IT 212 002
How Computers Work
May 3, 2007
Wireless LAN, Cell Phones,
Bluetooth
Final Review
GMU IT 212 - Spring 2007
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Lecture Agenda
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Chapter 26: How Wireless Sets PCs Free
Final Exam Review
GMU IT 212 - Spring 2007
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Chapter 26: How Wireless Sets
PCs Free
GMU IT 212 - Spring 2007
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Wireless LAN
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A wireless local area network (WLAN) is a LAN that
does not use wires as a connection medium
Ethernet example of LAN
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Wi-fi, also known as IEEE 802.11, is an example of a
WLAN
There are many versions of the IEEE 802.11
standard including:
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802.11b
802.11a
802.11g
802.11n (coming soon)
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Current Flavors of Wi-Fi
Standard
802.11b
802.11a
802.11g
Speed
11Mbps
54Mbps
54Mbps
Speed
100-150 feet 25-75 feet
100-150 feet
Frequency
2.4GHz
5GHz
2.4GHz
Low
High
Acceptance High
(compatible with
802.11b)
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Wireless Access Points/Routers
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For home use, typically have a wireless router or wireless access point (AP)
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Wireless router = Wireless access point plus a router
Wireless router allows you to share one DSL/cable modem connection among several wireless
computers
Wireless access point needs a separate router to share broadband connection
Wireless router connects directly to DSL/cable modem via Ethernet cable
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Also possesses a switch (4-port) which allow you to connect wired desktop computers to the
network
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Wireless Stations
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Wireless nodes on the
network are called stations
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A wireless network
adapter is used to connect
to the wireless LAN
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Laptops, PDAs, printers,
digital cameras, etc.
PC card adapter
USB adapter
PCI adapter (desktops)
Built-in adapter
Has unique MAC address
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Wireless Protocol
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Wireless station broadcasts probe
request
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If an AP is within that range, the AP
picks up the probe request and
broadcasts an acknowledgement
including its service set identifier
(SSID)
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Discovers which 802.11 APs in range
The two stations go through a process
that involves authentication
The AP and the station send packets to
each other using specific addresses
Extension points may be used to
extend the coverage of a wireless
network
Point-to-point (computer-to-computer)
networks are also possible for Wi-fi
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Securing your WLAN Access Point
The following measures can all be broken, but offer
a certain measure of security
Disable broadcast of SSID
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1.
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Node must ask “Is Bob there?” to get a response
Normally asks “Is anyone there?”
Apply MAC filtering
2.
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Limit which MAC addresses can access your network
Apply encryption with WEP (wired equivalent
privacy)
3.
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Use highest number of bits (128 bits)
Encrypts data traveling between station and access point
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Cell Phones
-1983 Motorola DynaTEC Cell phone
-Around 38 ounces (1.75 pounds)
-10 inches tall
-2007 Motorola Razr
-Around 3.3 ounces
-3.8 inches tall
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Cell Phone Operation
MTSO
Mobile Telephone
Switching Office
PSTN
Public Switched
Telephone Network
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Base station covers a certain area called a cell
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When a mobile user turns the cell phone on, the cell phone communicates with the base station over a
channel called the control channel
The cell phone listens to the System Identification Code (SIC) that is broadcast over the control
channel
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Each base station connected to a switching center called the Mobile Terminal Switching Office (MTSO)
MTSO connected to public switched telephone network
The SIC gives the cell phone information regarding the base station
The cell phone also sends a registration request over the control channel which is passed over to the
MTSO
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The MTSO contains subscriber info
The MTSO is also responsible for billing the user
Has the ability to assign which frequencies the mobile units may use to communicate with the base station
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Cell Phone Operation
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Neighboring base stations
use different
communication frequencies
to avoid garbled
communications
As phone moves from one
cell to another
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Mobile user
Base station
Signal grows weaker
Neighboring station
monitors strength on other
frequencies, not only its
own
When next station signal is
stronger than current
station, stations coordinate
to transfer call on new
frequency
Called a handoff
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Analog versus Digital
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Most cell phones today are digital but earlier
ones were analog
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Analog send analog signals to base station using
carrier radio waves
Digital cell phone digitize audio signals using ADC
circuits and radio wave carriers to send
information to base station
Analog phones higher power than digital
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FDMA vs TDMA vs CDMA
www.owlnet.rice.edu/~elec301/Projects01/cdma/compare.html
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Multiple access = method to share a resource over many users
FDMA = frequency division multiple access
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TDMA = time division multiple access
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Users are separated in frequency i.e. mobile phones communicate at different frequencies than the
others within each cell.
Analog phones
User are separate in time slots, can only communicate in allotted time slot
Used by GSM (Global System for Mobile Communication) phones
US Carriers: Cingular, T-Mobile
CDMA = code division multiple access
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Users simultaneously use all frequencies and time slots available, assigned codes which do not
interfere with one another
US Carriers: Verizon, Sprint
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GSM versus CDMA
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Most of the world uses GSM
 SIM (subscriber identity module) card contains user account
information, address book, etc.
 To use phone overseas…
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Phone must be unlocked (i.e. can use any SIM card)
