle.
The 4 operations are fetching program
instructions from memory decoding the
instructions into commands that the computer can
process executing the commands and storing the
results in memory
The Central Processing Unit
  • Arithmetic and Logic Unit (ALU)
  • It performs calculations and comparisons of data.

The Central Processing Unit
  • Registers
  • They hold program instructions, data values, and
    memory locations as the computer executes a

The Central Processing Unit
Buses They are electrical pathways that carry
signal (bits) between a CPUs components and
outside devices.
  • Large computer systems, as well as newer
    workstations and network servers, frequently
    contain more than one central processing unit.
  • Multiple CPUs enable the computer to execute more
    than one instruction or process more than one
    program, at the same time.

Main Memory
  • Before programs are executed or data processed,
    they must first enter into main memory.
  • Main memory holds information read from disk or
    captured by input devices.
  • The CPU then moves information from the main
    memory into its registers for processing.

Random Access Memory (RAM)
  • Integrated circuit containing data that can be
    read and written by the microprocessor or other
  • Volatile - programs data stored in RAM are
    erased when the power is off.

Read Only Memory (ROM)
  • Chips that store information or instructions that
    can be read and used, but cannot be changed.
  • Non-volatile - retains its contents even the
    power is turned off.
  • The instructions to start the computer are on a
    special chip known as a ROM BIOS chip (Basic
    Input/Output System).

Cache Memory
  • Cache memory is a specialized chip used with the
    computer's memory.
  • Cache chips are faster and more expensive than
    regular RAM chips.
  • The computer stores the most frequently used
    instructions and data in cache. Cache has a
    relatively small storage capacity but can
    significantly increase the system's speed.

In summary, memory
  • accepts and holds program instruction and data
  • acts as the CPUs source for data and
    instructions and as a destination for operation
  • holds the final processed information until it
    can be sent to the desired output or storage
    devices, such as printer or disk drive

  • A circuit board that contains most of the
    electronic components of the system unit.

CPU Slot (PII)
DIMM Sockets for Memory
Internet References How microprocessor works
) Introduction to PC (http//
/index.htm) Computer Hardware (http//
hk/has/comp/component/index.htm) Toms Hardware
Guide (http//
) Multimedia Tutorials (Available in SLCSS
Intranet Only) Lab 1 Computer Fundamentals Lab
2 Central Processing Unit
2. Input Devices
Input Devices
  • Input devices, such as keyboards or scanners, are
    hardware components that capture, collect, and
    transmit data and programs to the computer in a
    form that computer can understand.
  • Input devices transmit the input to the computer
    in a series of electronic pulses representing
    bits, or digits, of the binary code.

Types of Input
  • Data
  • raw facts that a computer receives and processes
    to produce information
  • Programs
  • instructions that direct the computer operations
  • Commands
  • key words that direct the computer to perform
    certain activities
  • User Responses
  • data a user enters to respond to a question or

A. Keyboard
  • The most commonly used input devices.
  • Contains alphanumeric, cursors and function keys.

  • Function Keys, labeled from F1 to F12, allow user
    to quickly access commands and functions, such as
    saving a document or calling up a programs Help
  • Cursor-control Keys govern the movement of the
    cursor on the screen. They include Up Arrow, Down
    Arrow, Left Arrow and Right Arrow key on the
  • Special Purpose Keys are used in conjunction with
    other keys to enter commands into a computer.
    Control (Ctrl), Alternate (Alt) and Shift keys
    are example of special purpose keys.

  • Toggle Keys are keys that, when pressed,
    activates a certain mode or condition, and when
    pressed again, deactivates the condition. The Num
    Lock key, Cap Lock key and the Scroll Lock key
    are examples of toggle keys. (For example,
    pressing the Cap Lock key will cause all the
    alphanumeric characters to appear in capitals
    without holding down the Shift key.)
  • Numeric Keypad, located in the far right portion
    of the keyboard, is used for entering numbers
    quickly and for performing the same operations as
    a calculator.

Not all keyboards have the same layout. Most
keyboards have adopted the so-called QWERTY
layout for the alphanumeric keys.
Types of Keyboard
B. Pointing Devices
  • Many people use pointing devices instead of
    keyboards whenever possible.
  • Pointing devices minimize the amount of typing
    (and the number of errors).

  • Palm-sized pointing devices
  • a ball on the bottom senses its movement
  • various actions can be preformed by moving the
    pointer and then pressing one of the buttons on
    top of the mouse.

