CS 111 – Aug. 25
• What is this class about?
– IT = How to make computers useful for people
– Understanding what goes on inside (and outside) the
machine
• Commitment
– For next day, please read Chapter 0
CS versus IT
• Computer science
–
–
–
–
–
How do we solve problems?
Classify problems; insight from solutions
How to represent information, languages
What is knowledge/information?
How to design better computing system
• Information Technology
– An applied science
– Practical goals: make money, win wars, security,
safety, protect environment, etc.
– How can we use the computer to accomplish ….?
Human history
• Agricultural age (up to ~ 1800)
• Industrial age (1800 – 1950)
• Information age (1950 --)
– We live in an information-based society. In other
words, many tasks are defined in terms of doing
something with information.
– People and businesses depend on IT to get things
done.
– Not all countries follow this timeline.
IT functions
What does IT need to do?
• Input or capture information
• Store information for future use
• Process: manipulate information and present it
in a meaningful form
• Output, i.e. allow retrieval of info
• Communicate / transmit info to another location
IT components
• Computer: an electronic device that can
process and store information
• Communication network
• Know-how: the skills needed to make best use
of the computer system
• Goals throughout IT:
– Speed
– Consistency and reliability
– Precision
Business components
What does a business need to do?
• Create something, i.e. manufacturing or service
• Sell it
• Ship it
• Keep track of employees, customers, inventory
• Communicate and coordinate all these activities.
• IT speeds up the process, reduces error/waste.
• Example: think of an airline.
CS 111 – Aug. 26
Review:
• How might an airline use IT?
• Chapter 0
– Computer origins
– Algorithms
– Abstraction
• Commitment for next day:
– Please read section 1.1
History
• Analog machines
– Abacus
– Mechanical calculators, adding machines, cash
registers
– Babbage suggested a programmable machine
– Hollerith adapted Jacquard’s punch cards
• Digital machines
– ENIAC, ABC, Mark I, Colossus
– Became commercially successful in 1950s
– Became increasingly affordable by 1980s
• Innovations often respond to needs
HW & SW
• Hardware – physical computer components
– CPU, memory, I/O devices, network
• Software – programs that run on machine
– Allows computer to do useful work (or play)
– Tell the computer exactly what to do
– Behind any program is its algorithm
• The secret to how it really works
• Clearly defined list of steps to solve a problem
• Needs to be precise, and spell out details
• Analogy:
– a restaurant building, versus the actual restaurant
Algorithm example
• Euclidean algorithm: Given two numbers, find
their greatest common divisor….
1. Let m = larger, and n = smaller number
2. Let r = remainder after dividing m/n
3. If r = 0, then our answer is n, and we’re done.
But if r ≠ 0, let m = n, and let n = r, and go to step 2.
• Try it out…Do you understand the steps? Does
the procedure work?
• BTW, an algorithm should also clearly specify its
input and output. √
Abstraction
• Our way to manage complex problems
• Big picture first, then the details
– Details omitted until they become important
– “top-down” design
– Ex. Road map
• We can study a machine without knowing how to
build one
Bits
Preview of section 1.1:
• All information in computer is in binary form (0/1)
• Smallest unit of information is the bit: a single 0
or 1
• When we have lots of bits, usually grouped in
set of 8 called a byte
• Basic building block of CPU is the logic gate,
which manipulates bit values.
– Very fast
– Logic gates combine to perform math operations
CS 111 – Aug. 27
• Section 1.1
–
–
–
–
Binary data and operations
Logic gates
Flip-flop
A binary shorthand: hexadecimal
• Commitment for next day:
– Please read sections 1.2 and 1.3
Binary
• All information inside computer is in binary
• Smallest unit of data is the bit
• Only the values 0 and 1 are used
0 means “false” or “off” or the number 0
1 means “true” or “on” or the number 1
• Individual bit values can be manipulated with
Boolean operations: “and”, “or”, “not”, etc.
– In hardware, we implement these operations with
logic gates.
Boolean examples
• AND
– To graduate, you must have 128 credits and 2.0 GPA.
• OR
– Classics scholarship requires 3 years of Latin or 3 years of
Greek.
• XOR (“exclusive” or)
– To go to Cincinnati, you can fly or drive. In other words, it
doesn’t make sense to do both.
– Do you want a 2-door or a 4-door car?
• NOT
– If a statement is true, its negation is false, and vice versa.
Gates
• Basic building blocks of
CPU’s circuitry.
• Usually 2 inputs.
• X and Y could be 0 or 1.
• Combining gates into a
circuit:
– The output of one gate
becomes input to another.
– This is how more useful
operations are performed.
‘AND’ and ‘OR’
AND
OR
X
Y
ans
X
Y
ans
1
1
1
1
1
1
1
0
0
1
0
1
0
1
0
0
1
1
0
0
0
0
0
0
Note:
0 AND (anything) = 0
1 OR (anything) = 1
XOR
• XOR basically says,
“either but not both”
• The output is 1 if both
inputs are different.
XOR
X
Y
Ans
1
1
0
1
0
1
0
1
1
0
0
0
NOR, NAND
• NOR gate
– Negation of the OR
– Same as feeding output of OR into a NOT gate.
– Symbol for NOR gate is same as OR but with a
loop on the end.
• NAND gate
– Negation of the AND…. analogous to NOR.
• Interesting property:
– NOR and NAND are universal gates. Any other
boolean operation can be implemented by using
several NAND’s or several NOR’s.
Flip-flop circuit
• Circuit that can “store” or remember a 1 bit value.
• Its own output is used as input to one of its gates.
• To change flip-flop’s value, set one of the inputs
to 1.
• See diagrams on page 23.
Hexadecimal
• One bit is not enough to convey much
information. A single word or numerical value
requires several bits.
– Ex. The word “cat” can be represented by this bit
sequence: 011000110110000101110011
• “Hex” is a shorthand for binary
– Allows us to represent every 4 bits with just 1 symbol.
– Ex. 24 bits of information= 6 hex characters.
– The word hexadecimal means there are 16 possible
symbols, so we use 0-9 and then a-f.
• See table on page 25.
CS 111 – Aug. 30
• 1.2 – 1.3
– Information arranged in memory
– Types of memory
– Disk properties
• Commitment for next day:
– Read pp. 38-40, 45-47. In other words, only the parts
of 1.4 and 1.5 dealing with numbers and text
Memory units
• Bit = a single 0 or 1 value
• Nibble = 4 bits = 1 hexadecimal digit
• Byte = 8 bits
•
•
•
•
Kilobyte (KB) = 210 bytes
Megabyte (MB) = 220 bytes
Gigabyte (GB) = 230 bytes
Terabyte (TB) = 240 bytes
• 210 = 1024, though 1000 is a close approx.
CPU and memory
• CPU’s job is to obey instructions and do calculations
• Memory system stores information for current and future
use
– CPU has tiny number of “registers” for calculations
– main memory (RAM) stores all files currently open
– Secondary memory (e.g. hard drive) is for long-term
storage of files
– Backup system: tape, external hard drive
• Other types of memory:
– Cache, between CPU and RAM
– Removable drive, e.g. USB or DVD
RAM
• Runs on electricity: volatile but fast
• Each byte is numbered and addressable
– Capable of holding a single character or small #
Address
Contents
0
“c”
1
“a”
2
“t”
3
9
4
25
5
100
…
…
Memory comparison
Type
Size
Access time
Cost per MB
CPU registers
256 bytes
1 ns
N/A
Cache
64 KB
2 ns
$ 20
RAM
512 MB
50 ns
$ 0.20
Disk
200 GB
100,000 ns
$ 0.0002
Numbers are approximate.
“ns” means nanosecond = 1 billionth of a second
Disk geometry
• Tracks
• Sectors
• Platters
• Hard drive 
• Ex. A DVD has roughly 50,000 tracks
and 40 (2KB) sectors per track.
