1. CMSC 100 Course Overview Adapted from slides provided by Dr. desJardins Robert Holder holder1@umbc.edu holder1@umbc.edu Thursday, September 1, 2011

2. Thu 9/1/2011 CMSC 100 -- Overview 2  What is your name?  What is your major?  What was your first computer you ever used?  What did you use it for?

3. Thu 9/1/2011 CMSC 100 -- Overview 3 Course Logistics  Instructor: Robert Holder, holder1@umbc.eduholder1@umbc.edu  Office hours: Tuesday 11:30-12:30 & By appointment ITE 201F  TA: Debdatta Mukherjee, dmu1@umbc.edudmu1@umbc.edu  Office hours: TBD  Course website/syllabus: http://www.csee.umbc.edu/courses/undergraduate/100/Fall11/ http://www.csee.umbc.edu/courses/undergraduate/100/Fall11/  Schedule: http://www.csee.umbc.edu/courses/undergraduate/100/Fall11/schedule.html http://www.csee.umbc.edu/courses/undergraduate/100/Fall11/schedule.html

4. Thu 9/1/2011 CMSC 100 -- Overview 4 Textbooks  Brookshear, Introduction to Computer Science

5. Thu 9/1/2011 CMSC 100 -- Overview 5 Overview  What is Computer Science?  Course Logistics  First Assignments  UPC Example (if time)

6. What is Computer Science?

7. What is Computer Science? (2)  “Computer science is no more about computers than astronomy is about telescopes.”- Edsger Dijkstra Thu 9/1/2011 CMSC 100 -- Overview 7

8. What is Computer Science? (3)  “Computer science is the study of how computers can make the world a better place.”- Robert Holder Thu 9/1/2011 CMSC 100 -- Overview 8

9. Grand Challenges for CS http:///www.cs.cmu.edu/~claytronics/software thebrain.mcgill.ca Claytronics Human-Level Intelligence Information Search Ubiquitous Computing and Situation Awareness Autonomous Vehicles NIST DARPA

10. Thu 9/1/2011 CMSC 100 -- Overview 10 The Computer Revolution  How fast did this happen?  [ http://www.blinkenlights.com/pc.shtml ]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 we’re really taking off)  1984: Apple Macintosh 128K  2008: MacBook Air

11. Thu 9/1/2011 CMSC 100 -- Overview 11 What Was It Like Then?  The PDP-11/70s my advisor used in college had 64K of RAM, with hard disks that held less than 1M of external storage  “... And I 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!”

12. Thu 9/1/2011 CMSC 100 -- Overview 12 What Is It Like Now?  The PDP-11/70s my advisor used in college had 64K of RAM, with hard disks that held less than 1M of memory  The cheapest laptop at Best Buy has 1G of RAM and a 250G hard drive for $200 ...a factor of 10 18 more RAM and 10 13 more disk space ...and your iPod nano has 8G (or 16G!) of blindingly fast storage  “...so don’t come whining to me about how slow your computer is!”

13. Thu 9/1/2011 CMSC 100 -- Overview 13 Moore’s Law  Computer memory (and processing speed, resolution, and just about everything else) increases exponentially  (roughly: doubles every 18-24 months)

14. Thu 9/1/2011 CMSC 100 -- Overview 14 Measuring Memory  One 0/1 (“no/yes”) “bit” is the basic unit of memory  Eight (2 3 ) bits = one byte  1,024 (2 10 ) bytes = one kilobyte (1K) *  1,024K (2 20 bytes) = one megabyte (1M)  1,024K (2 30 bytes) = one gigabyte (1G)  1,024 (2 40 bytes) = one terabyte (1T)  1,024 (2 50 bytes) = one petabyte (1P) ... 2 80 bytes = one yottabyte (1Y?)  How many different patterns can you represent with one bit of storage?  Two! (It’s either 0 or 1; that’s it, no in between)  How many different patterns can you represent with one byte of storage? * Note that external storage is usually measured in decimal rather than binary (1000 bytes = 1K, and so on)

15. Thu 9/1/2011 CMSC 100 -- Overview 15 It’s Not Just Speed, It’s Quantity  So just how big a revolution are we talking about?  How many computers do you think were in the room when my advisor took her first programming class?  Answer: ZERO(*).  How many computers are in this room? (( * First we need to decide what is a computer… not so easy!) AA nswer: I’m going to guess around 100.

