Review

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Review
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Secondary Memory Devices
Information is moved between main memory and
secondary memory as needed
Secondary memory devices provide long-term storage
Central Processing Unit
Hard disks Floppy disks ZIP disks Writable
CDs Writable DVDs Tapes
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A Computer Specification

• Consider the following specification for a
  personal computer
• 2.8 GHz Pentium 4 Processor
• 512 MB RAM
• 80 GB Hard Disk
• 48x CD-RW / DVD-ROM Combo Drive
• 17 Video Display with 1280 x 1024 resolution
• 56 Kb/s Modem
• What does it all mean?

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Software Categories

• Operating System
• controls all machine activities
• provides the user interface to the computer
• manages resources such as the CPU and memory
• Windows XP, Unix, Linux, Mac OS
• Application program
• generic term for any other kind of software
• word processors, missile control systems, games
• Most operating systems and application programs
  have a graphical user interface (GUI)

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Memory
Remember this?
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Storage Capacity

• Every memory device has a storage capacity,
  indicating the number of bytes it can hold
• Capacities are expressed in various units

Unit Symbol Number of Bytes
KB 210 1024
kilobyte megabyte gigabyte terabyte
MB 220 (over 1 million)
GB 230 (over 1 billion)
TB 240 (over 1 trillion)
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Bit Combinations

• Each combination can represent a particular item
• There are 2N combinations of N bits
• Therefore, N bits are needed to represent 2N
  unique items

21 2 items
22 4 items
23 8 items
24 16 items
25 32 items
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The Central Processing Unit (CPU)

• A CPU is on a chip called a microprocessor
• It continuously follows the fetch-decode-execute
  cycle

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The Central Processing Unit

• The CPU contains

Performs calculations and makes decisions
Arithmetic / Logic Unit
Coordinates processing steps
Control Unit
Small storage areas
Registers
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The Internet Then and Now

• The Internet was created by the Advanced Research
  Projects Agency (ARPA) and the U.S. Department of
  Defense for scientific and military
  communications.
• The Internet is a network of interconnected
  networks. Even if part of its infrastructure was
  destroyed, data could flow through the remaining
  networks.
• The Internet uses high-speed data lines, called
  backbones, to carry data. Smaller networks
  connect to the backbone, enabling any user on any
  network to exchange data with any other user.
• ARPANET, NSFnet, Internet
• Internetworking the process of connecting
  separate networks

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How the Internet Works - TCP/IP

• Every computer and network on the Internet uses
  the same protocols (rules and procedures) to
  control timing and data format.
• The protocol used by the Internet is the
  Transmission Control Protocol/Internet Protocol,
  or TCP/IP.
• No matter what type of computer system you
  connect to the Internet, if it uses TCP/IP, it
  can exchange data with any other type of
  computer.

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How the Internet Works - Routing Traffic Across
the Internet

• Most computers don't connect directly to the
  Internet. Instead, they connect to a smaller
  network that is connected to the Internet
  backbone.
• The Internet includes thousands of host computers
  (servers), which provide data and services as
  requested by client systems.
• When you use the Internet, your PC (a client)
  requests data from a host system. The request
  and data are broken into packets and travel
  across multiple networks before being
  reassembled at their destination.

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How the Internet Works - Addressing Schemes

• In order to communicate across the Internet, a
  computer must have a unique address.
• Every computer on the Internet has a unique
  numeric identifier, called an Internet Protocol
  (IP) address.
• Each IP address has four parts each part a
  number between 0 and 255. An IP address might
  look like this 205.46.117.104.

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Protocol LayerComments
Application Protocols LayerProtocols specific to applications such as WWW, e-mail, FTP, etc.
Transmission Control Protocol Layer TCP directs packets to a specific application on a computer using a port number.
Internet Protocol Layer IP directs packets to a specific computer using an IP address.
Hardware Layer Converts binary packet data to network signals and back.(E.g. ethernet network card, modem for phone lines, etc.)
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How the Internet Works - Domains and Subdomains

• In addition to an IP address, most Internet
  hosts or servers have a Domain Name System (DNS)
  address, which uses words.
• A domain name identifies the type of institution
  that owns the computer. An Internet server
  owned by IBM might have the domain name ibm.com.
• Some enterprises have multiple servers, and
  identify them with subdomains, such as
  products.ibm.com.