Disk access time
Analogous to a record player:
• Seek time: read-write head moves to find the
correct track (up to ~ 8ms)
• Latency: wait for disk to rotate to beginning of
file (up to ~ 4ms)
• Transfer: grab info from disk (e.g. 1 MB/sec
read or 0.1 MB/sec write)
CS 111 – Sept. 1
Intro to data representation
• Binary numbers
– Convert binary  decimal
– Convert decimal  binary
• Text
– ASCII and Unicode
• Commitment:
– For lab: Be sure you understand number conversions
– For Friday: Please finish reading sections 1.4 and 1.5
Numbers in binary
• Place value system just like decimal
– We understand 278 = (2 * 100) + (7 * 10) + (8 * 1)
• In a binary number:
– Each digit is either a 0 or 1
– Digits are multiplied by powers of 2, not powers of 10.
• For example, 001110 and 100011:
32 *
16 *
8*
4*
2*
1*
Value
0
0
1
1
1
0
14
1
0
0
0
1
1
35
Powers of 2
•
•
•
•
•
20 = 1
21 = 2
22 = 4
23 = 8
24 = 16
…
• 210 ~ 1 thousand
• 220 ~ 1 million
• 230 ~ 1 billion
• Let’s say we have 4 bits.
– What is the lowest # ?
– What is the highest # ?
• What if we had 5 bits?
• Is there a pattern?
Decimal  binary
• One thing to note is that binary numbers are
“longer” than decimal.
– A 5-digit decimal number may turn out to be 15 bits
long.
• My technique is the “binary store”
–
–
–
–
All merchandise is priced $1, $2, $4, $8, $16, …
You enter store with some money, say $45.
Goal is to always buy most expensive gift possible.
So, 45 = 32 + 8 + 4 + 1
32 *
16 *
8*
4*
2*
1*
1
0
1
1
0
1
Another example
• Convert 61 to binary:
• Go to binary store with $61…
61 = 32 + 16 + 8 + 4 + 1
Another way to write this is:
61 = 25 + 24 + 23 + 22 + 20
• Our binary answer is 111101.
CS 111 – Sept. 3
More data representation
• Review hex notation
• Text
– ASCII and Unicode
• Sound and images
• Commitment:
– For Wednesday: Please read pp. 46-57
– Quiz next Friday
Numbers in a byte
• A byte is 8 bits
• So, how big can an 8-bit binary number be?
• Hexidecimal shorthand
– 8/4 = 2 hexidecimal digits per byte
– What do the letters ‘a’ – ‘f’ mean?
a = 10, b = 11, c = 12, d = 13, e = 14, f = 15
– Example: 010111102 = 5e in hex.
– Try this one: 1110002 = ______ in hex.
– Try this one: a4c in hex = ________ in binary.
Text
• Fundamental unit is the character.
• Each character of a text document is given a
numerical code.
• ASCII code
– Contiguous (make it easy to alphabetize)
– Case sensitive
– One byte per character
• ASCII table (p. 597)
– ‘A’ = 65
‘a’ = 97
‘0’ = 48
– Try encoding the word: “Dog”
Unicode
• To support foreign alphabet and misc. symbols.
• Extension of ASCII
• 16 bits per character, rather than 8
• unicode.org has code charts
• Codes are given in hex.
Sampling
• “Real” sound and visual data are continuous, constantly
changing
• Sampling means to take rapid snapshots
• Video: 30 images a second is good enough for our eyes
• Real sound is in the form of a wave (p. 43)
• Sampling sound means finding points along the curve.
– Music CD: take a reading 44,100 times a second, and store as a
16-bit number… How much data is captured in 1 hour?
– MIDI (= Musical Instrument Digital Interface) uses far less space,
though does not sound like an actual recording.
Images
• Fundamental unit is the pixel
• Usually 8 bits (1 byte) per pixel
– This means each pixel is assigned a value from 0 to
255
– What do these numbers mean? Depends on color
system
– Grayscale = system for B/W images
• Image dimensions are (horiz x vert)
– Ex. 400 x 300  120,000 pixels
• Aspect ratio
– When changing size, this should not change.
Resolution
• Resolution – total number of pixels in image
– “hi res” takes up more space
– “lo res” means pixels become more obvious, pixelated
Dynamic range
• Dynamic range – how many colors / how many
shades of gray
– High dynamic range: more bits per pixel
– Low dynamic range: may obscure features
B/W vs. color
• B/W: usually 1 byte per pixel
– Each pixel = grayscale number 0-255
– Ex. 180 is a brighter shade of gray
• Color: usually 3 bytes (24 bits) per pixel
– Each pixel has 3 values, each 0-255
– Ex. (200, 50, 128) = ?
– Most common scheme is RGB, where each pixel has
a red #, green #, and blue #.
RGB system
• Based on primary colors for light
• (red, green, blue)
• Examples
– Black = (0, 0, 0)
– Purple = (75, 0, 100)
– White = (255, 255, 255)
• How about (x, x, x) or (0, 0, x) ?
CS 111 – Sept. 8
• Finish image rep’n
• Adding binary numbers
• Integer rep’n in general
– Unsigned
– Signed
– Biased
 the most important of the 3
• Commitment:
– Meet here tomorrow
– Please read pp. 58-64
– Quiz Friday
RGB examples
Color
R
G
B
Black
0
0
0
White
255
255
255
Red
255
0
0
Green
0
255
0
Blue
0
0
255
Cyan
0
255
255
Magenta
255
0
255
Yellow
255
255
0
Q: How do we get “other” shades of blue?
Indexed color
• Do we really need 24 bits to represent color of
one pixel?
– This means we allocate 16,777,216 colors!
– About 200 would be more practical
• Indexed color is a “compressed” RGB
– 6 values of each primary color, not 256
– Use hex values 00, 33, 66, 99, cc, ff
– This is the color system used on the Web.
• 1 byte per pixel instead of 3
• Use “dithering” to simulate in-between colors.
Binary addition
• Analogous to decimal addition you know
• Only a few cases to consider – just watch out for carry.
– 0 + 0 = 0 (no carry)
– 0 + 1 = 1 (no carry)
– 1 + 1 = 10 (sum = 0, carry = 1)
– 1 + 1 + 1 = 11 (sum = 1, carry = 1)
• Example, 6-bit addition: 001110 + 001100
– Can check our answer in base 10
• Overflow: correct answer is beyond possible range
Integer rep’n
• How do we represent integers inside the computer?
– Scheme I: unsigned
– Scheme II: signed (a.k.a. Two’s complement)
– Scheme III: biased (a.k.a. Excess notation)
• Scheme I: Unsigned
– This is the scheme you already know.
– Cannot handle negative numbers.
– For n bits, possible range is 0 to 2n – 1.
• Scheme II: Signed
– Basic idea: half of the representations should be negative.
– Ex. For 5 bits, 16 of the 32 values are negative, so the range
goes from –16 to +15.
– For n bits, possible range is –2n–1 to 2n–1 – 1.
Signed rep’n continued
• How do we represent a number in signed?
• If positive, same as unsigned. 
– Ex. 6-bit signed rep’n of 13 is 001101.
– Ex. 6-bit signed rep’n of 31 is 011111.
(the largest #)
• If negative: 3 steps to represent –x:
1. Find rep’n of +x.
2. Invert the bits.
3. Add 1.
• Try some examples of negative numbers, and check
answers.
CS 111 – Sept. 9
• Integer representation: be able to convert both
ways (binary  decimal)
– Unsigned √
– Signed √
– Biased
• Real numbers
• Commitment:
– Please read sections 1.8 and 1.9
– Quiz tomorrow
Closer look…
• In 5-bit unsigned…
– Smallest number is 00000 (= 0)
– Largest number is 11111 (= 31)
• In 5-bit signed…
– Smallest number is 10000 (= –16)
– Largest number is 01111 (= 15)
• Given a bit pattern, its signed and unsigned values differ
by how much?
– Try some examples.
• In signed:
– Leftmost bit is the sign bit.
– Positive #’s have same rep’n as unsigned.
– Technique for –x doesn’t work for lowest number. Special case.
Signed + and –
• Signed + is like unsigned.
• Watch out for overflow.
–
–
–
–
The correct mathematical result can’t be represented.
