Transcript Technical Issues

Technical Issues
for the Internet
Computers are Digital
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All information is stored in bits.
Each bit is on/off, true/false, 1/0.
8 bits=1 byte
8 bits can store numbers up to 255
16 bits can store numbers up to 65535
32 bits can store numbers up to 4,294,967,295
Hexadecimal Numbers
• Can convert bytes to hexidecimal
• http://www.cookwood.com/cookwood/html
4_examples/4files/colorhex/hexchart.html
• Useful for choosing colors in HTML.
• 3 hexidecimal numbers strung together
representing amount of red, green, and blue.
Computer Fundamentals I
• BIOS: basic input/output system
• BIOS controls basic operations of computer,
including interaction with keyboards, hard
drives, etc.
• Need drivers for added external devices
• Interrupt channels linked to each device and
receive a signal when a device’s status
changes (a key is pressed)
Operating System
• Controls processors, devices, memory
management, and applications.
• RTOS (real time OS): car, dryer
• Single User/Single Task-PDA
• Single User/Multitask - computer OS
PC Operating Systems
• Windows
 Works on all IBM PCs and Clones
 Separate from hardware
 Stability/virus issues throughout history
• Macintosh (based over UNIX)
 One computer with intergrated OS
 Less software available
 More graphic oriented
• UNIX/LINUX
 Open source
 Very reliable
Internal Hardware: CPU
• Processor: Speed and Chip type
• Made up of transistors, on-off switches
• Different chips control interface with other
devices, cache, integers, and floating-point
numbers.
• Cache: short term memory
• Early chips included 386,486,586
• Followed by Celeron and Pentium series
• For Macintosh, progression from 68000 series to
G3-G4-G5.
• Speed measured in GHz (formerly MHz)
Internal Hardware: Motherboard
• Motherboard: includes CPU, memory,
power connection, ports.
Different sizes have different uses.
Bus Speed: information in and out of CPU
Internal Hardware: Memory
• RAM
• DRAM and SRAM
• ROM
• A memory chip has a speed
• SIMM (30 or 72 pin)/DIMM(168 pin)/RIMM
(184 pin)
Hard Drives
• Internal or External
• Amount of storage memory
• Speed of transfer (RPM and seek time)
• Many alternatives today (some very small)
• Connect via SCSI or USB or Firewire
• Also, CD-ROM (650MB), DVD-ROM (4.7 GB)
drives, ZIP (100, 250, 750MB), floppy disks.
Monitors and Multimedia
• Monitors smaller the pitch, the better (.28 is
average)
• Resolution varies: 640x480, 800x600,
1024x768, 1280x854
• Video and Sound Cards
• Can be upgraded from standard
• Built into Macintosh systems
Modems
• Modulator/Demodulator
• Methods to Convert to analog include amplitude,
frequency, or Pulse Code (for digital to digital only)
• Simplex/half duplex/duplex
• Use Command Sets (for commands like “off hook” and
handshake protocols: speed and error-checking)
• Current standard V.90 and V.92
• V.90 is 56kbps
• V.92 adds modem on hold & quick connect
• Internal or External via Serial, USB
Fax Protocols
• Fax standards include page size, resolution,
error correction, and compression
Methods to Connect to Internet
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Voiceband (56 Kbps, but max 53.3 Kpbs in U.S.)
Broadband (8+ Mbps)
Telephone Modem
DSL
Cable Modem
Satellite
Cell Phone
Wireless
Web TV
(LAN: local area network)
(Online Services)
TCP/IP
• Transmission Control Protocol/Internet Protocol
• TCP sorts information into packets (up to 1500 characters
each)
• IP addresses packets and reforms them (validating with a
“checksum”.)
• IP address = 32 bit number (four 8 bit numbers separated
by dots): 4,294,967,295
• Static and Dynamic IP addresses
• IP address uses the Domain Name Servers located
throughout internet to connect to the correct URL.
• PPP = Point-to-Point protocol. Full duplex controlling
sign-on and connecting through ISP
• Client-Server Model
Home Networking I
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Hub
Switch
Router: Static Routing vs. Dynamic Routing
Interior and Exterior Routers
Router assigns local IP addresses between
192.168.0.0 and 192.168.255.255
Home Networking II
• Connect via Ethernet (or USB): limited to
100 meters, vulnerable to some electrical
appliances: heaters, fluorescent lights
• Connect via phone line
• Connect via electrical outlets
Home Networking III
• Wireless: 802.11a, 802.11b, 802.11g. “b” and “g”
are compatible.
• Wireless Uses: microwave oven, radio, home
control, security, refrigerator, e-mail appliance
• How a wireless network works…
• Basic Service Set
• Extended Service Set
• Bluetooth (for Palm OS, etc.)
Cell Phones
• Cell phones can connect to the internet by
calling a base station, or nearest cellular
antenna, which has an internet connection.
• Web pages must be converted to WML
(wireless markup language) from HTML
• PDAs work in a similar way. They connect
wirelessly or through a desktop computer,
but must have HTML converted to be read
on PDA screen.
Firewalls
• Screens incoming packets.
• Can limit the IP addresses a packet comes
from (or goes to).
• Can limit the type of program allowed into
or out of the computer
• Can limit the type of communication (e.g.,
only allowing e-mail)
• There may be several layers of firewalls for
corporate and government servers.