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Major Features of the Internet - The World Wide
Web

• The World Wide Web is a part of the Internet,
  which supports hypertext documents, allowing
  users to view and navigate different types of
  data.
• A Web page is a document encoded with hypertext
  markup language (HTML) tags.
• HTML allows designers to link content together
  via hyperlinks.
• Every Web page has an address, a Uniform Resource
  Locator (URL).

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Major Features of the Internet - File Transfer
Protocol (FTP)

• File transfer protocol (FTP) is the Internet tool
  used to copy files from one computer to another.
• Using a special FTP program or a Web browser, you
  can log into an FTP host computer over the
  Internet and copy files onto your computer.
• FTP is handy for finding and copying software
  files, articles, and other types of data.
  Universities and software companies use FTP
  servers to provide visitors with access to data.
  

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Major Features of the Internet - Telnet

• Telnet is a specialized service that lets you use
  one computer to access the contents of another
  computer a Telnet host.
• A Telnet program creates a "window" into the host
  so you can access files, issue commands, and
  exchange data.
• Telnet is widely used by libraries, to allow
  visitors to look up information, find articles,
  and so on.

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What Firewall Software Does

• A firewall is simply a program or hardware device
  that filters the information coming through the
  Internet connection into your private network or c
  omputer system. If an incoming packet of
  information is flagged by the filters, it is not
  allowed through.

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How Firewalls Work

• Firewalls use one or more of three methods to
  control traffic flowing in and out of the
  network
• Packet filtering - Packets (small chunks of data)
  are analyzed against a set of filters. Packets
  that make it through the filters are sent to the
  requesting system and all others are discarded.
• Proxy service - Information from the Internet is
  retrieved by the firewall and then sent to the
  requesting system and vice versa.
• Stateful inspection - A newer method that doesn't
  examine the contents of each packet but instead
  compares certain key parts of the packet to a
  database of trusted information. Information
  traveling from inside the firewall to the outside
  is monitored for specific defining
  characteristics, then incoming information is
  compared to these characteristics. If the
  comparison yields a reasonable match, the
  information is allowed through. Otherwise it is
  discarded.

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Firewall filters

• Firewall Configuration Firewalls are
  customizable. This means that you can add or
  remove filters based on several conditions. Some
  of these are
• IP addresses - A typical IP address looks like
  this 216.27.61.137. For example, if a certain IP
  address outside the company is reading too many
  files from a server, the firewall can block all
  traffic to or from that IP address.
• Domain names -. A company might block all access
  to certain domain names, or allow access only to
  specific domain names.
• Protocols - The protocol is the pre-defined way
  that someone who wants to use a service talks
  with that service. The http in the Web's
  protocol. Some common protocols that you can set
  firewall filters for include (next slide)
• Ports - Any server machine makes its services
  available to the Internet using numberedports,
  one for each service that is available on the
  server. For example, if a server machine is
  running a Web (HTTP) server and an FTP server,
  the Web server would typically be available on
  port 80, and the FTP server would be available on
  port 21. A company might block port 21 access on
  all machines but one inside the company.
• Specific words and phrases - This can be
  anything. The firewall will sniff (search
  through) each packet of information for an exact
  match of the text listed in the filter.

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Types And Sources Of Network Threats

• Denial-of-Service
• Unauthorized Access
• Confidentiality Breaches
• Destructive Behavior

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Acronyms you need to know

• IP (Internet Protocol) - the main delivery system
  for information over the Internet
• TCP (Transmission Control Protocol) - used to
  break apart and rebuild information that travels
  over the Internet
• HTTP (Hyper Text Transfer Protocol) - used for
  Web pages
• FTP (File Transfer Protocol) - used to download
  and upload files
• HTML (Hypertext Markup Language) - used to send
  text-based information (e-mail)
• URL (Uniform Resource Locator)- an address that
  identifies a particular file on the Internet,
  usually consisting of the protocol, as http,
  followed by the domain name.

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Acronyms you need to know

• GUI-
• RAM-
• ROM
• DVD
• CD
• CPU
• ALU
• OS-
• I/O-

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Acronyms you need to know

• GUI- Graphic User Interface
• RAM-Random Access Memory
• ROM- Read Only Memory
• DVD- Digital Versatile Disk
• CD- Compact Disc
• CPU- Central Processing Unit
• ALU- Arithmetic Logic Unit
• OS- Operating System
• I/O- Input/Output