CMSC 100 Course Overview Professor Marie des Jardins

CMSC 100 Course Overview Professor Marie des. Jardins mariedj@cs. umbc. edu Tuesday, September 1, 2009

Tue 9/1/09 CMSC 100 -- Overview 2

Overview ¨What is Computer Science? ¨Course Logistics ¨First Assignments ¨UPC Example (if time) Tue 9/1/09 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 128 K (my first computer!!) · 2008: Mac. Book Air (my newest computer!) Tue 9/1/09 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) Tue 9/1/09 CMSC 100 -- Overview 6

Measuring Memory ¨ One 0/1 (“no/yes”) “bit” is the basic unit of memory · · · · Eight (23) bits = one byte 1, 024 (210) bytes = one kilobyte (1 K)* 1, 024 K (220 bytes) = one megabyte (1 M) 1, 024 K (230 bytes) = one gigabyte (1 G) 1, 024 (240 bytes) = one terabyte (1 T) 1, 024 (250 bytes) = one petabyte (1 P). . . 280 bytes = one yottabyte (1 Y? ) ¨ 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? * Tue 9/1/09 Note that external storage is usually measured in decimal rather than binary (1000 bytes = 1 K, and so on) CMSC 100 -- Overview 7

What Was It Like Then? ¨ The PDP-11/70 s we used in college had 64 K of RAM, with hard disks that held less than 1 M 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! Tue 9/1/09 CMSC 100 -- Overview 8

What Is It Like Now? ¨ The PDP-11/70 s we used in college had 64 K of RAM, with hard disks that held less than 1 M of memory ¨ The cheapest Dell Inspiron laptop has 2 G of RAM and a 160 G hard drive. . ¨. . . a factor of 1018 more RAM and 1013 more disk space ¨. . . and your i. Pod nano has 8 G (or 16 G!) of blindingly fast storage ¨. . . so don’t come whining to me about how slow your computer is! Tue 9/1/09 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. Tue 9/1/09 CMSC 100 -- Overview 10

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

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 Tue 9/1/09 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 Tue 9/1/09 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) Tue 9/1/09 CMSC 100 -- Overview 14

Hardware ¨ ¨ Patterns of bits Memory / storage registers Machine-language instructions Switches and Boolean logic blocks Tue 9/1/09 CMSC 100 -- Overview 15

Systems ¨ Operating systems ¨ Compilers Tue 9/1/09 CMSC 100 -- Overview 16

Software ¨ Programs ¨ Programming languages Tue 9/1/09 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 Tue 9/1/09 CMSC 100 -- Overview 18

What this class is NOT about ¨ ¨ How to install Windows or Linux How to use Excel and Power. Point What kind of computer you should buy Advanced programming techniques Tue 9/1/09 CMSC 100 -- Overview 19

Course Logistics ¨ Instructor: Prof. Marie des. Jardins, mariedj@cs. umbc. edu http: //www. csee. umbc. edu/~mariedj/ Office hours: Tues 10 -11, Thurs 3: 30 -4: 30, ITE 337 ¨ TA: TBA ¨ Course website/syllabus: http: //www. csee. umbc. edu/courses/undergraduate/100/Fall 09/ ¨ Schedule: http: //www. csee. umbc. edu/courses/undergraduate/100/Fall 09/schedule. html Tue 9/1/09 CMSC 100 -- Overview 20

Textbooks ¨ Brookshear, Introduction to Computer Science ¨ Dann et al. , Learning to Program with Alice (regular or brief edition) Tue 9/1/09 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 �(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 Tue 9/1/09 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 Tue 9/1/09 CMSC 100 -- Overview 23

Academic Honesty Policy ¨ See handout… Tue 9/1/09 CMSC 100 -- Overview 24

Course Communications ¨ Email · Requests for extensions, questions about course policies Prof. d. J · Grading inquiries, requests for help with assignments TA � Still having trouble? Talk to Prof. d. J ¨ Office hours · One point of EXTRA CREDIT if you come to my office hours (or stop by any time my door is open) by 9/18 to introduce yourself and chat for a few minutes! ¨ Blackboard · · Tue 9/1/09 Instructor postings Discussion board Assignment submission Wiki/blog(? ) CMSC 100 -- Overview 25