Make sure frequencies compatible: quad-band phone
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US: 850 MHz,1900 MHz
Europe: 900 MHz, 1800 MHz
Next generation, moving to 3G (currently 2G or 2.5G) data
services
Three competitors, all based on CDMA
 CDMA2000: based on 2G CDMA
 WCDMA: Wide-band CDMA; new European standard
 TD-SCDMA: Time-division Synchronous Code-Division Multiple
Access, in China
3G networks have potential transfer speeds of up to 3 Mbps
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Bluetooth
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Bluetooth is a standard protocol for connecting wireless devices
to each other located within a close vicinity
 Harald Bluetooth is a Danish king who unified Scandinavia
 Bluetooth devices comprise a radio module that incorporates
the Bluetooth protocol
 The range is limited to about 30 feet and data rate to a maximum
of around 1Mbps
The link manager is a piece of software in the Bluetooth device
to set up communications with other devices and to send/receive
signals to/from them
Bluetooth devices may operate in a variety of modes including:
 Standby, Page, Inquiry, Park and Hold
Bluetooth security issues
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Bluetooth
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Uses Frequency Hopping
Spread Spectrum
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Radio transmissions between
devices “hop” between 79
different frequencies
Change frequencies 1,600
times per second
Hopping done to minimize
interference
Transmit at 1 mW
Killer app: Bluetooth
headsets
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Final Exam Review
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Final Exam
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Open book, open notes
True/false, multiple choice, short answer
Students required to bring scantron form
882-E and a number 2 pencil!!!
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Chapters from book to review
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How Computers Works, 8th Edition
This semester we covered:
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Chapters 1-19
Chapters 21-22
Chapters 24-27
You are responsible for textbook material for
topics covered in class
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Review of lecture topics
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Goals of the course
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Upon the successful completion of this course,
the student will be able to:
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Describe the basic components of today’s personal
computer and how they function together
Understand some of the historical developments that
have resulted in today’s personal computers
Understand the basic operation and function of today’s
personal computer
Understand what the Internet is and some of the
historical developments that resulted in its creation
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Jan 25—Introduction & Syllabus,
History
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Define computer
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A programmable machine that inputs, processes and
outputs data.
Any device capable of processing information to produce a
desired result. No matter how large or small they are,
computers typically perform their work in three well-defined
steps: (1) accepting input, (2) processing the input
according to predefined rules (programs), and (3)
producing output.
In general, a device that uses digital technology to process
and manipulate information.
An electronic device that stores, retrieves, and processes
data, and can be programmed with instructions. A
computer is composed of hardware and software, and can
exist in a variety of sizes and configurations.
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Four Functions of a Computer
A computer has four functions:
a. accepts data
b. processes data
c. produces output
d. stores results
Input
Processing
Output
Storage
The Information Processing
Cycle
Storage
Input
Processor
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Output
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History of computers
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In 1837, Charles Babbage designed a fully programmable mechanical computer that he
called "The Analytical Engine".
Large-scale automated data processing of punched cards was performed for the US
Census in 1890
A succession of steadily more powerful and flexible computing devices were constructed in
the 1930s and 1940s, adding key features seen in modern computers.
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The US Army's Ballistics Research Laboratory ENIAC (1946)
EDSAC: first computer to implement the stored program (von Neumann) architecture
(1952).
Vacuum tube-based computers were in use throughout the 1950s,
Replaced in the 1960s by transistor-based devices
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Creation of microprocessors such as the Intel 4004
By the 1980s, computers became sufficiently small and cheap to replace simple
mechanical controls in domestic appliances
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Smaller, faster, cheaper, less power and more reliable
By the 1970s, integrated circuit technology
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The use of digital electronics (largely invented by Claude Shannon in 1937), more flexible
programmability were vitally important steps
Computers became widely accessible for personal use by individuals
Home computers and personal computers.
Widespread growth of the Internet since the 1990s
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Feb 1—Hardware, Wake-up Process,
Boot-Up, Operating Systems
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Inside a PC case
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Motherboard (see textbook for contents)
Power supply
Hard Disk Drive
Media Drives: CD ROM, DVD ROM, Tape,
USB Flash, Floppy
IDE Controller: disk drives
AGP, PCI-E
Video Card
Sound Card
RAM
Clock
BIOS
Microprocessor (CPU)
Heat Sink and Fan
Buses
USB
Keyboard
Network Controller
Parallel Port
Serial Port
Modem
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Operating Systems
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An operating system (OS) is a computer program
that manages the hardware and software resources
of a computer. Performs basic tasks such as
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controlling and allocating memory
prioritizing system requests
controlling input and output devices
facilitating networking
managing files
May provide a graphical user interface for higher level
functions
It forms a platform for other software
Discussed Windows, Mac, Unix/Linux
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How a PC Wakes Up: 2 steps
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Power-On Self Test (textbook pp. 24-25)
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From turn on of power switch to transferring
control from BIOS to operating system (OS) on
hard disk
Disk Boot (textbook pp. 26-27)
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After POST, processor executes program
contained on hard drive’s boot sector for OS to
take control
Continues until Windows logon screen
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Hardware and Software Work
Together
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The operating system quickly evolved into an
