CMSC 100 Course Overview

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CMSC 100Course Overview

• Professor Marie desJardinsmariedj_at_cs.umbc.eduThu
  rsday, August 28, 2008

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Welcome!
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Overview

• What is Computer Science?
• Course Logistics
• First Assignments
• UPC Example

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What is Computer Science?
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The Computer Revolution

• How fast did this happen?
• http//www.blinkenlights.com/pc.shtml
• 1950 Simon (plans published in Radio
  Electronics)
• 1973 HP 65 (programmable calculator)
• 1975 Altair 8800 (first widely used programmable
  computer kit)
• 1977 Apple II (a huge breakthrough, the first
  mass-produced, inexpensive personal computer)
• 1981 IBM 5150 PC (now were really taking off)
• 1984 Apple Macintosh 128K (my first computer!!)
• 2008 MacBook Air(my newest computer!)

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Moores Law

• Computer memory (and processing speed,
  resolution, and just about everything else)
  increases exponentially
• (roughly doubles every 18-24 months)

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Measuring Memory

• One yes/no bit is the basic unit of memory
• Eight (23) bits one byte
• 1,024 (210) bytes one kilobyte (1K)
• 1,024K (220 bytes) one megabyte (1M)
• 1,024K (230 bytes) one gigabyte (1G)
• 1,024 (240 bytes) one terabyte (1T)
• 1,024 (250 bytes) one petabyte (1P)
• ... 280 bytes one yottabyte (1Y?)

Note that external storage is usually measured
in decimal rather than binary (1000 bytes 1K,
and so on)
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What Was It Like Then?

• The PDP-11/70s we used in college had 64K of RAM,
  with hard disks that held less than 1M of
  external storage
• ... and we had to walk five miles, uphill, in the
  snow, every day! And we had to live in a
  cardboard box in the middle of the road!

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What Is It Like Now?

• The PDP-11/70s we used in college had 64K of RAM,
  with hard disks that held less than 1M of memory
• The cheapest Dell Inspiron laptop has 2G of RAM
  and up to 80G of hard drive storage....
• ...a factor of 1018 more RAM and 1012 more disk
  space
• ...and your iPod nano has 8G of blindingly fast
  storage
• ...so dont come whining to me about how slow
  your computer is!

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Its Not Just Speed, Its Quantity

• So just how big a revolution are we talking
  about?
• How many computers do you think were in the room
  when I took my first programming class?
• Answer ZERO().
• How many computers are in this room?

• ( First we need to decide what is a computer
  not so easy!)
• Answer Im going to guess around 100.

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Grand Challenges for CS
Ubiquitous Computing and Situation Awareness
Information Search
Autonomous Vehicles
NIST
Human-Level Intelligence
DARPA
Claytronics
http//www.cs.cmu.edu/claytronics/software/
thebrain.mcgill.ca
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How Does a Computer Work?

• The work performed by the computer is specified
  by a program, which is written in a programming
  language. This language is converted to sequences
  of machine-language instructions by interpreters
  or compilers, via a predefined set of subroutines
  called the operating system. The instructions,
  which are stored in the memory of the computer,
  define the operations to be performed on data,
  which are also stored in the computer's memory. A
  finite-state machine fetches and executes these
  instructions. The instructions as well as the
  data are represented by patterns of bits. Both
  the finite-state machine and the memory are built
  of storage registers and Boolean logic blocks,
  and the latter are based on simple logical
  functions, such as And, Or, and Invert. These
  logical functions are implemented by switches,
  which are set up either in series or in parallel,
  and these switches control a physical substance,
  such as water or electricity, which is used to
  send one of two possible signals from one switch
  to another 1 or 0. This is the hierarchy of
  abstraction that makes computers work. -- W.
  Daniel Hillis, The Pattern on the Stone

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How Does a Computer Work?

• The work performed by the computer is specified
  by a program, which is written in a programming
  language. This language is converted to sequences
  of machine-language instructions by interpreters
  or compilers, via a predefined set of subroutines
  called the operating system. The instructions,
  which are stored in the memory of the computer,
  define the operations to be performed on data,
  which are also stored in the computer's memory. A
  finite-state machine fetches and executes these
  instructions. The instructions as well as the
  data are represented by patterns of bits. Both
  the finite-state machine and the memory are built
  of storage registers and Boolean logic blocks,
  and the latter are based on simple logical
  functions, such as And, Or, and Invert. These
  logical functions are implemented by switches,
  which are set up either in series or in parallel,
  and these switches control a physical substance,
  such as water or electricity, which is used to
  send one of two possible signals from one switch
  to another 1 or 0. This is the hierarchy of
  abstraction that makes computers work. -- W.
  Daniel Hillis, The Pattern on the Stone

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Abstraction The Key Idea!

