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Data Communications and Computer Networks


The computer itself can take care of the processing function, but it needs ... Computer hardware is useless without software. Software is the set of ... – PowerPoint PPT presentation

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Title: Data Communications and Computer Networks

Data Communications and Computer Networks
  • CIS 454/554
  • Instructor Sanchita Mal-Sarkar

  • An electronic machine that accepts input,
    processes data, stores data, and produces output.
  • Data can be numbers, text, images, graphics, and
    sound, etc.
  • Computer program is a set of instructions.
    Without it computer is useless.
  • Programming languages allow us to write these
    instructions (e.g. C, C, Java, etc).

Computer system
  • A computer system consists of a computer,
    peripheral devices, and software.
  • The computer itself can take care of the
    processing function, but it needs additional
    components, called peripherals, to accomplish its
    input, output and storage functions.
  • Example of an internal peripheral device is hard
    disk drive.

Computer Hardware
  • Hardware is the physical component of a computer.
  • Hardware is the equipment used to perform the
    necessary computations.
  • Examples
  • Main memory (RAM, ROM), secondary memory (hard
    disk drive, floppy disk drive), CPU, input
    devices (keyboard and mouse), and output devices
    (monitor and printer).

Hardware Components of a Computer System
  • Central Processing Unit (CPU)
  • Arithmetic-Logic Unit
  • Control Unit

Input Devices
Secondary Storage
  • Magnetic disk
  • Optical disk
  • Magnetic tape
  • Keyboard
  • Computer mouse
  • Touch screen
  • Source data automation

Output Devices
  • Printers
  • Video display terminals
  • Plotters
  • Audio output

Communications Devices
Primary Storage
Central Processing Unit (CPU)
  • Coordinating all computer operations.
  • Performs arithmetic and logical operations on
  • To process a program stored in main memory,
  • - CPU retrieves each instruction in
  • - Interprets the instruction to determine
    what should be done.
  • - Retrieves any data needed to carry out
    that instruction
  • - Then CPU performs the actual
  • CPUs current instruction and data values are
    stored temporarily inside the CPU in special
    high-speed memory locations called registers.

Central Processing Unit (CPU)
  • The CPU consists of a control unit and an
    arithmetic-logic unit.
  • Three kind of buses link the CPU, primary
    storage, and other devices in the computer
  • The data bus moves data to and from primary
  • The address bus transmits signals for locating a
    given address in primary storage.
  • The control bus transmits signals specifying
    whether to read or write data to or from a given
    primary storage address, input device, or output

Data Bus, Address Bus, and Control Bus
Central Processing Unit (CPU)
Arithmetic-Logic Unit 24 12 36
12 lt 24
Control Unit
Data Bus
Address Bus
Control Bus
Output Devices
Secondary Storage
Input Devices
Computer Software
  • Software consists of the computer programs that
    allow us to solve problems by providing sets of
  • Examples
  • DOS, Windows, Mac. Office family, Lotus,
    Netscape, Internet Explorer, Virus scans, tax
    programs, computer games, GUI - Graphical User

Computer Software
  • Computer hardware is useless without software.
  • Software is the set of instructions and
    associated data that direct the computer to do a
  • Software can be divided into two categories
  • system software and application software.
  • System software helps the computer to carry out
    its basic operating tasks.
  • Application software helps the user carry out a
    variety of tasks.

The major types of software
System Software Operating
Systems Schedules computer events Allocates
computer resources Monitor events
Application software
System software
Language translators Interpreters
Application Software Programming
languages Assembly language FORTRAN, BASIC,
PL/1 PASCAL, C 4th generation languages
Utility programs Routine operations (e.g.
sort, list,
print) Manage data (e.g. create files,
merge files
System Software
  • Manages the fundamental operations of the
    computer, such as
  • loading programs and data into memory, executing
    programs, saving data to disks, displaying
    information on the monitor, and transmitting data
    through a port to a peripheral device.
  • Four types of system software operating systems,
    utilities, device drivers, and programming

Operating System
  • Collection of computer programs that control the
    interaction of the user and the computer
  • Responsible for directing all computer operations
    and managing all computer resources.
  • Controls basic input and output, allocates system
    resources, manages storage space, maintains
    security, and detects equipment failure.
  • A part of the operating system code is stored in
    a ROM and the rest of it resides on a disk.
  • Loading the operating system into memory is
    called booting the computer.