(Pos) + (Pos) = (Neg)
(Neg) + (Neg) = (Pos)
Example: 01111 + 00001.
• To subtract, add the opposite. 
Example: 10111 – 00111
– First, –(00111) = 11001
– Turn into addition problem: 10111 + 11001 = __________
– Is there overflow?
Scheme III: biased
• Another way to represent integers that allows for
negatives.
• (It will soon help us see how real numbers are stored.) 
• The “bias” is the number we subtract from unsigned
range.
– If B is the bias, the lowest number is –B.
• When working with a biased rep’n, you have to be given
the bias.
– Ex. For 6-bits, bias is typically 31 or 32.
– Ex. For 8-bits, bias is typically 127 or 128.
• So, a “6 bit biased-31 rep’n” is based on 6-bit unsigned,
except that 000000 is now –31 instead of 0.
How to convert
• How do we represent a number n in biased (B)?
1. Add the bias: n + B.
2. Determine the unsigned rep’n of this number.
– Example: What is the 6-bit biased-31 rep’n of –9?
• It’s the same as the unsigned rep’n of –9 + 31 = 22.
• 22 in 6 bit unsigned is 010110.
• How do we convert a biased number back into base 10?
1. Interpret the number as unsigned
2. Subtract the bias.
– Example: 101010 is the 6-bit biased-31 rep’n of what number?
• If unsigned, 101010 = 32+8+2 = 42.
• 42 – 31 = 11.
Integer vs. Real
• Integer arithmetic on computer is quick & exact, but has
limited range.
• Real arithmetic needs wide range, and a reasonable
degree of precision.
– Scientific / numerical computation
– 14 significant digits is usually enough!
• Skills:
– Converting a base-10 real number into binary
– Actual representation relies on “scientific notation”
Examples
• Consider this sequence:
111 = 7
1110 = 14
11100 = 28
111000 = 56
1110000 = 112
• Going the other way…
111. = 7
11.1 = 3.5 or 7/2
1.11 = 1.75 or 7/4
.111 = 7/8
.0111 = 7/16
See the pattern?
Each digit corresponds to (+ /–) power of 2.
Convert to binary
• Separate real number (e.g. 5.7) into integer and
fractional parts
• Integer part  use binary store.
• Fractional part:
– Keep multiplying fractional part by 2 until it becomes zero, or
until you have a repeating pattern.
• Example: 9.625
– Integer part 9 becomes “1001”
– Fractional part is 0.625:
.625 * 2 = 1.25
.25 * 2 = 0.5
.5 * 2
= 1.0
Fractional part reaches 0. So our answer is 1001.101
Repeating pattern
• Let’ try converting 0.7 to binary:
.7 * 2 = 1.4
.4 * 2 = 0.8
.8 * 2 = 1.6
.6 * 2 = 1.2
.2 * 2 = 0.4
.4 * 2 = 0.8
• “Aha!” The pattern tells you which digits repeat.
____
• Answer is 0.1 0110 0110 0110 …
or .10110
Real number rep’n
•
•
•
•
Also called “floating point”
Size is 32 or 64 bits: “single” vs. “double” precision
Based on binary scientific notation
Let’s look at single precision:
– 1 bit for sign
(0 = positive, 1 = negative)
– 8 bits for exponent (expressed in biased-127)
– 23 bits for mantissa
• Big mantissa  precision is most important feature
Example
• We saw earlier that 9.625 = 1001.101 in binary. Let’s
continue with the true representation.
• Sign: 1 bit. Since it’s a positive number, we have 0
• Exponent: 8 bits
– If we write 1001.101 in binary scientific notation, we
get 1.001101 * 23.
– The exponent 3 is expressed in 8-bit biased-127. In
other words 3+127=130 in unsigned: 10000010
• Mantissa (23-bits): We only store the fractional part of
the mantissa: 001101. Remaining bits are zero.
• Final answer: 0 10000010 (1) 001101 017
Decoding
• Let’s see if we can decode a real number:
1 10000001 (1) 011 020
• Sign: “1” means a negative number
• Exponent: “10000001” looks like 129 in unsigned. But
in biased-127 it is 129 – 127 = 2. So our number is
something multiplied by 22.
• Mantissa: 1.011 in binary = 1 + 1/4 + 1/8 = 1.375
• Combine all 3 parts: –1.375 * 22 = –5.5
Some thoughts
• In single precision…
– 8 bit exponent  256 possible exponents
Highest number ~ 1038
Lowest number ~ 10–38
– 23 bit mantissa  ~ 8 million exact real number per power of 2
We have about 7 significant digits
• Comparing with double precision
– What can we conclude?
Precision
Sign
Exponent
Mantissa
Single
1
8
23
Double
1
11
52
CS 111 – Sept. 10
• Quiz
• Data compression
– text
– images
– sounds
• Commitment:
– Please read rest of chapter 1.
– Department picnic next Wednesday
Text compression
• Goal is for a document to take up less space
• Techniques
– Keyword encoding: replace common words by special symbols
like   ╞
– Run-length encoding: replace repetitions with a number:
“pppppppppppppp”  [14p]
– Huffman code: common letters should take up fewer bits
Huffman code example
• Suppose you want to send a message, and you know
the only letters you need are A, D, E, L, N, P, S.
• A Huffman code might look like this table:
A
D
E
L
N
P
S
001
100
01
101
0001
0000
11
• How would you decode this message?
01110000101001000100110001
How to create code 
• We’re given the set of letters used for the message, and
their frequencies.
– Ex. A = 5, B = 10, C = 20, D = 25, E = 30
– Ex. P = 5, N = 10, D = 10, L = 15, A = 20, S = 20, E = 30
• It’s convenient to arrange the frequencies in order.
• Group the letters in pairs, always looking for the smallest
sum of frequencies.
• The resulting structure is a “tree”. Each left arm = “0” in
the code; each right arm is a “1”.
Dictionary & LZW
• Dictionary encoding:
– Convert each word to a number
– Represent this number in binary
– If 50,000 words in dictionary, we can represent each with 16 bits
(2 bytes) since 216 > 50,000
– A lot shorter than the average word
• LZW
– Begin by encoding letters as 1-26, space as 27.
– Each time you form a new word, add it to the “dictionary” as 28,
29, 30, etc.
– So, we don’t need to encode every word in English language.
– Ex. AB ABC AB ABC would be 1,2,27,1,2,3,28,29
Image compression
• RGB 24-bit color represented as (huge) bitmap file *.bmp
• Most of the time, compressing an image is “lossy”,
meaning that uncompressing won’t restore original .bmp
information
• GIF compression uses indexed color
• JPG entails several steps
– Make tiny modifications to the image, so that neighboring pixels
will have more uniform values. For example, (10, 11, 12, 90) 
(11, 11, 11, 90)
– Use text/numerical compression techniques like run-length
encoding.
MPEG
• Motion Picture Experts Group
• Industry standard for compressing multimedia
• Note that much information in consecutive frames is the
same
• Delete sound information that humans can’t detect
• Goal: to make streaming video possible: 30 frames per
second at a minimal DSL connection
– Ex. 5-minute 300x200 video ~ 12 MB
CS 111 – Sept. 13
• Error detection
• Error correction
• Review/practice chapter 1 questions
• Commitment:
– Please read sections 2.1 and 2.2
Transmission errors
• When you send data over a network, there could be rare
random flipping of bits.
• Error Detection
• Error Correction
• One method of detection is using a parity bit
–
–
–
–
Add 9th bit to each byte during transmission
Goal is that each byte has even # of 1’s
Receiver checks each byte.
… Catches many but not all errors.
2-d parity
1
0
1
1
0
1
1
1
0
0
0
0
1
1
1
0
1
0
1
1
0
1
0
1
0
1
1
0
0
0
1
1
1
0
0
1
1
0
1
0
1
0
0
1
0
1
1
0
0
1
0
1
1
1
0
1
0
1
0
0
1
1
0
1
0
0
1
0
1
1
0
0
1
1
0
0
0
1
0
0
0
The 9th byte is called a check byte.
