Welcome to CMPE003 Personal Computers: Hardware and Software

1. Welcome toCMPE003Personal Computers: Hardware and Software Dr. Chane Fullmer Fall 2002 UC Santa Cruz

2. Midterm #2Review

3. Types of Storage • Magnetic Disk Storage • Optical Disks • Magneto-optical • CD-ROM • CD-R • CD-RW • DVD-ROM • Magnetic Tape Storage

4. Data Compression • Why use? • Squeeze big files onto small disks • Speed up data transfer of files • Goal – Remove redundancy (minimize size) • Reduce to the minimal number of bits to store data • Techniques • Remove all extra space characters • Substitutes a smaller data string for a frequently occurring set of characters • Software uses formula to determine how to compress • Different models used based on content (text, image, etc) • Must be decompressed to be used again

5. Logical Layout of a DiskTrack • Concentric circles • Passes under read/write head as disk rotates • 1.44 MB diskette has 80 tracks on each surface • Numbered 0  79 • Each track stores the same amount of data

6. Logical Layout of a DiskSector • Pie-shaped division of track • Holds a fixed number of bytes (512 bytes) • Cluster • Adjacent sectors treated as a unit of storage • Fixed number (2-8 sectors) • Minimum space allocated to a file

7. Logical Layout of a DiskCylinder • Same track on each platter • Store files across multiple platters • Reduces access time

8. Disk DriveRead / Write Operation • Disks rotate • Access arm moves read/write head • Read / write operation begins and continues until complete • Data is transferred to/from memory

9. Access Time Components • Seek time • Travel time for moving heads over track • Head switching • Turning on correct head • Rotational delay • Waiting for sector to arrive under head (Avg ½ revolution) • Data transfer rate • Read/write bits on disk platter • Depends on density and rotational speed

10. Disk Caching • Required data read from disk into memory • Adjacent data read into disk cache (special area of memory) • Program encounters a read instruction • Checks disk cache • If present, no physical read is required • If not present, read from disk

11. RAID Redundant Array of Independent Disks

12. CD-ROMCompact Disk Read-Only Memory • High capacity portable • Read multiple times • Cannot record • Capacity – up to 680+ MB • (450 standard 3 ½ inch diskettes) • Used for software distribution

13. CD-RCompact Disc-Recordable • Cheap! – < 5 cents – or even free  • Labels are the expensive part now • High capacity • Portable • Write once • Cannot be rewritten or changed • Read multiple times • CD-R drive • CD-ROM drive

14. CR-RWCompact Disk-Rewritable • High capacity • Portable • Read multiple times • Record multiple times • Some compatibility problems reading CD-RW disks on CD-ROM drives

15. Backup Systems • Prevent data loss • Fire • Natural disaster • Electromechanical failures of disk • User introduced errors • Software errors • Accidental data deletion • Store data in more than one place • Important data must be kept “offsite”

16. Bit Rot How long is my data good? • Not forever…… • Bit rot occurs in all media • Bit rot is a degradation of the medium itself over time • Worst  Best.. • Floppy 0 - 2 yrs • Tape 2 – 20 (with ECC) • Hard Disk 5 yrs • CD-RW 5 - 20 ? • CD-R 5 - 20 ? • DVD ???

17. Networking • Uses communication equipment to connect two or more computers and their resources • Can be PC based • Allows connected users to share data and resources • LAN – Local Area Network • shares among users in close proximity • WAN – Wide Area Network • shares among users who are geographically distant

18. Data Transmission • Digital lines • Sends data as distinct pulses • Need digital line • Analog lines • Sends a continuous electrical signal in the form of a wave • Conversion from digital to analog needed • Telephone lines, coaxial cables, microwave circuits

19. Modulation • Modulation means imposing information on an electrical signal (called the carrier) Amplitude Modulation Frequency Modulation Phase Modulation

20. Dialup Modem • MODEM -- Mo(dulator)/Dem(odulator) • Modulate • Convert from digital to analog • Demodulate • Convert from analog to digital • Speeds up to 56,000 bps (56K)

21. Network Topology • Physical layout • Star • Ring • Bus • Node – any device connected to the network • Server • Computer • Printer • Other peripheral

22. Network Topology • Collisions of data packets causes them to fail, and they must be retransmitted • Star • Collisions at center hub/node • Ring • No collisions, traffic flows in one direction coordinated by tokens • Bus • Collisions can occur all along the bus

23. Star • Central hub • All messages routed through hub • Hub prevents collisions • Node failure – no effect on overall network • Hub failure – network fails

24. Ring • Travel around circular connection in one direction • Node looks at data as it passes • Addressed to me? • Pass it on if not my address • No danger from collisions • Node failure – network fails

25. Bus • Single pathway • All nodes attached to single line • Collisions result in re-send • Node failure – no effect on overall network

26. Basic Components to build a Network Computer (PC) Network Interface Card (NIC) Network Cables

27. LANs • LANs A computer communication technology is classified as a Local Area Network (LAN) if it provides a way to interconnect multiple computers across short distances. • Modern day LANs are inexpensive, reliable and convenient to install and manage

28. Wide Area Networks • A WAN differs from a disjoint set of transmission lines because of the inclusion of a special computer (Gateway) at each site that connects to the transmission lines and keeps communication independent of the computers that use the WAN • WANs cover large geograhpic areas.