Responsibilities of an Operating System
  • Communicate with user, receive and execute
    commands, show error messages.
  • Manage allocation of memory, processor time and
    other resources.
  • Collect input from keyboard, mouse, and provide
    data to running programs.
  • Convey program output to screen, printer, or
    other output device.
  • Access data from secondary storage.
  • Write data to secondary storage.

Application software
  • Developed for a specific task , such as word
    processing( MS Word/ WordPerfect), accounting
    (Lotus 1-2-3/ Excel), or database management
    (Access/ dBASE).
  • Most applications are purchased on diskette or
  • They are installed by copying the programs from
    the diskettes/CD-ROM to the hard disk.

Data Communications
  • The transmission of text, numeric, voice, or
    video data from one machine to another is called
    data communications.
  • For example, Send an electronic mail to your
    friends around the globe.
  • The four essential components of data
    communications are a sender, a receiver, a
    channel, and a protocol.
  • Sender gt The computer that originates the
    message is called the sender.
  • Receiver gt The computer at the messages
    destination is called the receiver.

Data Communications
  • Channel gt The message needs some kind of medium
    to be transmitted. This medium is called channel.
    For example, telephone or coaxial cable,
    microwave signal, or optical fibers
  • Protocol gt The rules that establish an orderly
    transfer of data between the sender and the
    receiver are called protocols.
  • Computer software and hardware establish these
    protocols at the beginning of the transmission,
    and both computers have to follow the protocols
    to ensure accurate transfer of data.

  • One of the most important types of data
    communications in the business world is a network
  • A network connects one computer to another
    computers and peripheral devices to share data
    and resources.
  • There is a number of network configurations.
  • local area network (LAN) gt computers and
    peripheral devices are located relatively close
    to each other, generally in the same building.
  • Client/server networks gtSome networks have file
    servers (one or more computers) that act as the
    central storage location for programs and that
    provide mass storage for most of the data used on
    the network. A network with a file server is
    called a client/server networks.

  • Peer-to-peer networks gt When a network does not
    have a file server, all the computers essentially
    are equal, and programs and data are distributed
    among them. This is called a peer-to-peer
  • Each computer that is part of the network must
    have a network interface card installed. This
    device creates a communication channel between
    the computer and the network.
  • Network software is also essential to establish
    the communications protocols.
  • Standalone computer gt A microcomputer that is
    not connected to a network is called a standalone

  • Allows us to send and receive data over telephone
  • A modem connects a computer to a telephone jack.
  • At the sending site, modem converts the digital
    signal from a computer into analog (continuous
    wave) signals (sound waves) that can traverse
    ordinary phone lines (modulation).
  • At the receiving site, a second modem converts
    the analog signals back into digital signals

  • The internet was originally developed for the
    government to connect the researchers around the
    world to share data.
  • Today, the internet is the largest network in the
    world that connects millions of people in almost
    200 countries.
  • The use of internet
  • electronic mail gt This is the capability to send
    a message from one users computer to another
    users computer where it is stored until the
    receiver opens it. Message passes through
    electronic links called gateways.
  • World Wide Web (Web) gt Web is a huge database of
    information that is stored on the network servers
    in places that allow public access. The
    information is stored as text files called web

  • Hyperlinks gt a place on a computer screen that
    is programmed to connect to a particular file on
    the same network server, or on a network server
    on the other side of the globe.
  • Web browsing gt communication software that help
    us navigate the WWW is called web browsing
    software or web browser.