Types of Mouse
Mouse Interfaces
  • Up-side down mouse
  • user rotates the ball itself while clicking
    nearby buttons

The mouse is not practical for people using a
notebook computer in a small space. Track Point
or Touch pad is therefore used instead to control
the pointer.
Touch-Sensitive Screens
  • Touch screens enable the user to select an option
    by pressing a specific part of the screen.
  • Touch screens are commonly used in grocery
    stores, fast-food restaurants, and information

  • Use the movement of a vertical stem to direct the

C. Pen Input Devices
  • Input data with hand written characters, select
    items by pressing the pen against the screen, and
    use gestures, which are special symbols, to issue

Light Pen
  • Used to select processing options or to draw on
    the screen

The tip of a light pen contains a highly
sensitive photoelectric cell. When the light pen
is pointed close to the screen, the photoelectric
cell detects the light emitted from the exact
spot the pen is touching. This accuracy makes
light pens very popular among engineers and
draftsmen who use computer-aided design (CAD)
software to create blueprints and drawings of
products or construction projects.
Digitizing Tablet
  • A digitizing tablet consists of a grid on which
    designs and drawings can be entered.
  • Most tablets are pressure-sensitive, and the
    user draws directly on the tablet using a special
    pen called a stylus.
  • Digitizing tablets are used to design cars,
    buildings, medical devices, and robots.

Chinese Handwriting Recognition Device
  • Used for inputting and recognizing Chinese

Nowadays, sophisticated Chinese handwriting
recognition system also contains voice
recognition function.
D. Scanning Devices
Image Scanner
  • Electronically capture an entire image convert
    it into digital form that can be processed by a

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Bar Code Reader
  • Bar code consists of a set of vertical lines and
    spaces of different widths
  • Universal Product Code (UPC) is very common

Magnetic Ink Character Recognition (MICR)
  • Use a special ink that can be magnetized during
  • MICR is used by the banking industry as a means
    of processing checks it receives in every day.

Optical Character Recognition
  • a system of producing machine-readable code on a
    data source item and reading that code by means
    of optical scanning devices.
  • OCR software can be installed in a computer to
    perform character recognition.

Optical Mark Recognition
  • Optical marks are the filled-in shape, usually
    ovals or rectangles, on scan sheets.
  • The data collected on the scan sheets are
    translated into binary form by an optical mark
    reader (OMR)

Use lead pencil to mark on scan sheet
Feed the scan sheets into the OMR
Smart Card
  • A smart card, often the size of a credit card,
    contains a built-in microprocessor and memory
    that identify the card (and its owner) and
    assists in financial and other transactions.
  • Its primary advantage is increased security the
    information can only be read by an authorized
    user with appropriated password.

E. Multimedia Input Devices
Voice Input Devices
  • A voice input device has two functions
  • First, it can simply record and play back the
    voice inputted by the user.
  • Secondly, it can record a human voice, then with
    appropriate voice recognition software, convert
    the voice input to ASCII characters.

Digital Camera
  • Record images in a form that can be stored by a
  • Some digital cameras resemble traditional cameras
    and are portable. Some are connected directly to
    a computer.

Video digitizers
  • Video digitizers can capture input from virtually
    any type of video device, such as VCRs,
    televisions, and camcorders.
  • Audio digitizers can digitize music or voice from
    a microphone.

Internet References Jans Illustrated Computer
Literacy 101 (http//
sonintro.htm) Introduction to PC
(http// Computer
Hardware (http//
index.htm) Toms Hardware Guide
(http// Mul
timedia Tutorials (Available in SLCSS Intranet
Only) Lab 3 Input/Output Devices
Storage Devices
Storage Devices
  • Also called secondary storage
  • store data programs permanently for future use
  • can be used as both input output devices

Magnetic Disk Storage
  • Most widely used storage medium
  • consists of a round piece of plastic or metal,
    the surface on which is covered by a magnetic
  • e.g. floppy disks, hard disks and removable disk

Floppy Disk
  • Random-access storage medium
  • provides storage of 1.44MB data
  • A circular piece of thin plastic that is coated
    with magnetic material
  • the circular piece of plastic is enclosed by a
    rigid plastic shell
  • Formatting prepares a floppy disk for storage by
    defining the tracks, cylinders, and sectors on
    the disk surface
  • time required to locate data and transfer it to
    memory is called the access time.