Error correction
• Useful if you think there may be a lot of potential errors,
such as a noisy transmission medium.
• Devise a “code” so that each symbol’s bit pattern is quite
distinct from all the others.
– In practice, this means longer codes. In other words, the 8-bit
ASCII code would not be enough.
• One technique: Hamming code
– Example code p. 71
– Idea for assigning code is Hamming distance:
comparing codes, count how many bits differ.
– When you receive an erroneous code, see which
letter it’s closest to. Then you can make a correction.

CS 111 – Sept. 15
• Chapter 2 – Manipulating data by performing
instructions
• “What is going on in the CPU?”
• Commitment:
– Please read through section 2.3
– Meet here tomorrow.
Basic anatomy
• Inside a computer are 2 parts
– CPU
– Memory
– These are connected by a data bus: an “HOV lane” where traffic
can go either way.
• CPU contains:
– ALU: arithmetic and logic unit
– Control unit: figures out what to do next
– Registers to hold values needed for calculation
• Memory (RAM) contains:
– Software: list of instructions the CPU needs to perform
– Data: Input and output values need to be stored while program
runs
Stored program idea
• Program = software = list of instructions for CPU to do
• Programs reside in memory
• CPU will do 1 instruction at a time
• For each instruction, we do the following:
–
–
–
–
Fetch it from memory
Decode – figure out what it means
Execute – do it
And then we continue with the next instruction… until the
program is finished.
Simple example
• A program to add two numbers.
• This program may reside at bytes 100-116 in RAM.
• The two numbers we wish to add are located at bytes
200 and 204 in RAM.
• We want the result to go into memory at byte 208.
• Program may go something like this:
–
–
–
–
Load the value at Memory[200] into register 1.
Load the value at Memory[204] into register 2.
Add registers 1 and 2, and put result in register 3.
Store the value from register 3 into Memory[208].
• Note that the bus is communicating instructions (RAM to
CPU) as well as data (both ways).
Machine language
• Unfortunately, instructions for CPU can’t be in English,
French, etc.
• Machine language = binary (or hex) representation of
our instructions.
– Each type of computer has its own machine
language.
• This is the oldest form of “computer programming”.
Later we’ll look at much more intuitive ways to convey
instructions. 
• Verbs: Instruction set. e.g. Add, subtract, load, store…
• Nouns: Operands such as: registers, memory locations,
constants, other instructions
Verbs
3 kinds of instructions (instruction set)
• Data transfer, using the bus
– Load a value from memory into a CPU register
Very similar to fetching an instruction!
– Store a value from a CPU register into memory
• ALU
– Bit manipulation: AND, OR, XOR, NOT, shift left, shift right, …
– Arithmetic: add, sub, mul, div, remainder, =, <, >, , , ≠, …
• Control
– “Go to” another instruction in program. In other words, interrupt
normal sequence of instructions.
– Can be conditional or unconditional
Example language
• Our book illustrates with an example HW.
• 256 bytes of RAM: addressable by 8 bits
• CPU contains
– Instruction register
– Program counter
– 16 general purpose registers: addressable by 4 bits
• Each register is 1 byte
• Each instruction is 2 bytes = 16 bits = 4 hex digits long
• Instruction format:
– First 4 bits are the opcode = specify which instruction type
– Other 12 bits are operand(s)
• What do instructions mean? See pp. 602-603.
Example instructions
• Note: 16 possible opcodes: 4 bit opcode
• Note: 16 possible registers: register number also 4 bits
• Opcode 5 is used for adding
– Expects 3 register operands
– 5RST means R = S + T, where R, S and T are register numbers
– Ex. 5123 means
Add registers 2 and 3 and put result in register 1.
• Opcode 2 is for putting a constant in a register
– Expects a register operand, and an 8-bit constant operand
– 2RXX means R = XX, where XX is some 8-bit pattern
– Ex. 27c9 means
Put the hexidecimal “c9” into register 7.
• Try an example using both types of instructions.
CS 111 – Sept. 16
• Machine language examples
– Don’t memorize…
• Instruction execution
• Closer look at operations in instruction set
• Commitment:
– Please read sections 2.5 and 2.6.
– Quiz next Wednesday.
More instructions
• Opcode 1 is for loading a memory value into a register
– Expects a register operand (4 bits), and a memory address from
which to load (8 bits).
– Ex. 1820 means to go out to memory at address [20], grab the
contents and load it into register 8. (It does not mean put the
number 20 in register 8.)
• Opcode 3 is a store = opposite of load
– Ex. 3921 means to take the value in register 9, and put it into
memory at location [21]. (It does not mean put the number 9 into
memory location 21.)
• Opcode C (hex code for 12) is for telling CPU it’s done.
– Expects operand to be 12 zero-bits.
Some practice
Refer to appendix C…
• How would we put the number 64 into memory at
address 12?
• How would we add the numbers 6 and 8 and put the
result in register 1?
• How would we add register 7 to register 5 and put the
answer in memory at address 32?
• More examples: p. 91
Execution
• In our example, each instruction is 2 bytes long.
• Program counter (PC) begins at address of first
instruction.
• For each instruction:
– Fetch (and increment PC by 2)
– Decode
– Execute
• Examples pp. 98-99
• Note that RAM contains both instructions and data,
separated from each other. For example, addresses 099 could be reserved for code.
Logic operations
• Work just like gates, but we do several bits in parallel.
• Examples
10101110
01101011
AND 11110000
AND 00011111
• Try the same examples with “OR” and “XOR”
• Observations:
– What happens when you AND with a 1? With a 0?
– What about OR’ing with a 1 versus a 0?
– What about XOR?
Shift operations
• Given a bit pattern like 00011100, we can shift the bits
left to obtain:
00111000.
• If we shift to the right instead, 00011100 becomes
this:
00001110.
• We can even shift by more than one position.
– Shifting 01010000 by 3 bits right  00001010.
• Sometimes when we shift, 1’s fall off the edge.
– Shifting 01010000 by 2 bits left  01000000.
• When we shift, the “vacated” bits are usually 0.
Why shift?
• One application of a shift operation is to:
– Multiply by 2: left shift
– Divide by 2: right shift
– Try some examples – should look familiar with our earlier work
on binary numbers.
• One funny exception: dividing a (signed) negative
number by 2.
– In this case, we want the vacated bit to be 1
– Example: –12 in signed is 11110100.
If we shift right by 1, we get 01111010, but it should be
this:
11111010.
Rotate
• Rotate operations work the same as shift… except that
the vacated bits come from the other end of the number.
• So, instead of 1’s falling off the edge, they rotate.
• For example, 01010000 rotated left by 2 becomes
01000001.
• Also: 00001111 rotated right by 3 becomes: 11100001.
• Examples pp. 103-104.
CS 111 – Sept. 17
• 2.5 Beyond the CPU and memory
– Peripheral devices
– Communication speed
• 2.6 Making the CPU faster
• Commitment:
– Please read sections 3.1 and 3.2.
– Quiz next Wednesday.
Devices & controllers
• device = some peripheral plugged into computer, usually
for I/O
• controller = a circuit that allows a device to send data
to/from CPU and memory.
• device driver = program that knows how to use the
controller. 2-way communication
• memory mapped I/O = Program can access controller by
referring to it with a memory address, as if it’s memory.
• Direct Memory Access (DMA) = allow controller to
load/store to memory while CPU is doing other work.
• USB: technology allowing one controller to handle a
variety of devices. Your machine has several USB ports.
Communication rate
• Used for both internal & network communication.
• Units
– “baud” = bit per second
– Kbps, Mbps, Gbps
– If there’s overhead/noise, figure on an average of 10 bits per
byte, so 1 Mbps = 100 KB per second.
– I can read a 20 MB file from USB drive in 2 seconds. What is the
bit rate?
• Voice telephone line – limited to 57.6 Kbps
• DSL, cable modem: “broadband” 50-100+ times faster
– Uses more of the sound spectrum; and data compression
Improving the CPU
• Pipelining
– Run the instruction like an assembly line.
