Computing Week 1 LBSC 690 Information Technology

Teaching Theater Introduction Logging on –Userid and password are your university account Key directories –Shared class materials are on N:\SHARE –Your personal directory is at M: Taking notes

Agenda Looking backwards What “computers” do How they do it About the course

Goals By the end of this class, you will… –Have a basic understanding of computers –Know how to think about “space,” “time” and “speed” –Understand of how computers store data and move data around

A Very Brief History of Computing Hardware: all developed for the government –Mechanical: essentially a big adding machine –Analog: designed for calculus, limited accuracy –Digital: early machines filled a room –Microchips: designed for missile guidance Software: initial applications were military –Numeric: computing gun angles –Symbolic: code-breaking

Commercial Developments Mainframes (1960’s) –IBM Minicomputers(1970’s) –DEC Personal computers (1980’s) –Apple, Microsoft Networks (1990’s) –Web Convergence (2000’s) –Cell phones/PDA, TV/Computer, …

Hardware Processing Cycle Input comes from somewhere –Keyboard, mouse, microphone, camera, … The system does something with it –Processor, memory, software, network, … Output goes somewhere –Monitor, speaker, robot controls, …

Discussion Point: What’s Special About Computers? Digital content –Perfect copies Programmed behavior –Speed –Repetition –Complexity

The Big Picture Processor Memory Network

Computer Hardware Central Processing Unit (CPU) –Intel Xeon, Motorola Power PC, … Communications “Bus” –FSB, PCI, ISA, USB, Firewire, … Storage devices –Cache, RAM, hard drive, floppy disk, … External communications –Modem, Ethernet, GPRS, , …

Extracted From Shelly Cashman Vermatt’s Discovering Computers 2004

Thinking About Transfer Time Total “transfer time” is what counts –Time for first bit + time between first and last bits For long distances, first bit time is important –California: 1/80 of a second (by optical fiber) –London:1/4 of a second (by satellite) For large files, bits per second dominates –Number of bits per second is limited by physics Inside computers, bits per second dominates

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

Discussion Point What are the latency and bandwidth requirements for the following applications: –Streaming audio (e.g., NPR broadcast over Web) –Streaming video (e.g., CNN broadcast over Web) –Audio chat –Video conferencing

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 “ seconds” When comparing speeds, convert units first!

The Storage Hierarchy The problem: –Fast memory is expensive So large memory is slow! –But fast access to large memories is needed The 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… Large, but slow… Large and fast?! Think about your bookshelf and the library…

System Architecture CPU RAM Hard Drive CD/ DVD Cache Motherboard System Bus Video Card Input Controller KeyboardMouse Sound Card USB Port L1 L2 Front Side Bus

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 Time UnitAbbreviationDuration (seconds) secondsec/s1 millisecondms10 -3 = 1/1,000 microsecond ss = 1/1,000,000 nanosecondns10 -9 = 1/1,000,000,000 picosecondps = 1/1,000,000,000,000 femtosecondfs = 1/1,000,000,000,000,000

Units of Frequency UnitAbbreviationCycles per second hertzHz1 kilohertzKHz10 3 = 1,000 megahertzMHz10 6 = 1,000,000 gigahertzGHz10 9 = 1,000,000,000

Units of Size UnitAbbreviationSize (bytes) bitb1/8 byteB1 kilobyteKB2 10 = 1024 megabyteMB2 20 = 1,048,576 gigabyteGB2 30 = 1,073,741,824 terabyteTB2 40 = 1,099,511,627,776 petabytePB2 50 = 1,125,899,906,842,624

The Storage Hierarchy TypeSpeedSizeCost Registers~300 ps256 BVery expensive Cache~1 ns4 MBExpensive RAM~10 ns1 GBCheap Hard drive~10 ms100 GBVery cheap

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 Insight behind the storage hierarchy: –Move important data from slow, large memory to fast, small memory

“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)

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

Introductions Over break: –Pair up with one person you don’t yet know –Introduce yourselves to each other After break: –Introduce your partner to us in 30 seconds –Name, background, goals, one interesting thing

System Architecture CPU RAM Hard Drive CD/ DVD Cache Motherboard System Bus Video Card Input Controller KeyboardMouse Sound Card USB Port L1 L2 Front Side Bus

“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 Vermatt’s 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”