Data is recorded on disk in concentric circular
bands called tracks. The tracks on a disk are
similar to the grooves on a phonograph record.
Each track is divided into pie-shaped wedges
called sectors. Two or more sectors combine to
form a cluster.
Most computers maintain on the disk a table with
the sector and track locations of data. This
table, the file allocation table (FAT), enables
the computer to locate data easily.
Structure of a Floppy Disk
Hard Disks
  • Fixed in the System Unit
  • Consists of one or more rigid platters coated
    with a magnetic material
  • the platters, read/write heads, and the access
    arms that move the heads across the disk surface
    are all enclosed in an airtight, sealed case

  • Access time for a hard disk is significantly less
    than that for a floppy disk because a hard disk
    spins faster and unlike a floppy disk, a hard
    disk is spinning constantly (7200 revolutions per
  • hard disks are permanently encased within the
    disk drive in a sealed environment free from dust
    and dirt. The disk can spin very rapidly, with
    the read/write head "floating" above the disk's

Hard Disk Interfaces
  • To connect a hard disk to a microcomputer
    motherboard, you must have a hard disk interface.
  • This component includes circuitry that conforms
    to a standard recognized by both the hard disk
    and the motherboard manufacturer.
  • Common standards are Integrated Drive Electronics
    (IDE) and Small Computer System Interface (SCSI).

Removable Disks
  • Provide both the storage capacity and fact access
    time of hard disk and the probability of floppy
  • Examples
  • Iomegas ZIP (100, 250, 750 MB)
  • Imations Superdisk (120MB)
  • Sonys MO Disk (49GB)

Maintaining Stored Data
  • To prevent loss of data, 2 procedures should be
    performed regularly
  • Backup
  • process of creating a copy of important programs
    and data
  • Defragmentation
  • process of reorganizing data stored on a disk so
    that files are located in contiguous (adjacent)

CD-ROM and Optical Disks
  • By using laser technology, optical disk can store
    large quantities of data
  • a high power laser writes data on an optical disk
    by burning microscopic holes on the disk surface
  • a lower power laser reads the data by reflecting
    light off the disk surface. The reflected light
    is converted into a series of bits

  • CD-ROM
  • CD-Read Only Memory
  • can store 650 MB data
  • suitable for reference material such as
    encyclopedias, catalogs and pictures
  • CD-R
  • CD-Recordable
  • write once, read many
  • CD-RW
  • CD-Rewritable
  • erasable write many, read many
  • MO
  • Magneto-Optical
  • Floptical (Optical Magnetic)

Magnetic Tape
  • Consists of a thin ribbon of plastic, one side of
    which is coated with a material that can be
    magnetized to record binary data.
  • A sequential storage media (must write and read
    records on after another)
  • usually cartridge tape
  • serves as a primary means of
  • backup,
  • a method of transferring data between system, and
  • a cost-effective way to store data that does not
    have to be accessed immediately

Other types of Storage Devices
  • PC Cards (PCMCIA)
  • Compact Flash Memory Card
  • Memory Stick
  • Smart Card

Output Devices
Types of Output
  • Output is data that has been processed into a
    useful form called information.
  • Report
  • Computer Graphics
  • Audio Output
  • Video Output

Types of Output
  • Most output can be divided into 2 categories
    Soft copy hard copy.
  • Soft copy is what you see on the monitor. Soft
    copy is temporary.
  • Hard copy can be touched and carried. Hard copy
    is usually some form of paper output.

  • A visual output device of a computer.
  • Monitor output is a most common form of soft copy.

CRT Monitor
Flat-panel Monitor
Resolution of Display
  • Images on the screen are created by
    configurations of dots called pixels (picture
  • The more the pixels, the better the resolution of
    the image
  • SVGA pixel configuration of 800 by 600
  • XVGA pixel configuration of 1024 by 768

  • Produce permanent output (hard copy)
  • consists of 2 main types impact non-impact

Impact Printers
  • Line printers
  • they can produce only text--no graphics.
  • Chain printers
  • Dot Matrix Printers
  • The most common character printers create images
    by using a dot pattern.

Non-impact Printers
  • Laser Printer
  • work in the same manner as copy machines a laser
    beam creates electrical charges that attract
    toner to form an image and transfer it to paper.

Color Laser Printer
Laser Printer
  • Inkjet Printers
  • significantly less expensive than laser printers
  • relatively low resolution
  • Electronically charged ink is sprayed through a
    jet nozzle and passed through an electronic
    field, which deflects the ink to form a
    dot-matrix character

Other Output Devices
  • Plotter
  • produce high-quality line drawings
  • A continuous-curve plotter is used to draw maps
    from stored data.

  • LCD Projectors
  • project a computer image onto screen
  • Voice Output Devices
  • generate spoken words from text
  • Computer Output microfilm (COM)
  • records output as microscopic images on roll
  • Facsimile (FAX) Machine
  • transmit receives document over telephone line.
  • Multifunctional Devices (MFD)
  • can print, copy and fax