– Partition the CPU: fetcher, decoder, executor
– Fetch instruction #2 at the same time it decodes #1; etc.
• Parallel or multi-processing
– MIMD = “multiple instructions, multiple data”
Take a large task and give parts to different processors
A central “node” collects final answer.
– SIMD = “single instruction, multiple data”
Good for: Small program, but a huge amount of data.
Each processor runs same program with small part of data.
Pipelining or not
• Without pipelining
F
D
X
1
• With pipelining
F
D
X
1
1
1
2
2
2
3
3
3
2
1
3
2
1
4
3
2
5
4
3
6
5
4
7
6
5
7
6
7
CS 111 – Sept. 20
• Operating Systems
–
–
–
–
definition
origin
responsibilities
relationship with other software
• Commitment:
– Please read pp. 131-137
– Quiz on Wednesday.
Original purpose
• Streamline process of doing jobs on the computer.
• Reduce overhead spent between jobs.
• Batch processing:
– Plan day’s jobs in advance
– Give jobs to a computer operator
– Job Control Language: enter commands to the OS
• Computer operator not practical
– Confidentiality
– Some applications like a game are inherently interactive; require
fast turnaround
Utilization
Historically…
• CPU time used to be very expensive
• 2 ways to run jobs
– Interactively
– In batch mode. This is useful if jobs must complete by some
deadline in a real-time system.
• Time sharing
– Many users, but just 1 expensive machine.
– Do not let any one job monopolize machine.
– Have several jobs running at same time; give each a turn at the
CPU: multi-programming
– Today: 1 user has many jobs per day – use same technique
Kinds of software
• Application – fun & useful stuff for people
– Hearts, Excel, Firefox, e-mail, PPT, …
• System utilities – programs that make the computer
more useful, added features
– Formatting a disk, compress data, play DVD
• OS shell – accept commands from user; display error
message
• OS kernel – major responsibilities; manage resources
• Note: distinctions can be blurred – the distinctions
among the categories are not exact
Responsibilities (1)
• Security
– Require many password combinations
– Penalties for mistake
– Super user & diagnostic tools to detect abnormal activity
• CPU
– Be aware of all currently running programs
– Synchronization: make sure 2 executing programs don’t
interfere with each other
– Scheduling: deciding which program to execute now
• Memory
– Decide which files (or portions of files) should be in RAM
– Virtual memory: shuffle pages in and out of RAM to give illusion
that RAM is bigger than it really is
Responsibilities (2)
• Files
– Maintain folders
– Keep information about each file: name, size, owner, type,
permissions
– User quotas
• I/O and network
– Device drivers
• User interface (shell or GUI)
CS 111 – Sept. 22
• Operating Systems
–
–
–
–
Booting
Processes
Scheduling
File permissions
• Commitment:
– Please read section 3.5
Boot cycle
• When you turn machine on, OS is on disk.
• CPU must begin running pre-arranged code in nonvolatile ROM.
• The ROM program tells the CPU to load OS from disk to
RAM.
– As well as BIOS: basic I/O system
• Finally, begin running the OS.
• ROM designed to be fast/efficient, therefore small. The
entire OS cannot fit in ROM.
Process
• A program that has started, but hasn’t yet completed….
Pending work.
• OS must keep track of all current work, in case of
interruption or hibernation.
• Possible states for a process
– Ready (could execute, but doesn’t have CPU)
– Running (in CPU)
– Waiting (doing I/O operation)
• During its lifetime, a process may experience many state
transitions.
CS 111 – Sept. 24
• Operating Systems
– Scheduling
– File permissions
• Commitment:
– Please read section 4.1
Scheduling
• OS may need to decide the order in which to do jobs
• Many ways to create a schedule. We’ll look at 2.
• First-come, first-served
– Do the jobs in the order in which they are requested
• Shortest Job Next
– Give priority to short/easy tasks.
• Evaluating schedules
– People are interested in how long for their requested jobs to
complete.
– Compute the average turnaround time.
– Turnaround time of a job = (time @ finish – time @ request)
Example 1
Process number
Time of request
Execution time needed
1
0
20
2
5
30
3
10
40
4
20
10
• First-come, first-served
–
–
–
–
Process 1 can execute from t=0 to t=20
Process 2 can execute from t=20 to t=50
Process 3 can execute from t=50 to t=90
Process 4 can execute from t=90 to t=100
• We can enter this info as extra columns in the table.
• What is the average turnaround time?
• What if we tried Shortest Job Next?
Example 2
Process number
Time of request
Execution time needed
1
0
10
2
30
30
3
40
20
4
50
5
Note that it’s possible to have idle time.
System load
• A measure of how “busy” the CPU is
• At an instant: how many tasks are currently running or
ready.
– If load > 1, the system is “overloaded”, and work is backing up.
• Typically reported as an average of the last 1, 5, or 15
minutes.
• Based on the schedule, can calculate average load as
well as maximum load.
File permissions
• 3 levels: owner, group, rest of world
• For each level:
– ‘r’ = Can I read the file?
– ‘w’ = Can I write to (or delete) the file?
– ‘x’ = Can I execute the file?
• Examples
– rw-rw-r-– rwxr-xr-– rw-r-----
(664)
(754)
(640)
Common permissions
• On many systems, there are no groups, so the group
permission is the same as “everybody else”.
• Examples
644
600
755
700
• Only a file/folder’s owner or the administrator may
change permissions.
CS 111 – Sept. 27
• Ch. 4 Networking
–
–
–
–
–
–
Topology of network
Protocols
How networks get used
Internet applications
WWW and HTML
security
• Commitment:
– Please read sections 4.2 and 4.3
Communication
• Claude Shannon’s model
– Source and destination of message
– Sender and receiver programs
– Transmission medium + noise
• Sender
– Must encode info in binary
– Encrypt if desired
– Package as required (parity bit, split into packets, etc.)
• Receiver
– Undo Sender’s tasks in reverse order
Topology
• Shape of network, usually in reference to a LAN
•
•
•
•
Point-to-point
Star
Token ring
Bus: Ethernet
Protocols
• Protocol = established rules on how to communicate;
etiquette on what to expect
• Ethernet protocol
–
–
–
–
Wait until bus empty before sending a message
Each message is broadcast so all can hear
Machines listen to see if message is for them
Detect collision
• TCP/IP
• Detect “hidden terminal” in wireless network
– Require all machines to periodically check in with “hub”
Long distance communication
• Repeater: amplify message in the bus
• Bridge: connect 2 networks
– Filter message – only allow message across if destination is on
the other network
• Switch: like a bridge, but a hub that connects several
networks (LANs)
• Router: Special purpose computer that forwards
messages according to destination address
– Internet & internet
– Connected networks can be quite heterogeneous
CS 111 – Sept. 29
• Ch. 4 Networking, continued
– Internet architecture
– Internet applications
– WWW
• Commitment:
– Review notes
Internet
• 1960s: the need for a “computer utility”
• Military, academic, commercial uses in its history
• Network of networks, connected by routers
• Maintained by ISPs worldwide
– Major ISPs are usually national telecoms
– Local ISPs may offer special service, as in a resort
– You access Internet by connecting to a “host” machine owned by
your ISP
Addresses
2 ways to express URL (Internet address):
• IP numbers
– Of the form a.b.c.d where each number ranges 0-255
– Ask your ISP for a batch of consecutive IP numbers for your
company.
– Ex. All Furman IP addresses begin 156.143
– Difficult to remember
• Domain names
– Dotted notation, but words/letters instead of numbers
– Top level domains regulated by national non-profit company,
whose monopoly is enforced by law.
– ICANN is the arbiter for IP #s and domains for the USA
• Name server can convert between address types
Applications
• Examples: E-mail, gopher, Web, FTP
• Usually connect with specific server that specializes in
that application
–
–
–
–
Server needs to have software that obeys relevant protocol.
Ex. Mail server needs to adhere to mail protocols, etc.
