Technical Issues for the Internet

Computers 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 bits can store numbers up to bits can store numbers up to 4,294,967,295

Hexadecimal Numbers Can convert bytes to hexidecimal 4_examples/4files/colorhex/hexchart.htmlhttp:// 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 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 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 Hub Switch Router: Static Routing vs. Dynamic Routing Interior and Exterior Routers Router assigns local IP addresses between and

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: a, b, g. “b” and “g” are compatible. Wireless Uses: microwave oven, radio, home control, security, refrigerator, 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 ) There may be several layers of firewalls for corporate and government servers.