all-encompassing bridge between your PC
and the software you run on it
Device driver
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A device driver is a specific type of computer
software, typically developed to allow interaction
with hardware devices.
EIDE—hard disk driver
Hardware interrupts
How Plug and Play Works
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Feb 8—Semiconductors, Transistors,
RAM, Microprocessors
Video Card
CPU
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North Bridge
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Hard Drive
Memory (RAM)
CPU
Video Card
Frontside Bus (FSB)
fast between RAM and
CPU
Backside Bus, not
shown, connects CPU
to L2 cache
South Bridge connects
other I/O such as disk
drives, sound cards,
Ethernet, etc.
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Plug and Play Rules
Devices on These Buses
or Connectors
Can Be Added to or
Removed from a Running
System?
USB, IEEE 1394, PC
Card devices, CardBus
devices
Yes. Remove hardware by No.
using the Safely Remove
Hardware application if it
appears in the notification
area.
PCI, ISA, EISA
No.
Yes.
Docking station
Varies among computer
manufacturers; most
support docking and
undocking while the
computer is running.
Varies among computer
manufacturers; most
support docking and
undocking while the
computer is running.
GMU IT 212 - Spring 2007
System Must be Turned
Off Before Device is
Added to or Removed
from System?
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Windows Registry
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Every operating system and application needs a place to store
configuration settings and user preferences
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Windows originally used INI files
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MS-DOS uses CONFIG.SYS
DOS programs made own arrangements for user settings
Read and written using special routines
Windows had one configuration file, SYSTEM.INI, used for all the internal
settings
Plus another, WIN.INI, for user preferences
Each application had an INI file
INI files were slow to access and limited to 64Kb
Unsuited for the 32-bit versions of Windows
So for Windows NT and Windows 95 Microsoft introduced the Registry
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A database for storing and accessing configuration data
Organized for fast and efficient access
Data is stored in a hierarchical manner like the folders on a hard disk
Registry data that is currently in use is cached to provide better performance
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Binary Arithmetic, Transistors
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The simplest arithmetic operation in binary is addition. Adding
two single-digit binary numbers is relatively simple:
 0+0=0
 0+1=1
 1+0=1
 1 + 1 = 10 (carry:1)
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Multiple bits
 1 1 1 1 1 (carry)
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01101
 +10111
 ------------ 100100
A transistor is the basis of integrated circuits, works as a switch
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Feb 15—Programming Languages, How
Windows Works, How Applications Work
 PC computer memory is divided into
segments,
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64 kilobytes each (65,536 bytes, to be exact)
Segment register in microprocessor indicates
segment is to be accessed
Segment 0
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Contains memory pointers, device drivers,
buffers, input/output ports, and other essential
information required by the computer and its
operating system
Segment 0 contains 65,536 memory addresses
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Memory Map of Segment 0
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Mar 1, Mar 22—Long Term Memory,
Disk Drives, Optical Storage
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Volatile vs Non-Volatile memory
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Magnetic Storage/Hard drives
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Volatile memory does not retain its information
without constant power
Non-Volatile maintains information indefinitely
Chapters 9-11 in textbook
Optical drives
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Chapter 12 in textbook
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Magnetic Storage
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Media used in removable magnetic-storage devices is coated with iron
oxide
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The media is typically called a disk or a cartridge
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Each head has a tiny electromagnet (an iron core wrapped with wire)
The electromagnet applies a magnetic flux to the oxide on the media
The oxide permanently "remembers" the flux last saw
During writing, data signal sent through a coil to create a magnetic field
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The drive uses a motor to rotate the media at a high speed
Accesses (reads) the stored information using small devices called
heads
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A ferromagnetic material
If you expose it to a magnetic field it is permanently magnetized
At the gap, the magnetic flux forms a fringe pattern
The flux magnetizes the oxide on the media
During reading, the read head pulls a varying magnetic field across the
gap
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Creates a varying magnetic field in the core and a signal in the coil
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Mar 29—Kernels and Routines,
Bandwidth, UPS, Ports, SATA, USB
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DLL = Dynamic-Link Library
A library of executable functions or data that can be used by a Windows
application
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A DLL can be used by several applications at the same time
Some DLLs are provided with the Windows operating system and
available for any Windows application
Other DLLs are written for a particular application and are loaded with
the application
DLL is Microsoft's implementation of the shared library concept in the
Microsoft Windows and OS/2 operating systems
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A DLL provides one or more functions
A program accesses the functions by creating a static or a dynamic link to
the DLL
A static link remains constant during program execution
A dynamic link is created by the program as needed
Usually have the file extension DLL, OCX (for libraries containing ActiveX
controls), or DRV (for legacy system drivers)
DLL file formats are the same as for Windows EXE files
DLLs can contain code, data, and resources, in any combination.
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Application Program Interface (API)
 A set of routines, protocols, and tools for
building software applications
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A good API makes it easier to develop a program
by providing all the building blocks
A programmer puts the blocks together
Most operating environments, such as MSWindows, provide an API
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Programmers can write applications consistent
with the operating environment
Guarantee that all programs using a common API
will have similar interfaces
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Registry
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A database used by the Windows operating system to store