Ex. Web server needs to respond to requests for Web pages
Ex. FTP server should allow users to perform upload/download
and directory access
• Alternatively, you can log in to a remote machine
– Made possible with client programs Telnet or Putty
– Putty implements a “secure shell”: encrypts communication
WWW
• 24 years younger than the Internet as a whole
• World Wide Web = set of linked documents hosted on
specific machines called Web servers connected to the
Internet
• Each document has a URL (based on domain names)
• Web terminology:
–
–
–
–
Web server
Web page
Web site
Web browser
• Anatomy of a URL
CS 111 – Oct. 4
• Web design
– HTML
– Javascript
• Commitment:
– This week, read sections 4.3 – 4.5.
HTML
• Stands for: HyperText Markup Language
• Hypertext means a text document that contains links to
other documents
• Also may contain multimedia.
• HTML is interpreted by a browser
• .html file contains content as well as formatting and
layout commands
• Dreamweaver can hide these details from you
HTML (2)
• File format
<html>
<head> … </head>
<body> … </body>
</html>
• Head section is optional
• Body contains material to appear in browser window.
• What does simplest Web page look like?
Common tags
•
•
•
•
•
•
•
h1, h2, etc. = headings
br = line break
p = paragraph
b, i = font should be bold or italic
hr = horizontal rule
ol,ul, li = used for lists
sub, sup = subscript or superscript
• <img src=“name-of-image.gif”>
• <a href=“name of file or URL”> text to underline </a>
Javascript
• Can write simple programs with little or no prior
experience
• Purpose of JS is to give some interactive “life” to Web
pages.
• Works with a Web browser.
– First, create HTML file using editor or Dreamweaver.
– Refresh the browser when you make a change.
• Online guide for general reference
– http://www.w3schools.com/js/js_examples.asp
– We’re only going to scratch the surface
Simple JS features
•
•
•
•
•
Printing a message
Using variables
Looking up the time
Making choices
Doing something several times (a loop)
• A form inside HTML
– Can create form object in Dreamweaver.
– In Javascript, write instructions on how to handle the input.
CS 111 – Oct. 6
• Javascript practice
– See handouts.
– To get ready for lab.
• Commitment:
– This week, read sections 4.3 – 4.5.
– Quiz next Wednesday.
Examples
• js1.html:
–
–
–
–
I/O,
variables,
making choices
Let’s fix mistake with
printing time.
• js3.html:
– I/O,
– arithmetic,
– counting/repetition
• form1.html:
–
–
–
–
form object
text boxes
text area
function to inspect form’s
input & perform action
• form2.html:
– Function counts number of
correct answers
Form’s input
• You’ll see an expression like this:
document.survey.second.value
• We identify a form’s value with these 4 parts:
–
–
–
–
document = What Javascript calls the entire page itself
survey = name of the form (where is this in the HTML?)
second = name of text field in the form
value = contents of what user typed
CS 111 – Oct. 8
• Internet topics
– HTML & XML
– Client / server
– Internet layers
• Commitment:
– Read section 4.5.
– Quiz next Wednesday.
Markup languages
• HTML specifies format of Web page through <> and </>
commands.
• Commands convey a list of things, or are nested inside
other commands.
• Can be generalized to all other documents conveying
information.
• XML: a general markup language that can be used for
defining the format of any document
– One way of representing a “database”
• Example: KML is used to define geographic regions for
Google Earth.
XML example
<solar_system>
<planet>
<name>Mercury</name>
<orbit>88</orbit>
</planet>
<planet>
<name>Mars</name>
<orbit>687</orbit>
<moon>
<name>Phobos</name>
<order>1</order>
</moon>
<moon>
<name>Deimos</name>
<order>2</order>
</moon>
<planet>
<name>Neptune</name>
<orbit>60190</orbit>
// Specify 8 moons here
</planet>
// Specify more planets here
</solar_system>
Client & server
• You want to perform a business transaction with a
company via the Web.
• Internet software usually has 2 parts:
– Client program: Interactive Web site contains just enough code to
get data from the user, and transmit it to the company’s server.
– Server program: Process each client’s information.
• Why the separation?
– User (client) should not have to download entire program just to
buy something.
– User should not log into company’s computer. 
– Server has access to huge amount of proprietary and confidential
information.
– Many clients may want to do business at the same time.
Layers of communication
• Human layer
• Application layer: client/server relationship, e.g. between
your browser & host site.
• Transport layer: Your system breaks up messages into
packets. Choose desired Internet protocol (TCP or
UDP). Recipient assembles message.
• Network layer: Routers decide best direction to forward
packets.
• Link layer: Managing the traffic, the legwork of moving
packets.
• * Each layer communicates with neighboring ones.
CS 111 – Oct. 11
• Internet topics
– Network applications and technology for business
– Security
• Commitment:
– Quiz Wednesday.
– Homework #1 due Oct. 18: Discuss your favorite
infamous example of a computer crime. Why is it
significant, and could it happen again?
Network applications
• Both client and server software necessary
• Many are same as personal applications
– E-mail
– Voice mail
• But others are services that people expect from some
establishment
– Videoconferencing
– Bulletin board (i.e. forum)
– Electronic funds transfer, and credit card transactions !
Network architecture
• Within a company, may be centralized or distributed
• Need backups of software as well as data
– E.g. NASDAQ during 9/11
• Use a WAN to connect major operators (e.g. stores in a
chain)
• Network operating system
– Distinct from each machine’s OS
– Handle system logins and traffic in WAN
Download speed
• Overhead time – prepare and assemble message
• Flight time – first bit to arrive at destination
• Bandwidth – max rate to propagate data (Cruising
speed). Divide size by rate.
• Total time =
overhead + flight time + (msg size / bandwidth)
• Unless message is tiny, bandwidth is crucial issue.
• Rules of thumb for home users:
– Dial up: 10 MB per hour
– DSL: 10 MB per minute
Internet backbone
• Telecoms maintain traditional phone lines as well as
fiber optic cables.
• “T-carriers” range from T-1 (1.5 Mbps) to T-4 (274 Mbps)
– Your business can subscribe to dedicated continuous Internet
connection. Ex. Furman subscribes to 200+ Mbps level of
service.
• Fiber optic: OC-1 (51 Mbps) to OC-192 (10 Gbps)
• Fiber optic generally limited to urban areas
Security
• Areas include security of the…
–
–
–
–
Physical site (traditional notion of security)
IT resources – such as printer, files
Network – ability to communicate
Service – whatever the firm deals with
• Results of breaches:
–
–
–
–
–
Destruction of resources, information, service
Corruption of data
Denial of service
Theft
Fraud, e.g. cheating the company or defrauding the public
Security issues
• Viruses, Trojan horses, etc.
• Firewall for firm’s network
– Distinguish between intranet and Internet
– Firewall is any system that specifies what traffic to allow in either
direction
• Maintain backups of everything
– Note: Accidents happen. Power goes out, people delete files…
• Audit Internet traffic to/from site looking for anomaly
• Encryption: Make transmissions secure
– https and .shtml
CS 111 – Oct. 13
• With a network, you can make $: E-commerce
• Commitment:
– Homework #1 due Oct. 18: Discuss your favorite
infamous example of a computer crime. Why is it
significant, and could it happen again?
E-commerce
• Means the browsing, buying, and selling of goods and
services using public or private computer networks.
Two types of commerce:
• Business to consumer
– Web site used as the showroom.
– Some businesses exist only online. (amazon)
– Some sites are “portals” that tell you where to buy. Examples:
Kayak and salescircular. The travel-agent model.
• Business to business (the client is another business)
• Benefits and challenges of e-commerce?
• What are some goods/services that are easy vs. hard to
sell online?
Desired functions
• Advertise elsewhere, draw people in
• On Web site: provide product information
• Shopping cart
• Back-office processing
– Update inventory
– Process payment (credit card)
– Send goods to consumer, provide return mechanism
• This is on top of other ordinary business functions, such
as payroll, taxes, insurance, etc.
Behind the scenes
• Commerce usually involves the following players:
–
–
–
–
–
Supplier of raw materials
Manufacturer
Distributer
Retail outlet
Consumer
• Between each, there can be an e-commerce
relationship.
– Besides business-to-customer, we have “business-tobusiness” or B2B for short.