First Assignments ¨ First Assignments · Academic Honesty Policy and Survey: Due Thursday 9/3 · HW 1: Due Thursday 9/10 ¨ Homework expectations: · In general, there will be an assignment (either a written homework or a programming assignment) due each Thursday (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) Tue 9/1/09 CMSC 100 -- Overview 26

EXAMPLE: Universal Product Codes Slides for the UPC example courtesy of Prof. Michael Littman (Rutgers University) • • • Tue 9/1/09 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. CMSC 100 -- Overview 27

Reduction Idea • Each level uses an encoding to translate to the next level (i. e. , the next higher abstraction) • • • Tue 9/1/09 Patterns of ink. Sequence of 95 zeros and ones (“bits”). Sequence of 12 digits. Sequence of 11 digits. Name/type/manufacturer of product. CMSC 100 -- Overview 28

Product Name • Ponds Dry Skin Cream • • • Name Badge Labels (Size 2 3/16" x 3 3/8") • • Tue 9/1/09 3. 9 oz (110 g) Unilever Home and Personal Care USA 100 Labels Avery Dennison/Avery Division CMSC 100 -- Overview 29

11 -Digit Number • • • Tue 9/1/09 Digit = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9} Sequence of 11 digits QUESTION: How many different items can be encoded? CMSC 100 -- Overview 30

Encode Name By 11 Digits • First 6 digits: Manufacturer • • Tue 9/1/09 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 CMSC 100 -- Overview 31

Examples • Labels: 0 -72782 -051440 • • Ponds: 3 -05210 -04300 • • • Tue 9/1/09 0=general product 72782= Avery 051440=Avery’s code for this product 3=drug code 05210= Unilever 04300=National Drug Code for this product CMSC 100 -- Overview 32

12 -Digit Number • The UPC folks decided to include another digit for error checking. Example: • • • Tue 9/1/09 01660000070 04660000070 05660000070 08660000070 Rose’s Lime Juice (12 oz) Eckrich Franks, Jumbo (16 oz) Reese PB/Choc Egg (34 g) Bumble Bee Salmon (14. 75 OZ) Misread digit #2 and you turn sweet to sour. 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. Tue 9/1/09 CMSC 100 -- Overview 34

Code and Example 01660000070 set evensum to d 2+d 4+d 6+d 8+d 10 set oddsum to d 1+d 3+d 5+d 7+d 9+d 11 set checkdigit to (0 -(3*oddsum+oddsum)) mod 10 01660000070 odd-digit sum: 0+6+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 • • Tue 9/1/09 Lime juice: 01660000070→ 016600000708 Franks: 04660000070→ 046600000705 Choc Egg: 05660000070→ 056600000704 Salmon: 08660000070→ 086600000701 CMSC 100 -- Overview all are two digits different now 35

Some (Mod) Math • • Tue 9/1/09 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. CMSC 100 -- Overview 36

More Modulo Math • • • Tue 9/1/09 What’s the check digit for the code 0 -000000? What happens to the check digit if you add one to an oddposition digit? What happens to the check digit if you add one to an even-position digit? 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 0 s and 1 s often enough (e. g. , don’t want 20 black bars (1 s) 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). Tue 9/1/09 CMSC 100 -- Overview 38

Bits 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 • 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 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 0 s and 1 s reversed. (No reverse complements can tell what direction we’re scanning in!) Tue 9/1/09 CMSC 100 -- Overview 39

How Many Bits? • Tue 9/1/09 How many bits (zeros and ones) long is the code for the original 12 -digit sequence? CMSC 100 -- Overview 40

Finally, Ink! • • Tue 9/1/09 Given the long pattern of bits, we write a 1 as a bar and a zero as a space. Two 1 s in a row become a double-wide bar. Two 0 s in a row become a double-wide space. No UPC has more than four 0 s or 1 s in a row. All digits have equal width. All UPCs start and end with bars (actually with blackwhite-black pattern). UPCs can be read upside down. UPCs can be read at an angle or variable speed via ratios. CMSC 100 -- Overview 41

Example Tue 9/1/09 . . . . • • 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 (rev) 8: 1001000 (rev); end: 101 • The digits underneath are for our benefit. CMSC 100 -- Overview 42

Whew! ¨ The UPC example illustrates: · Abstraction · Binary numbers and modulo math · Encoding (error correction, readability constraints) Tue 9/1/09 CMSC 100 -- Overview 43