configuration information
The Registry consists of the following major sections:
 Roots - file associations and OLE information (Object Linking and
Embedding)
 Users Preferences - all preferences set for current user
 User Information - all the current user information for each user
of the system
 Local Machine Settings - settings for hardware, operating
system, and installed applications
 Current Configuration - settings for the display and printers and
other devices
 Dynamic Data - performance data
Most Windows applications write data to the Registry
 You can edit the Registry directly by using the Registry Editor
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regedit.exe provided with the operating system
Errors in the Registry could disable your computer.
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Bandwidth, UPS
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Analog to digital converters
Digital to analog converters
Uninterruptable Power Supplies
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Voltage surges and spikes - Times when the voltage on
the line is greater than it should be
Voltage sags - Times when the voltage on the line is less
than it should be
Total power failure - Times when a line goes down or a
fuse blows somewhere on the grid or in the building
Frequency differences - Times when the power is
oscillating at something other than 60 Hertz
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Ports
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A port serves as an interface between the
computer and other computers or devices
Physically, a port is a specialized outlet to
which a plug or cable connects
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Serial
Parallel
SATA
USB
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Apr 19—LAN, Internet, TCP/IP, DSL,
Cable Modems
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Local area network (LAN)
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A network which connects computers together in
a small geographic region (office, home, etc.)
Designed to share resources on a network
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Example: sharing a printer at home
Can be wired or wireless
Topology: bus, ring, or star
Network model: client/server or peer-to-peer
Physical components: NIC card, wiring
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Ethernet
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Ethernet is the most common LAN
today
Ethernet operates on the physical
layer (layer 1) and data link layer
(layer 2)
Most common installations of
Ethernet (home, office) use:
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Communicate via Ethernet packets
NIC card has MAC address
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CAT5/6 twisted pair cable
RJ-45 connectors
48 bit, represented in Hex
02608CBBDCA7
IEEE assigns unique address
Permanently attached
This is a “layer 2” address
Ethernet Packet
Protocol called Carrier Sense
Multiple Access with Collision
Detection (CSMA/CD)
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Hub vs. Switch vs. Router
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Hub
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Switch
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Broadcasts what it receives on one port to all ports within a single network
Dumb device
Physical layer device (layer 1)
A “smart” hub: performs same function of a hub, just does the job better
A switch reads the MAC address of the packet and transmits the packet to
the port that leads to the node it is addressed to (or can broadcast also)
Data Link layer device (layer 2)
Router
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Connects different networks (i.e. different LANs together) by reading IP
address
Often, when you buy a router it includes a switch
Internet layer device (layer 3)
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Connecting to the Internet
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Modems
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Most recent type of modems are 56K, or V.90 that are able
to carry data at a maximum data rate of 56Kbps
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Digital Subscriber Line (DSL) or xDSL is a technology for sending high
speed digital data across analog telephone lines
 Unlike regular dial-up modems, you do not need to dial up, the
connection is always on
 Also, the phone lines is not held up when connected unlike a modem 
voice and DSL data occupy different frequency bands
 The Ethernet NIC in your computer interfaces to a DSL modem
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Cable Modems: Data is carried over fiber optic cables from the
cable provider to the provider’s distribution hub and then over
standard coaxial cable from the hub to your cable modem
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Both TV signals as well as computer data are carried over the same
cable
A coupler/splitter routes TV data to TV set and computer data to the
cable modem
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The Internet
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History of the Internet
An interconnected system of networks that
connects computers around the world via the
TCP/IP protocol
Interconnected networks
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Circuit Switching
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Public switched telephone network (PSTN) uses circuit
switching
Dedicated resources are allocated along the network for that
particular call
No one else can use those resources, even if
communication is inactive
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Packing Switching
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Internet uses packet
switching
No dedicated resources
allocated
Sender breaks data into
packets
Packets sent across
network, may go different
routes
Receiver reassembles
packets
Simultaneously, many other
senders and receivers using
the same resources
http://williamstallings.com/DCC/DCC7e.html
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Protocol layers and Encapsulation
Layer 5
Application
Layer
Layer 4
Transport
Layer
Layer 3
Internet
Layer
Moves data between networks using routers using an address
Example: Internet Protocol (IP) uses IP address
Layer 2
Data Link
Layer
Moves data within a network using switches using an address
-Example: Ethernet (Data Link Layer) uses MAC address
Layer 1
Physical
Layer
Allows applications to work together
-Example: HTTP, FTP
Ensures reliable transmission, error control
-Example: Transmission Control Protocol (TCP)
Physical connection between machines including
electrical signaling and wiring
Example: Ethernet (Physical Layer)
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Following an IP packet
Router 2
Router 4
You in
Virginia
Router 1
Router 6
Server
In
Australia
Router 3
Router 5
-Routers do not alter IP datagrams
-Network interface layer headers
and footer change from router to router
Application
Layer
Application
Layer
Transport
Layer
Transport
Layer
Internet
Layer
Internet
Layer
Internet
Layer
Internet
Layer
Internet
Layer
Internet
Layer
Internet
Layer
Internet
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Physical
Layer
Physical
Layer
Physical
Layer
Physical
Layer
Physical
Layer
Physical
Layer
Physical
Layer
Physical
Layer
You in
Virginia
Router 1
Router 2
Router 3
Router 4
Router 6
Server
In
Australia
GMU IT 212 - Spring 2007
Router 5
51
Apr 26—Displays, I/O, Portable
Computers, Multimedia