– Gives rise to a “supply chain”
Supply chain
• Need to manage flow of materials and $ between your
suppliers (upstream) and your customers (downstream).
– You don’t want to be sold out of an item.
– The business has its own bills to pay.
• Example goals where IT can help:
–
–
–
–
–
Keep inventory low, but not zero. (Detect when getting low.)
Cut cost of keeping inventory.
Reduce replenishment times.
Reduce transportation costs!
Perhaps outsource activities that do not add value to the
company ($ or reputation).
– Anticipate change, look at trends. (school supplies, Christmas)
CS 111 – Oct. 18
• Discuss computer crimes
– Ex. Cliff Stoll’s “Cuckoo’s Egg” or the video “The
KGB, The Computer and Me.”
• Commitment:
– Please read sections 5.1 and 5.2
CS 111 – Oct. 20
• Most essential skill in IT: problem solving using the
computer
– Telling the machine exactly what we want it to do.
– Also: making sure result of software is packaged in a
way that ordinary people will understand.
• Problem solving procedure
• What does a solution look like?
• Learn by example, and generalize.
• Commitment:
– Please read carefully sections 5.1 and 5.2
Why software?
• Want computational power
– To have direct control of machine
– Sometimes, existing software is not sufficient, doesn’t give what
you want
– Programs can be useful or fun for people to use (e.g. game,
converting data to image, …)
• Need to use a computer language
– E.g. Javascript, PHP, Python, C++, etc.
– Machine independent
– Many common calculations are pre-defined, such as sorting,
opening files, surfing the Web, creating a form button, etc.
Program
• One specimen of software is called a computer program
• Small or large, purpose is to solve 1 problem.
• Works like a recipe
– List of necessary ingredients
– List of instructions for CPU to obey.
• A simple program normally has 3 phases.
– Input
– Calculations
– Output
Recipes
• Cooking may be a good analogy, because it
solves the problem “I’m hungry” 
• What do we see in recipes? Here’s one:
–
–
–
–
–
–
–
Brown the beef 15 min. Drain grease.
Dice carrot, celery, onion (aka mirepoix)
Cut up and boil 6 potatoes until soft.
Mash potatoes
Add flour, spices, sauce, mirepoix to beef.
Put meat mixture into casserole; top with potatoes.
Bake in oven at 400 for 30 minutes.
Recipes (2)
• A computer program has some of the same
elements as a recipe.
• In recipes, we see:
– Ingredients (the “nouns” of the problem)
– Steps to perform (the “verbs”)
– In some steps, we continue/wait for something
– Sometimes we check things
• Are potatoes fully mashed?
• Should I add more _____ to the mixture?
Recipes inside recipes
• But we don’t eat the same stuff every day. Once we
know a few recipes, we can put together a menu for
choices.
if
if
if
if
(have all ingredients), make Shepherd’s pie.
(no potatoes), just make soup instead.
(no veggies), make hamburger.
(no beef), make pasta.
• When you view a whole menu as a program, then
“making soup” becomes a sub-program.
– A large program is composed of several parts.
– In industry, sometimes each part is implemented by different
people, like a kitchen having many chefs.
Problem-solving
1. Understand problem; inputs and outputs
2. Write solution in English “pseudo-code”
3. Write code in a programming language
4. Compile
5. Run and test
•
When program works, can refine or generalize.
CS 111 – Oct. 25
• What is a program? √
• Problem solving procedure √
• Step #2 is most important: write solution (algorithm) in
English
• Structure of solution:
– Sequence of steps (1, 2, 3, …)
– Sometimes make a choice
– Sometimes need to repeat
• Examples
• Commitment:
– Please read section 5.3
Problems
• The earliest problems given to a computer were
mathematical.
• Sometimes there is no clean formula
– Many equations can’t be solved analytically. For example: try
cos(x) = x. Need to solve numerically.
– Ex. Heat equation is a partial differential equation (PDE). Most
PDEs have to be solved numerically.
– Ex. Calculating a square root.
• Even if there is a clean formula, a computer can help
automate the calculations.
Problems (2)
• What kinds of problems do we solve?
– Finding directions
– Predicting trends (weather, finance)
– Games
– Record keeping in a business
– Networking and communication
– Multimedia (e.g. image processing, animation and
graphics)
– Compressing and encrypting data
– Searching for something (spell check)
–…
Algorithm
• A clear sequence of steps to arrive at a solution to a
problem. Must specify:
–
–
–
–
Ingredients
Input, output, variables and operations used
The order in which steps are taken
Means that anybody should be able to follow your directions.
There is no ambiguity.
• Ideally, each step should perform 1 calculation:
–
–
–
–
Input or output of 1 value
1 calculation, or 1 decision to make
Calculations usually limited to basic math
In your algorithm, tedious details can be put off until later.
Explain big picture first.
Examples
• Discuss in general how you would solve these problems:
–
–
–
–
Print the numbers from 1 to 100.
In this list (3, 2, 7, 5, 4) where is the number 5?
Which room contains my umbrella?
Have 2 people play Tic-Tac-Toe.
• Let’s practice fully with these problems:
– Ask the user to enter 2 numbers, and output their sum.
– Determine a person’s weekly wage, given the number of hours
worked and hourly rate. Don’t forget to figure in overtime.
– Add the numbers from 1 to 5.
Solutions
• Algorithm to add 2 numbers
–
–
–
–
Ask the user to enter 2 values.
Obtain the input, and call the values a and b.
Set a new variable sum and set it to: sum = a + b.
Output sum.
• Weekly wage
– Get hours and rate from the user.
– Set the wage as follows:
• If (hours > 40), use overtime formula
• Otherwise, use regular formula
– Output wage
Solutions (2)
• Add up the numbers from 1 to 5
– No input!
– Need 2 variables: sum and count
• The count variable will go from 1 to 5, one at a time.
• The sum will start at 0, and we continually add to the sum.
– Sum = 0
– Count = 1
– For each value of count from 1 to 5:
• Sum = sum + count
– Output sum
• If we can add 1-5, we can just as easily add 1-1000!
Mystery
• What does this algorithm do?
– No input.
– Create two variables: sum and count.
– Sum = 0
– Count = 1
– For each value of count from 1 to 20:
• Introduce new variable called temp
• Temp = count * count
• Sum = sum + temp
– Output sum
CS 111 – Oct. 27
• Practice problems
– See handout
– Work in pairs to devise solution to 1 problem
– We’ll discuss results
• Commitment:
– Prepare more solutions to practice problems
CS 111 – Oct. 29
• Continue working practice problems
• Commitment: Consider these problems
– How would you find the largest/smallest number in a
list?
– How would you count the number of values that are
positive?
– Counting vowels in a word.
CS 111 – Nov. 1
• Consider these problems
– Review searching
– Finding largest/smallest
– Counting things in a list
– More practice problems
• Commitment
– Read pp. 228-231 (insertion sort)
– Read #6 and #7 on pp. 232-233 (other ways to sort)
– Review sections 5.1 – 5.4
Search error
• What is wrong with this technique for searching for the
value 3 in a list?
list = { 8, 5, 2, 8, 3, 6, 1, 9, 4 }
for count = 0 to 8
if list[count] is 3
found = true
else
found = false
• How should we fix the mistake?
Largest / smallest
• How would you find the largest number in a list?
– Assume first number is the largest.
– For each of the other values, ask if it is larger than
what we think the largest value is. If so, update the
largest value.
– Also keep track of the location of the largest value, in
case that is also desired.
• Finding the smallest number is analogous
– What should we change?
Pseudocode
list = { 5, 7, 4, 2, 3, 8, 1 }
largest = list[0]
location = 0
for count = 1 to 6
if list[count] > largest
largest = list[count]
location = count
Output the largest and location in a sentence, e.g.
“I found the value 8 at position 5.”
Counting
• To determine how many values in a list are positive…
• First, need a separate variable, numPositive, initialized
to zero.
• Ask each number if it’s positive. If so, add 1 to
numPositive. No “else” clause is needed.
list = { -6, 0, 8, 4, 1, -2 }
numPositive = 0
for count = 0 to 5
if list[count] > 0
++numPositive
Output the value numPositive in a sentence.