• Computers are very complex
• Most interesting programs are very complex
• What makes it possible to design and maintain
  these complex systems??
• Which just means
• Once weve solved a low-level detail, we can
  treat that solution as a black box with known
  inputs and outputs, and not worry about how it
  works.
• The way we get there is called problem reduction
  (or decomposition or divide-and-conquer)

Abstraction!
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Hardware

• Patterns of bits
• Memory / storage registers
• Machine-language instructions
• Switches and Boolean logic blocks

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Systems

• Operating systems
• Compilers

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Software

• Programs
• Programming languages

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What this class is about

• How computers are built, programmed, and used to
  solve problems
• Hardware Digital logic and system architecture
• Systems Operating systems and networks
• Software Basic programming/algorithms,
  databases
• Theory Algorithms, computation, complexity
• Applications AI, graphics,
• Social issues Ethics, privacy, environmental
  impact
• Other skills emphasized
• Effective writing and presentation skills
• Basic programming (in Alice)
• Foundational mathematics for computer science

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What this class is NOT about

• How to install Windows or Linux
• How to use Excel and PowerPoint
• What kind of computer you should buy
• Advanced programming techniques

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Course Logistics

• Instructor Prof. Marie desJardins,
  mariedj_at_cs.umbc.edu http//www.csee.umbc.edu/mari
  edj/Office hours Mon 11-12, Thurs 330-430,
  ITE 337
• TA Ms. Chaitra Sathyanarayana,
  chaitra1_at_umbc.eduOffice hours Tues 11-12, Wed
  230-330, ITE 334
• Course website/syllabus http//www.csee.umbc.edu/
  courses/undergraduate/100/Fall08/
• Schedule http//www.csee.umbc.edu/courses/undergr
  aduate/100/Fall08/schedule.html

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Textbooks

• Brookshear, Introduction to
  Computer Science
• Hillis, The Pattern on the Stone
• Dann et al., Learning to Program with Alice
  (regular or brief edition)
• 100H only Stork, Hals Legacy

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My Expectations

• Students will
• Attend class regularly
• Be prompt, and not engage in distracting or
  disruptive behaviors
• NO LAPTOPS OR CELLPHONES DURING CLASS
• Take responsibility for knowing what work is due,
  and turning the coursework in promptly
• Follow the courses academic honesty policy, and
  not present anothers work as your own
• Be engaged in the learning process, respectful of
  the course staff, and supportive of your fellow
  students
• Express concerns and ask questions
• Understand that the course staff has other
  obligations outside of this class

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Your Expectations

• The instructor will
• Tell students what is expected in terms of
  coursework and behavior
• Be fair in giving assignments, grading
  assignments, and returning coursework in a timely
  fashion
• Answer questions and concerns promptly
• Be open to feedback and suggestions
• Be respectful of students
• Try to make the course useful, interesting, and
  enjoyable
• Understand that students have other obligations
  outside of this class

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Academic Honesty Policy

• See handout

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Course Communications

• Email
• Requests for extensions, questions about course
  policies ? Prof. dJ
• Grading inquiries, requests for help with
  assignments ? TA
• Still having trouble? Talk to Prof. dJ
• Office hours
• One point of EXTRA CREDIT if you come to my
  office hours before 9/12 to introduce yourself!
• Blackboard
• Instructor postings
• Discussion board
• Assignment submission
• Wiki/blog(?)

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First Assignments

• First Assignments
• Academic Honesty Policy and Survey
• Due Tuesday 9/2
• Submit in class
• HW 1
• Due Tuesday 9/9 NOTE CHANGE!
• Submit via Blackboard
• Late policy

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EXAMPLE Universal Product Codes

• First scanned product Wrigleys gum (1974).
• Method of identifying products at point of sale
  by 11-digit numbers.
• Method of encoding digit sequences so they can be
  read quickly and easily by machine.

Slides for the UPC example courtesy of Prof.
Michael Littman (Rutgers University)
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Reduction Idea

• Each level uses an encoding to translate to the
  next level (i.e., the next higher abstraction)
• Patterns of ink.
• Sequence of 95 zeros and ones (bits).
• Sequence of 12 digits.
• Sequence of 11 digits.
• Name/type/manufacturer of product.

