Computing and Networks Week 1 LBSC 690 Information Technology Goals By the end of this class, you will Understand what makes stupid computers seem smart Have ways to think about space, time and speed Know how the Internet got its name Teaching Theater Introduction Logging on
Userid and password are your university account Directories Your personal directory (to save notes) is at M: Nothing on the C: drive is saved!!! Getting to notes you take from home http://ttclass.umd.edu Agenda What computers do How they do it About the course
A Very Brief History of Computing Hardware Mechanical: essentially a big adding machine Analog: designed for calculus, limited accuracy Digital: early machines filled a room Microchips: designed for missile guidance Software Numeric: computing gun angles Symbolic: code-breaking Commercial Developments
Mainframes (1960s) IBM Minicomputers(1970s) DEC Personal computers (1980s) Apple, Microsoft Networks (1990s) Web Convergence (2000s)
Cell phone/PDA, HDTV/Computer, Source: Wikipedia Source: Wikipedia Source: Wikipedia Source: Wikipedia Source: Wikipedia Source: Wikipedia
The Big Picture Processor Network Memory Binary Data Representation Example: American Standard Code for Information Interchange (ASCII) 01000001 01000010
ps 10-12 = 1/1,000,000,000,000 femtosecond fs 10-15 = 1/1,000,000,000,000,000 The Storage Hierarchy Speed, cost, and size:
You can easily get any 2, but not all 3 Fast memory is expensive So large memory is slow! But fast access to large memories is needed Solution: Keep what you need often in small (fast) places Keep the rest in large (slow) places Get things to the fast place before you need them Best of Both Worlds
Small, but fast + = Is Large and seems fast Large, but slow Think about your bookshelf and the library Locality Spatial locality:
If the system fetched x, it is likely to fetch data located near x Temporal locality: If the system fetched x, it is likely to fetch x again System Architecture Keyboard Sound Card Video Card
Mouse Input Controller System Bus Front Side Bus L2 CPU
L1 Cache RAM Motherboard Hard Drive CD/ DVD
USB Port Everything is Relative The CPU is the fastest part of a computer 3 GHz Core 2 Duo = 6,000 MIPS 3 operations per processor every nanosecond Cache memory is fast enough to keep up 128 kB L1 cache on chip (dedicated, CPU speed) 4 MB L2 cache on chip (shared, CPU speed) RAM is larger, but slower
1 GB or more, ~6 ns Units of Size Unit Abbreviation Size (bytes) bit b 1/8
TB 240 = 1,099,511,627,776 petabyte PB 250 = 1,125,899,906,842,624 The Storage Hierarchy Type Registers
Cache RAM Hard drive Speed ~300 ps ~1 ns ~10 ns ~10 ms Size 256 B 4 MB
1 GB 100 GB Cost Very expensive Expensive Cheap Very cheap Solid-State Memory ROM Does not require power to retain content Used for Basic Input/Output System (BIOS)
Cache (Fast low-power Static RAM) Level 1 (L1) cache: small, single-purpose Level 2 (L2) cache: larger, shared (Dynamic) RAM (Slower, power hungry) Reached over the Front-Side Bus (FSB) Flash memory (fast read, slow write EEPROM) Reached over USB bus or SD socket Used in memory sticks (non-volatile storage) Source: Wikipedia
System Architecture Keyboard Sound Card Video Card Mouse Input Controller
System Bus Front Side Bus L2 CPU L1 Cache RAM
Motherboard Hard Drive CD/ DVD USB Port Rotating Memory Fixed magnetic disk (hard drive)
May be partitioned into multiple volumes In Windows, referred to as C:, D:, E:, In Unix, referred to as /software, /homes, /mail, Removable magnetic disk Floppy disk, zip drives, Removal optical disk CDROM, DVD, CD-R, CD-RW, DVD+RW, How Disks Work Extracted From Shelly Cashman Vermatts Discovering Computers 2004
Trading Speed for Space Hard disk is larger than RAM but much slower typical: 10 ms access time, 100 GB (at 5400 rpm) One thousand times larger than RAM 10 million times slower than the CPU! The initial access is the slow part Subsequent bytes sent at 17 MB/sec (60 ns/byte) As virtual memory, makes RAM seem larger But too little physical RAM results in thrashing
Discussion Point: Moores Law Processing speed doubles every 18 months Faster CPU, longer words, larger cache, more cores Cost/bit for RAM drops 50% every 12 months Less need for virtual memory Cost/bit for disk drops 50% every 12 months But transfer rates dont improve much Why???? Breaks
Typically, two breaks 10 minute break after the first hour 5 minute break after the second hour No food or drink in the teaching theater Whos faster? Intel Pentium 4 (2004): 3.80 GHz Intel Core 2 Duo (2008): 2.6 GHz More cores! RAID-5
Disks can fail in two ways: Bad sectors (data sectors, directory sectors) Mechanical failure RAID-5 arrays stripe blocks across disks Parallel data transfer is faster than serial ~30% parity allows reconstruction if one disk fails Tape Backup Tapes store data sequentially Very fast transfer, but not random access Used as backup storage for fixed disks
Weekly incremental backup is a good idea With a complete (level zero) monthly backup Used for archival storage Higher data density than DVDs Discussion Point: Migration What format should old tapes be converted to? Newer tape CD DVD How often must we refresh these media?
