CMSC 100
Course Overview
Professor Marie desJardins
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 128K (my first computer!!)
 2008: MacBook 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 (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?)
 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
Tue 9/1/09
that external storage is usually measured in decimal rather than binary (1000 bytes = 1K, and so on)
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!
Tue 9/1/09
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 a 160G hard
drive....
 ...a factor of 1018 more RAM and 1013 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!
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 PowerPoint
What kind of computer you should buy
Advanced programming techniques
Tue 9/1/09
CMSC 100 -- Overview
19
Course Logistics
 Instructor: Prof. Marie desJardins, 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/Fall09/
 Schedule:
http://www.csee.umbc.edu/courses/undergraduate/100/Fall09/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. 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 (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 (110g)
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 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
•
•
•
•
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 0-000000-000000?
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?
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).
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 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!)
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 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 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: 1110010-1011100-1000010-1110010-1110010 (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