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Product Name

• Ponds Dry Skin Cream
• 3.9 oz (110g)
• Unilever Home and Personal Care USA
• Name Badge Labels (Size 2 3/16" x 3 3/8")
• 100 Labels
• Avery Dennison/Avery Division

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11-Digit Number

• Digit 0,1,2,3,4,5,6,7,8,9
• Sequence of 11 digits
• QUESTION How many different items can be
  encoded?

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Encode Name By 11 Digits

• First 6 digits Manufacturer
• First digit, product category
• 0, 1, 6, 7, 8, or 9 most products
• 2 stores use, for variable-weight items
• 3 drugs by National Drug Code number
• Last 5 digits Manufacturer-assigned ID

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Examples

• Labels 0-72782-051440
• 0general product
• 72782 Avery
• 051440Averys code for this product
• Ponds 3-05210-04300
• 3drug code
• 05210 Unilever
• 04300National Drug Code for this product

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12-Digit Number

• The UPC folks decided to include another digit
  for error checking. Example
• 01660000070 Roses Lime Juice (12 oz)
• 04660000070 Eckrich Franks, Jumbo (16 oz)
• 05660000070 Reese PB/Choc Egg (34 g)
• 08660000070 Bumble Bee Salmon (14.75 OZ)
• Misread digit 2 and you turn sweet to sour.

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Check Digit

• Add the digits in the odd-numbered positions
  (first, third, fifth, etc.) together and multiply
  by three.
• Add the digits in the even-numbered positions
  (second, fourth, sixth, etc.) to the result.
• Subtract the result from the next-higher multiple
  of ten. The result is the check digit.

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Code and Example
01660000070
set evensum to d2d4d6d8d10 set oddsum to
d1d3d5d7d9d11 set checkdigit to
(0-(3oddsumoddsum)) mod 10
01660000070
odd-digit sum 0600006 even-digit sum
1600714 odd3even 631432 subtract from
mult of 1040-328

• Lime juice 01660000070?016600000708
• Franks 04660000070?046600000705
• Choc Egg 05660000070?056600000704
• Salmon 08660000070?086600000701

all are two digits different now
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Some (Mod) Math

• 3 x Sodd Seven 0 mod 10
• The sum of the odd-position digits (times 3) plus
  the sum of the even position digits (including
  the check digit) is 0 mod 10.
• Modulo math is just like regular math, except
  things wrap around (like an odometer). Mod 10
  means we only pay attention to the last digit in
  the number.
• Divide by 10 and only keep the remainder.

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More Modulo Math

• Whats the check digit for the code
  0-000000-000000?
• What happens to the check digit if you add one to
  an odd-position digit?
• What happens to the check digit if you add one to
  an even-position digit?

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Bits

• Weve gone from a product name to an 11-digit
  number to a 12-digit number.
• A 0 will appear in the UPC as a white bar (space)
  and a 1 as a black bar.
• So we need to turn each digit (base 10) into a
  series of bits (base 2).
• Also, we want to be sure we alternate 0s and 1s
  often enough (e.g., dont want 20 black bars (1s)
  in a row).
• Finally, we want to have a code that we can scan
  in either direction (i.e., we need to be able to
  tell which direction were reading it in).

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Bits
5 0110001 6 0101111 7 0111011 8 0110111 9
0001011

• Encode d1 d2 d3 d4 d5 d6 d7 d8 d9 d10 d11 d12
  as101 d1 d2 d3 d4 d5 d6 01010 d7 d8 d9 d10 d11
  d12 101

Last 6 digits have 0s and 1s reversed. (No
reverse complements ? can tell what direction
were scanning in!)
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How Many Bits?

• How many bits (zeros and ones) long is the code
  for the original 12-digit sequence?

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Finally, Ink!

• Given the long pattern of bits, we write a 1 as a
  bar and a zero as a space.
• Two 1s in a row become a double-wide bar.
• Two 0s in a row become a double-wide space.
• No UPC has more than four 0s or 1s in a row.
• All digits have equal width.
• All UPCs start and end with bars (actually with
  black-white-black pattern).
• UPCs can be read upside down.
• UPCs can be read at an angle or variable speed
  via ratios.

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Example .......

• Barcode for skin cream
• 3-05210-04300-8 (8 is the check digit)
• start 101 3 0111101
• 05210 0001101-0110001-0010011-0011001-0001101
• middle 01010
• 04300 1110010-1011100-1000010-1110010-1110010
  (rev)
• 8 1001000 (rev) end 101
• The digits underneath are for our benefit.

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Whew!

• The UPC example illustrates
• Abstraction
• Binary numbers and modulo math
• Encoding (error correction, readability
  constraints)