Technical IssuesTechnical Issues

for the Internet

Computers are DigitalComputers are Digital

• 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 NumbersHexadecimal Numbers

• Can convert bytes to hexidecimal

• http://www.cookwood.com/cookwood/html4_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 IComputer 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 SystemOperating 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 SystemsPC Operating Systems

• WindowsWorks on all IBM PCs and ClonesSeparate from hardwareStability/virus issues throughout history

• Macintosh (based over UNIX)One computer with intergrated OSLess software availableMore graphic oriented

• UNIX/LINUXOpen sourceVery reliable

Internal Hardware: CPUInternal 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: MotherboardInternal Hardware: Motherboard

• Motherboard: includes CPU, memory, power connection, ports. Different sizes have different uses.

Bus Speed: information in and out of CPU

Internal Hardware: MemoryInternal 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 DrivesHard 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 MultimediaMonitors 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

ModemsModems

• 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 ProtocolsFax Protocols

• Fax standards include page size, resolution, error correction, and compression

Methods to Connect to InternetMethods to Connect to Internet

• 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/IPTCP/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 IHome Networking I

• 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 IIHome 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 IIIHome 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 PhonesCell 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.

FirewallsFirewalls

• 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.