16. Speed AND Quantity Thu 9/1/2011 CMSC 100 -- Overview 16

17. Thu 9/1/2011 CMSC 100 -- Overview 17 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

18. Thu 9/1/2011 CMSC 100 -- Overview 18 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

19. Thu 9/1/2011 CMSC 100 -- Overview 19 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 we’ve 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)

20. Thu 9/1/2011 CMSC 100 -- Overview 20 Hardware  Patterns of bits  Memory / storage registers  Machine-language instructions  Switches and Boolean logic blocks

21. Thu 9/1/2011 CMSC 100 -- Overview 21 Systems  Operating systems  Compilers

22. Thu 9/1/2011 CMSC 100 -- Overview 22 Software  Programs  Programming languages

23. Thu 9/1/2011 CMSC 100 -- Overview 23 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 Scratch)  Foundational mathematics for computer science

24. Thu 9/1/2011 CMSC 100 -- Overview 24 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

25. Thu 9/1/2011 CMSC 100 -- Overview 25 Course Logistics  Instructor: Robert Holder, holder1@umbc.eduholder1@umbc.edu  Office hours: By appointment  TA: Debdatta Mukherjee, dmu1@umbc.edudmu1@umbc.edu  Office hours: TBD  Course website/syllabus: http://www.csee.umbc.edu/courses/undergraduate/100/Fall11/ http://www.csee.umbc.edu/courses/undergraduate/100/Fall11/  Schedule: http://www.csee.umbc.edu/courses/undergraduate/100/Fall11/schedule.html http://www.csee.umbc.edu/courses/undergraduate/100/Fall11/schedule.html

26. Thu 9/1/2011 CMSC 100 -- Overview 26 Textbooks  Brookshear, Introduction to Computer Science

27. Thu 9/1/2011 CMSC 100 -- Overview 27 My Expectations  Students will…  Attend class regularly  Be prompt, and not engage in distracting or disruptive behaviors NO LAPTOPS OR CELLPHONES DURING CLASS (yeah, I know it seems weird in a CS class…)  Take responsibility for knowing what work is due, and turning the coursework in promptly  Follow the course’s academic honesty policy, and not present another’s 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

28. Thu 9/1/2011 CMSC 100 -- Overview 28 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

29. Thu 9/1/2011 CMSC 100 -- Overview 29 Academic Honesty Policy  See handout…

30. Thu 9/1/2011 CMSC 100 -- Overview 30 Course Communications  Email  Requests for extensions, questions about course policies  Instructor  Grading inquiries, requests for help with assignments  TA  Still having trouble? Talk to instructor  Office hours  Posted on website  Blackboard  Instructor postings  Discussion board  Assignment submission

31. Thu 9/1/2011 CMSC 100 -- Overview 31 First Assignments  First Assignments  Academic Honesty Policy and Survey: Due Thursday 9/8  HW 1: Due Tuesday 9/13  Homework expectations:  In general, there will be an assignment (either a written homework or a programming assignment) due each week(at least for the first part of the semester).  These assignments will typically be based on the assigned reading.  The primary purpose of the written assignments is to keep you on track with the reading, and to provide me with feedback about problem areas, well in advance of the midterm and final exams. (The exams will be very similar to the written assignments.)  Please plan your time (to do the reading and complete the assignments) accordingly!  All assignments are to be submitted in class (i.e., as hardcopy!) unless otherwise specified  Late policy (see course syllabus)

32. Thu 9/1/2011 CMSC 100 -- Overview 32 EXAMPLE: Universal Product Codes First scanned product: Wrigley’s 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)

