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CMSC 100 Course Overview Professor Marie desJardins mariedj@cs.umbc.edu Thursday, August 28, 2008 Thu 8/28/08 CMSC 100 -- Overview 2 Overview What is Computer Science? Course Logistics First Assignments UPC Example Thu 8/28/08 CMSC 100 -- Overview 3 What is Computer Science? 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 we’re really taking off) 1984: Apple Macintosh 128K (my first computer!!) 2008: MacBook Air (my newest computer!) Thu 8/28/08 CMSC 100 -- Overview 5 Moore’s Law Computer memory (and processing speed, resolution, and just about everything else) increases exponentially (roughly: doubles every 18-24 months) Thu 8/28/08 CMSC 100 -- Overview 6 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) Thu 8/28/08 CMSC 100 -- Overview 7 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! Thu 8/28/08 CMSC 100 -- Overview 8 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 don’t come whining to me about how slow your computer is! Thu 8/28/08 CMSC 100 -- Overview 9 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 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: I’m going to guess around 100. Thu 8/28/08 CMSC 100 -- Overview 10 Grand Challenges for CS Ubiquitous Computing and Information Search Situation Awareness Autonomous Vehicles NIST Human-Level Intelligence DARPA Claytronics http://www.cs.cmu.edu/~claytronics/software/ thebrain.mcgill.ca 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 Thu 8/28/08 CMSC 100 -- Overview 12 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 Thu 8/28/08 CMSC 100 -- Overview 13 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) Thu 8/28/08 CMSC 100 -- Overview 14 Hardware Patterns of bits Memory / storage registers Machine-language instructions Switches and Boolean logic blocks Thu 8/28/08 CMSC 100 -- Overview 15 Systems Operating systems Compilers Thu 8/28/08 CMSC 100 -- Overview 16 Software Programs Programming languages Thu 8/28/08 CMSC 100 -- Overview 17 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 Thu 8/28/08 CMSC 100 -- Overview 18 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 Thu 8/28/08 CMSC 100 -- Overview 19 Course Logistics Instructor: Prof. Marie desJardins, mariedj@cs.umbc.edu http://www.csee.umbc.edu/~mariedj/ Office hours: Mon 11-12, Thurs 3:30-4:30, ITE 337 TA: Ms. Chaitra Sathyanarayana, chaitra1@umbc.edu Office hours: Tues 11-12, Wed 2:30-3:30, ITE 334 Course website/syllabus: http://www.csee.umbc.edu/courses/undergraduate/100/Fall08/ Schedule: http://www.csee.umbc.edu/courses/undergraduate/100/Fall08/schedule.html Thu 8/28/08 CMSC 100 -- Overview 20 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, Hal’s Legacy Thu 8/28/08 CMSC 100 -- Overview 21 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 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 Thu 8/28/08 CMSC 100 -- Overview 22 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 Thu 8/28/08 CMSC 100 -- Overview 23 Academic Honesty Policy See handout… Thu 8/28/08 CMSC 100 -- Overview 24 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(?) Thu 8/28/08 CMSC 100 -- Overview 25 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 Thu 8/28/08 CMSC 100 -- Overview 26 EXAMPLE: Universal Product Codes Slides for the UPC example courtesy of Prof. Michael Littman (Rutgers University) • 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. Thu 8/28/08 CMSC 100 -- Overview 27 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. Thu 8/28/08 CMSC 100 -- Overview 28 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 Thu 8/28/08 CMSC 100 -- Overview 29 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? Thu 8/28/08 CMSC 100 -- Overview 30 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 Thu 8/28/08 CMSC 100 -- Overview 31 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 Thu 8/28/08 CMSC 100 -- Overview 32 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. Thu 8/28/08 CMSC 100 -- Overview 33 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. Thu 8/28/08 CMSC 100 -- Overview 34 Code and Example 01660000070 set evensum to d2+d4+d6+d8+d10 set oddsum to d1+d3+d5+d7+d9+d11 set checkdigit to (0-(3*oddsum+oddsum)) mod 10 01660000070 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 • Lime juice: 01660000070→016600000708 all are two • Franks: 04660000070→046600000705 digits different • Choc Egg: 05660000070→056600000704 now • Salmon: 08660000070→086600000701 Thu 8/28/08 CMSC 100 -- Overview 35 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. Thu 8/28/08 CMSC 100 -- Overview 36 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? Thu 8/28/08 CMSC 100 -- Overview 37 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 (base 10) into a series of bits (base 2). • 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). Thu 8/28/08 CMSC 100 -- Overview 38 Bits Digits are encoded as 7-bit 0: 0001101 5: 0110001 patterns that all: 1: 0011001 6: 0101111 •start with 0, end with 1 2: 0010011 7: 0111011 •switch from 0 to 1 twice •include no reverse 3: 0111101 8: 0110111 complements 4: 0100011 9: 0001011 • Encode d1 d2 d3 d4 d5 d6 d7 d8 d9 d10 d11 d12 as: 101 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 we’re scanning in!) Thu 8/28/08 CMSC 100 -- Overview 39 How Many Bits? • How many bits (zeros and ones) long is the code for the original 12-digit sequence? Thu 8/28/08 CMSC 100 -- Overview 40 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. Thu 8/28/08 CMSC 100 -- Overview 41 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. Thu 8/28/08 CMSC 100 -- Overview 42 Whew! The UPC example illustrates: Abstraction Binary numbers and modulo math Encoding (error correction, readability constraints) Thu 8/28/08 CMSC 100 -- Overview 43

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