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

Discussion Point: Moore’s Law Processing speed doubles every 18 months –Faster CPU, longer words, larger L1 cache Cost/bit for RAM drops 50% every 12 months –Small decrease in feature size has large effect Cost/bit for disk drops 50% every 12 months –But transfer rates don’t improve much

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)

RAID-5 Disks can fail in two ways: –Bad sectors (data sectors, directory sectors) –Mechanical failure RAID-5 arrays “stripe” blocks across disks –~30% “parity” allows reconstruction if one disk fails “Parallel” data transfer is faster than “serial” –“RAID-0” uses striping for speed, but without parity

… … Errors How Parity Works Encoded Data (4096 possible values) Original Data (256 possible values)

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 DVD’s

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?

Types of Software Application programs (e.g., Internet Explorer) –What you normally think of as a “program” Compilers and interpreters (e.g., JavaScript) –Allow programmers to create new behavior Operating system (e.g., Windows Vista) –Moves data between disk and RAM (+lots more!) Embedded program (e.g., BIOS) –Permanent software inside some device

Installing Applications Copy to a permanent place on your hard drive –From a CD, the Internet, … Installs any other required programs –“DLL” files can be shared by several applications Register the program’s location –Associates icons/start menu items with it –Configures the uninstaller for later removal Configure it for your system –Where to find data files and other programs

Discussion Point: What’s a Virus? Characteristics –Initiation –Behavior –Propagation Spyware Detection

Graphical User Interfaces Easy way to perform simple tasks –Used to start programs, manage files, … –Relies on a physical metaphor (e.g., a desktop) Built into most modern operating systems –Windows XP, Mac OS-X, Unix X-windows Application programs include similar ideas –Point-and-click, drag and drop, …

Cursor-based Interfaces Useful for specifying complex operations –Or when graphical display is impractical Available in most operating systems –SSH connection to WAM –Command window in Windows XP

Summary Speed, cost, and size: –You can easily get any 2, but not all 3 –Computers use caching as a compromise strategy Hardware and software work synergistically –Our focus will be on software and the Internet –But understand hardware abilities and limitations

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 708EE-Government 708QDigital Preservation 708TTransformational Technologies 715Knowledge Management 733Networks 790Building User Interfaces (programming) 793Database Design 795Human-Computer Interaction 796Information Retrieval Systems

Instructional Staff Professor: Dr. Doug Oard –Offices: HBK 4121G/AVW 3145 – (finds me anywhere) Teaching Assistant: Rebekah Fairbank –Office: HBK 4120 –Lab time+location TBA – rlf45 (at) umd.edu Teaching Theater Technician

Approach Readings –Provide background and detail Class sessions –Provide conceptual structure Outline notes provided in class Slides and videotapes available Homework, lab sessions, project –Provide hands-on experience Quiz, exams –Measure progress

The Grand Plan Networking HTML/XML Multimedia ComputersHCI Search CMC Web Life Cycle Policy Databases Programming Web Databases Midterm Project Final Quiz

A Personal Approach to Learning Work ahead, so that you are never behind Ask questions about the readings Augment practical skills with outside resources Pick topics you want to learn more about Start thinking about your project soon –Pick partners with complementary skills

Getting From Here to There What you know now What you need to know Quiz MidtermWhat I did in Grad School Nobody does this!

Syllabus Master the tools in the first 7 weeks –2 readings and one homework most weeks Explore integrating issues the last 7 weeks –1 reading each week + the project

Grading 35-38% individual work –Exams: 25% for the best, 10% for the other 12-15% group work, in any groups you like –3% each for best 5 of the 7 homework/quiz 40% group work, in 3-person project teams –30% for the project, 10% for presentation+report 10% “class” participation

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! –Don’t discuss exam until all sections are done

Course Materials Textbook Supplemental readings Daily access to a networked computer! A USB memory stick

Computing at Maryland Computer Labs (IBM, Mac) –PG2: 24 hr WAM lab Need an OIT “LPCR” account for printing Dial-in access (Unix only) –Sailor:

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 you’re rusty on math, the TA can help in lab

Saving Your Notes First, save the Word file on your M: drive –Connect over the Web to pick it up

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 don’t take for more than 24 hours

Before You Go On a sheet of paper, answer the following (ungraded) question (no names, please): What was the muddiest point in today’s class?