How can we afford this? Discussion Point: Whats Special About Computers? Course Goals Conceptual Understand computers and networks Appreciate the effects of design tradeoffs Evaluate the role of information technology Practical Learn to use some common tools
Solve a practical problem Develop a personal plan for further study Some Motivating Questions What are the technical implications for: Privacy? Copyright? How will digital repositories develop? How will they interact with distance education? What are the implications for archives? How might electronic dissemination impact:
Roles of authors, publishers, and readers? Access by disenfranchised populations? Some LBSC Courses on IT 708E 708Q E-Government 708T 708X Transformational Technologies
715 733 Knowledge Management 790 793 Programming for User Interfaces 795 796
Human-Computer Interaction Digital Preservation E-Discovery Networks Database Design Information Retrieval Systems Instructional Staff Professor: Dr. Doug Oard Offices: HBK 4121G/AVW 3145 Email: [email protected] (finds me anywhere)
Provide conceptual structure Practicum sessions, homework, project Provide hands-on experience Quiz, exams Measure progress The Grand Plan Computing Databases
Multimedia Search Midterm Social Software Life Cycle Project
Policy Final A Personal Approach to Learning Work ahead, so that you are never behind Find new questions everywhere Then find the answers somewhere Enrich your practical skills relentlessly Pick topics you want to learn more about Start thinking about your project soon Pick partners with complementary skills
Obtaining Recordings All classes recorded Fixed camera angle with screen in field of view Microphones in the ceiling Usually available over the Internet Postage-stamp video, some audio distortion Useful for seeing what slide we were on Videotapes available outside my office Please dont take for more than 24 hours
Getting From Here to There What you need to know Midterm Quiz y d o b o N s! i
h t s e do What I did in Grad School What you know now Grading 35-38% individual work Exams: 25% for the best, 10% for the other
12-15% your choice (individual or group) 3% each for best 5 of the 7 homework/quiz 40% working in 3-person project teams 10% for demonstrated thought leadership In class, on the mailing list, in your groups Some Observations on Grading One exam is worth more than all the homework Message: Use the homework to learn the material Midterm grades predict final grades well Message: Develop sound study skills early
You need not be good at everything to get an A But you do need to be excellent at several things The Fine Print Group work is encouraged on homework But you must personally write what you turn in Deadlines are firm and sharp Allowances for individual circumstances are included in the grading computation Academic integrity is a serious matter
No group work during the exams or the quiz! Scrupulously respect time limits Course Materials Readings Optional Textbook Daily access to a networked computer! Computing at Maryland Computer Labs HBK 2018 (posted hours) PG2 WAM lab (24 hours) Need an OIT LPCR account for printing
Sailor dial-in access http://www.sailor.lib.md.us/help/ppp Homework Goals Think about relative speed and relative size Interpret specifications for computer systems Try some back of the envelope calculations Some helpful hints: There is a calculator in Windows accessories If youre rusty on math, the TA can help in lab Team Exercise
Form into groups of 4 Be sure you have someone who has used Excel before in your group Answer question 1(d) from the Fall 1996 final exam (available on the course Web site) Network Computers and devices connected via Communication devices Transmission media Why Network?