29. Routing • What is a router? • A dedicated computer • Special software • Restarts automatically on power up • Goal is to forward packets from one network to another – quickly, efficiently and correctly • Process is called routing • Computers are called routers

30. Routers.. • Routers – Building blocks of the Internet The Internet is not a conventional network. It consists of thousands of computer networks interconnected by dedicated special purpose computers calledrouters • Routers can interconnect LANs and WANs

31. Protocols – Rules to live by… • Set of rules governing the exchange of data • Assists with coordination of communications • Was message received properly ? • TCP/IP • Transmission Control Protocol / Internet Protocol • Internet standard • All computers in world speak same language

32. Dominant protocol Bus or star topology Uses CSMA/CD CSMA/CD Carrier sense multiple access with collision detection Tries to avoid 2 or more computers communicating at the same time Computer listens and transmits when cable is not in use Collision results in waiting a random period and transmitting again Performance degrades with multiple collisions Ethernet

33. The Early Years • The DoD funded network research in the early ’70s through (D)ARPA creating various network technologies, including a research WAN called ARPANET.

34. The Early Years • ARPANET allowed researchers the opportunity to build a working test-bed for networking ideas. • Solved incompatibility issues • Solved interoperability issues • Created an internetwork of LANs and the WANs • The Internet is born

35. The Early Years • The ANS Backbone (Advanced Networks and Services) • Consortium of MCI, IBM & MERIT • Allowed the government to begin privatization of the Internet • 1992 – WAN was built to serve as the Internet backbone • ANSNET, 30 times NSFNET capacity

36. The Early Years… • Internet Software • Internet Protocol (IP) • Provides basic communication • Handles the addressing and routing • Transmission Control Protocol (TCP) • Provides services for applications to communicate • Packetizes message, reassembles message at the destination • The “TCP/IP Internet Protocol Suite” • aka TCP/IP

37. The Early Years • The IETF (Internet Engineering Task Force) • Originally chartered for short-term Internet development. • Now is responsible for most of the Internet technical development • Working groups meet and create the RFCs • Manet, ipsec, tcp…

38. FTP ClientFile Transfer Protocol • Download files to your local computer • Upload files to another computer • Requirements to download file • Permission to download from a site • File is available for copying • Anonymous FTP – do not need to identify yourself to the remote computer • (But we do know your IP address)

39. Telnet/SSH • Use your PC as a terminal providing remote access to another computer • Permits • Log on to a host • Use as if you are sitting at a local terminal • Need account on the host system • Telnet software required (provided with most browsers) • SSH available free on-line – must be installed

40. Dr. Tim Berners-Lee • 1990 • Perceived a spider’s web of computers with links from computer to computer • CERN site • Dr. Berners-Lee’s physics laboratory • Birthplace of the World Wide Web • Easy movement due to links • Hypertext • Hyper-region

41. httphypertext transfer protocol • HTTP is the protocol of Web based traffic

42. URLUniform Resource Locator • Unique address of a web page or file on the Internet • Case-sensitive http://domain-name.top-level-domain/last-section

43. EtailSavings to retail business No physical store building People time

44. EtailAdvantage to Consumer • Any time shopping • No need to dress and travel – shop naked!! • Saves time • Provides simple means to comparison-shop • Anyplace • Contributes to competition

45. Web-based Business • Make business look large • Many products can be offered since no inventory • No physical space to reflect size

46. Internet Speed • Bandwidth • A measure of link capacity • Increase bandwidth • Satellite • ISDN • DSL (Digital Subscriber Line) • Cable modem • For business • T3, etc…

47. Payments • Finalize order by • Phone • Fax • Call with credit card number • Enter credit card number • Security • Communication between buyer and retailer is encrypted • Use SSL (Secure Sockets Layer) protocol and generate the message “our secure server”

48. Streaming • Hear and see digitized content as it is downloaded • Audio • Video • Animation • Uses substantial bandwidth • Quality of content • Speed of connection • Internet traffic • Performance will improve as bandwidth improves • Content is displayed using Plug-ins

49. Unicasting Unicasting • Send multiple computers copies of files individually • Wastes bandwidth as you are sending the same file over and over

50. Multicasting • Broadcast • Send one copy of the file to every computer on the network • Wasteful – some users do not need the file • Compromises security • Multicasting • Send one copy of the file and it is directed only to the appropriate recipients