33. Thu 9/1/2011 CMSC 100 -- Overview 33 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.

34. Thu 9/1/2011 CMSC 100 -- Overview 34 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

35. Thu 9/1/2011 CMSC 100 -- Overview 35 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?

36. Thu 9/1/2011 CMSC 100 -- Overview 36 Encode Name By 11 Digits First 6 digits: Manufacturer First digit, product category: 0, 1, 6, 7, 8, or 9: most products 2: store’s use, for variable-weight items 3: drugs by National Drug Code number Last 5 digits: Manufacturer-assigned ID

37. Thu 9/1/2011 CMSC 100 -- Overview 37 Examples Labels: 0-72782-051440 0=general product 72782= Avery 051440=Avery’s code for this product Ponds: 3-05210-04300 3=drug code 05210= Unilever 04300=National Drug Code for this product

38. Thu 9/1/2011 CMSC 100 -- Overview 38 12-Digit Number The UPC folks decided to include another digit for error checking. Example: 01660000070 Rose’s 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.

39. Thu 9/1/2011 CMSC 100 -- Overview 39 Check Digit 1. Add the digits in the odd-numbered positions (first, third, fifth, etc.) together and multiply by three. 2. Add the digits in the even-numbered positions (second, fourth, sixth, etc.) to the result. 3. Subtract the result from the next-higher multiple of ten. The result is the check digit.

40. Thu 9/1/2011 CMSC 100 -- Overview 40 Code and Example Lime juice: 01660000070→016600000708 Franks: 04660000070→046600000705 Choc Egg: 05660000070→056600000704 Salmon: 08660000070→086600000701 set evensum to d2+d4+d6+d8+d10 set oddsum to d1+d3+d5+d7+d9+d11 set checkdigit to 10 - (3*oddsum+oddsum) mod 10 01660000070 0166000007001660000070 odd-digit sum: 0+6+0+0+0+0=6 even-digit sum: 1+6+0+0+7=14 odd*3+even = 6*3+14=32 subtract from mult of 10=40-32=8 all are two digits different now

41. Thu 9/1/2011 CMSC 100 -- Overview 41 Some (Mod) Math 3 x S odd + S even = 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.

42. Thu 9/1/2011 CMSC 100 -- Overview 42 More Modulo Math What’s 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? Reminder: Check digit = 10 – (3*oddsum + evensum) mod 10

43. Thu 9/1/2011 CMSC 100 -- Overview 43 Bits We’ve 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 into a series of bits. Also, we want to be sure we alternate 0s and 1s often enough (e.g., don’t 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 we’re reading it in).

44. Thu 9/1/2011 CMSC 100 -- Overview 44 Bits Encode d 1 d 2 d 3 d 4 d 5 d 6 d 7 d 8 d 9 d 10 d 11 d 12 as: 101 d 1 d 2 d 3 d 4 d 5 d 6 01010 d 7 d 8 d 9 d 10 d 11 d 12 101 Last 6 digits have 0s and 1s flipped. (No reverse complements  can tell what direction we’re scanning in!) Digits are encoded as 7-bit patterns that all: start with 0, end with 1 switch from 0 to 1 twice include no reverse complements 0: 0001101 1: 0011001 2: 0010011 3: 0111101 4: 0100011 5: 0110001 6: 0101111 7: 0111011 8: 0110111 9: 0001011

45. Thu 9/1/2011 CMSC 100 -- Overview 45 How Many Bits? How many bits (zeros and ones) long is the code for the original 12-digit sequence?

46. Thu 9/1/2011 CMSC 100 -- Overview 46 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.

47. Thu 9/1/2011 CMSC 100 -- Overview 47 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. 0: 0001101 1: 0011001 2: 0010011 3: 0111101 4: 0100011 5: 0110001 6: 0101111 7: 0111011 8: 0110111 9: 0001011

48. Thu 9/1/2011 CMSC 100 -- Overview 48 Whew!  The UPC example illustrates:  Abstraction  Binary numbers and modulo math  Encoding (error correction, readability constraints)