CRT vs LCD vs Plasma




CRT uses electron gun which
hits phosphor-coated screen
LCD uses liquid crystals which
twist light depending on electric
field; light passes through
polarizing filters
Plasma uses gas which emit
photons excited by electric
field; photons hit phosphors to
produce colors
DLP uses a spinning wheel
with micro-mirrors for
projection
GMU IT 212 - Spring 2007
52
Input/Output Devices




Keyboard
 Scan codes
Mouse
 Mechanical Mouse
 Optical Mouse
 Touchpad
 Pointing Stick
Speech recognition
 Enrollment of phonemes
 Two steps: acoustic recognizer, then natural language
component
Scanners
 Use CCDs
 OCR character recognition software
GMU IT 212 - Spring 2007
53
Notebook PCs


Objectives
 Minimize size, weight, power consumption for portability
 Constraints: viewing area, keyboard, mouse, power capacity
Realities
 Typically 2x cost of comparable PC


Upgrading is difficult, if not impossible




lags desktop capabilities
economically practical?
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
PC Cards: expandability, upgradeability
PDAs: input interface issues
GMU IT 212 - Spring 2007
54
Multimedia

Sound card



Video card


MIDI—only instructions on how to play the audio file is stored,
not the audio recordings themselves
MP3—two steps to reduce file size: perceptual coding then
lossless compression
AVI format: interweave video and audio
DVDs in MPEG format



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
GMU IT 212 - Spring 2007
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IT212 How Computers Work - George Mason University