Sharing data Sharing information Sharing hardware Sharing software Increasing robustness
Facilitating communications Facilitating commerce Packet vs. Circuit Networks Telephone system (circuit-switched) Fixed connection between caller and called High network load results in busy signals Internet (packet-switched) Each transmission is routed separately High network load results in long delays Packet Switching
Break long messages into short packets Keeps one user from hogging a line Route each packet separately Number them for easy reconstruction Request retransmission for lost packets Unless the first packet is lost! Networks of Networks Local Area Networks (LAN) Connections within a room, or perhaps a building
Wide Area Networks (WAN) Provide connections between LANs Internet Collection of WANs across multiple organizations Local Area Networks Within a campus or an office complex Short-distance lines are fast and cheap Fast communications makes routing simple Ethernet is a common LAN technology All computers are connected to the same cable
Ordinary phone lines can carry 10 Mb/sec 100 Mb/s connections require special cables 1 Gb/s connections require special switches Every host broadcasts everything to all others Collisions limit throughput to about 50% utilization Shared Network All attach to the same cable Ethernet and cable modems Transmit anytime Collision detection
Automatic retransmission Inexpensive and flexible Easy to add new machines Robust to computer failure Practical for short distances Half the bandwidth is wasted Switched (Star) Network All attach directly to a hub Switched Ethernet Digital Subscriber Lines (DSL)
Higher cost Line from hub to each machine Hub must handle every packet Hub requires backup power Much higher bandwidth No sharing, no collisions Allows disks to be centralized Local Area Networks CSS www
rac2 rac3 rac4 ttclass PLS sam kim ann
dove joe HBK Wireless Networks Radio-based Ethernet Effective for a few rooms within buildings Access Point gateways to wired networks Available throughout most of the Maryland campus Commercial providers offer hot spots in airports, etc.
WiFi WLAN is available in several speeds IEEE 802.11b: 10Mb/s (good enough for most uses) IEEE 802.11g: 54Mb/s (required for wireless video) IEEE 802.11n: 248Mb/s (and longer range) Computer-to-computer networks are also possible Bluetooth is the most common (very short range) Wide Area Networks Campus, regional, national, or global scale Expensive communications must be used well Limiting to two hosts allows 100% utilization
Routing is complex with point-to-point circuits Which path is shortest? Which is least busy? Marylands Campus Network Elsewhere in CSS www rac2 rac3 rac4
ttclass CSS 1410 sam kim ann dove joe HBK The Internet Global collection of public IP networks
Private networks are often called intranets Independent Each organization maintains its own network Cooperating Internet Protocol (IP) address blocks Domain names
World-Wide Web Consortium (W3C) Computer Emergency Response Team (CERT) Overview A Short History of the Internet 1969: Origins in government research Advanced Research Projects Agency (ARPAnet) Key standards: UDP, TCP, DNS 1983: Design adopted by other agencies Created a need for inter-network connections Key standards: IP
1991: World-Wide Web added point-and-click Now 150 million Internet hosts Key standards: HTTP, URL, HTML, XML Internet Web Internet: collection of global networks Web: way of managing information exchange More details on this next week There are many other uses for the Internet File transfer (FTP) Email (SMTP, POP, IMAP)
http://www.geog.ucl.ac.uk/casa/martin/atlas/isp_maps.html Thinking About Speed Speed can be expressed two ways: How long to do something once? Memory speed measured as access time How many things can you do in one second? Processor speed measured in instructions per second Convenient units are typically used 10 microseconds rather than 0.00001 seconds
Some Definitions Latency The amount of time it takes data to travel from source to destination Bandwidth The amount of data that can be transmitted in a fixed amount of time The Complete Picture Two parts of moving data from here to there: Getting the first bit there
Getting everything there Fundamentally, theres no difference: Moving data from the processor to RAM Saving a file to disk Downloading music from a server in China Before You Go On a sheet of paper, answer the following (ungraded) question (no names, please): What was the muddiest point in todays class?
Roman Republic destroyed. 2nd Triumvirate. Octavian, Marc Antony and Lepidus . Ruled for 10 years. Jealousy and violence. Lepidus retires, Octavian and Marc Antony rivals. Octavian rules; becomes Augustus Caesar. PaxRomana(207 years) After Augustus death, empire remained stable .
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