Vowels
• A word can be thought of as a list/array of characters.
• Need a numVowels variables, initialized to zero.
• For each character in the word, see if it’s a vowel (a, e, i,
o or u). If so, add 1 to numVowels.
word = "serendipity“
length = strlen(word)
numVowels = 0
for count = 0 to length-1
c = word[count]
if c is a,e,i,o or u
++numVowels
Output numVowels in a sentence.
Programming note
• In PHP and other languages, if you need to ask several
questions inside in if-condition, you need to separate
each one with and/or as appropriate.
• Each individual condition must be a complete question.
• Illegal:
if (c == ‘a’ or ‘e’ or ‘i’ or ‘o’ or ‘u’)
if (x > 10 and < 20)
• Legal:
if (c == ‘a’ or c == ‘e’ or c == ‘i’ or c == ‘o’ or c == ‘u’)
if (x > 10 and x < 20)
Practice problems
• Given a list of numbers, how many are multiples of 5?
• Given a year, is it a leap year or not?
• Given a number, is it a prime number?
• Remaining practice problems from handout.
CS 111 – Nov. 3
• Finish practice problems: designing solutions in English
• Various ways of sorting
• Commitment
– Please read section 6.1
Examples
• Given a year, is it a leap year or not?
– Julian definition
– Gregorian definition
• Given a number, is it a prime number?
• Remaining practice problems from handout.
– Double letter (repeated value in a list)
– Triangles
Sorting
• Much studied problem in computing – many ways to do
it.
• Given a list, need to arrange it “in order”. Either
ascending or descending.
• Some methods do better based on type of data or how
the values are distributed.
• Enjoy this Web site demo of sorting methods:
http://cg.scs.carleton.ca/~morin/misc/sortalg
Some Methods
• Selection sort: Find the largest value and swap it into
first, find 2nd largest value and put it 2nd, etc.
• Bubble sort: Scan the list and see which consecutive
values are out of order and swap them.
• Insertion sort: Place the next element in the correct
place by shifting other ones over to make room.
• Merge sort: Split list in half until just 1-2 elements.
Merge adjacent lists by collating them.
CS 111 – Nov. 5
• Sorting
– Selection and Bubble √
– insertion: place next element in correct place by shifting over
other ones to make space
– Merge: Repeatedly split list in half until 1-2 elements each.
Then merge adjacent lists by collating them.
• Computer languages
• 3 kinds of software errors
• Commitment
– For next week, please read sections 6.2 (review); 9.1, 9.2
Language evolution
• Machine language
• Assembly language
– Like machine language, also unique to each manufacturer
• High-level language 
–
–
–
–
–
FORTRAN, COBOL
Pascal, Algol, Ada
C, C++, C#
Java, Javascript, Python
many more
Example
• How would we calculate:
12 + 22 + 32 + … + 202 ?
• Let’s create our own solution, and see what the “code”
looks like in different types of languages:
– Machine language 
– Assembly language 
– High-level language 
Machine language
00003000:
00004000:
00004004:
00004008:
0000400c:
00004010:
00004014:
00004018:
0000401c:
00004020:
00004024:
00000014
200c0001
20080000
3c0a0000
354a3000
8d4a0000
018a4822
1d200005
018c0018
00005812
010b4020
00004028:
0000402c:
00004030:
00004034:

218c0001
08001005
2008000a
0000000c
help me!
Assembly language
numValue: .word 20
__start:
addi $12, $0, 1
addi $8, $0, 0
lui $10, 0
ori $10, $10, 0x3000
lw $10, 0($10)
while:
sub $9, $12, $10
bgtz $3, end
mult $12, $12
mflo $11
add $8, $8, $11
addi $12, $12, 1
j while
end:
addi $8, $0, 10
syscall
HLL (Pascal)
var
sum : integer;
count : integer;
begin
sum := 0;
for count := 1 to 20 do
sum := sum + count * count;
writeln(sum);
end.
Bugs
• Any mistake made in a computer program
• Term ‘bug’ coined by Grace Hopper, ca. 1950
• 3 kinds of bugs
– Syntax errors
– Run-time errors
– Logical errors
• Beyond bugs, program can be just slow!
– Ex. Ineffective ways of finding the divisors of some number.
CS 111 – Nov. 8
• Databases
• Database Management Systems (DBMS)
• Structured Query Language (SQL)
• Commitment
– Please review sections 9.1 – 9.2.
Database
• A file containing 1+ tables
• Table = 2-d arrangement of data into rows and columns
– Rows correspond to “records” – info about 1 customer, 1
student, 1 animal, 1 house, whatever
– Columns correspond to “fields” – individual attributes about each
record. For example, name, address, phone number, ID
number, $ amount
DBMS
•
•
•
•
“Data Base Management System”
Software that allows us to manipulate a database file.
Most often, we want to query the database.
Examples:
–
–
–
–
–
Microsoft Access
Open Office Base
phpMyAdmin 
Oracle
Datatel
• SQL = Structured Query Language
– All DBMS support SQL
– We use SQL to communicate with the database.
SQL
• “Structured Query Language”
• DBMS accepts commands written in this language, so
we can manipulate the database file.
• DBMS may actually have point-&-click shortcut features
to save time on tedious tasks, such as entering all the
data, or creating tables from scratch.
• Most common SQL command is the “select” statement,
which asks the DBMS to return some of the data in the
database. Examples:
– Show me everybody’s address
– How many employees make over $100,000 ?
How to begin
• Create the database file
• Create first table: specify its format
– For each field (column), it needs a name, data type and
maximum length.
– Common data types are:
– Int/number
– Date
– Varchar (“variable-length character string”). Here you must
specify a maximum length, such as 20 characters.
– Sometimes, you may want to indicate whether a field is required,
must have unique values, etc.
• Enter data into the table.
• Make queries about the table.
Example
An Employee table:
First
Last
Location
Title
Salary
Peter
Jacobs
Brussels
Broker
55000
Denise
Lambert
Brussels
Accountant
42500
Robert
Nijs
Brussels
Broker
66700
Ruth
Molloy
Chicago
Manager
68650
Declan
Murphy
Chicago
Accountant
84125
Susan
Patterson
Chicago
Economist
51000
Rachel
Brady
Cincinnati
Broker
43300
David
Cunningham
Cincinnati
Accountant
48000
John
Whelan
Cincinnati
Broker
60500
Yvonne
Butler
San Diego
Broker
48500
Veronica
Keating
San Diego
Broker
72000
Mary
Walsh
Dublin
Accountant
46850
The select statement
• Very commonly used in SQL.
• Some possible formats:
select columns from table;
select * from table;
select columns from table where condition;
• Examples:
select First, Last from Employee;
select Last, Location, Salary from Employee;
select Last, Salary from Employee
where Salary >= 70000;
select * from Employee where Location = “Dublin”;
select * from Employee where Last like “M%”;
Aggregate functions
• In SQL, we can ask questions that involve arithmetic,
such as finding the max, min, avg of numerical values.
select max(Salary) from Employee;
select min(Salary), max(Salary) from Employee;
select avg(Salary) from Employee
where Location = “Chicago”;
select avg(Salary) from Employee
where Title = “Broker”;
CS 111 – Nov. 10
• Structured Query Language (SQL)
– We’ve already seen simple select statements, with optional
“where” clause and aggregate functions.
– More example commands today
• Relational database
• Commitment
– Review for test after lab
Log in
• As you will see in lab, you first need to “log in” to the
database management system in order to see your
database.
• From a Web browser, go to cs.furman.edu/phpMyAdmin/
• Enter your database username & password
• (Demo)
• If your SQL commands are incorrect, you’ll get error
message.
Example
An abridged Employee table:
First
Last
Location
Title
Salary
Peter
Jacobs
Brussels
Broker
55000
Denise
Lambert
Brussels
Accountant
42500
Robert
Nijs
Brussels
Broker
66700
Ruth
Molloy
Chicago
Manager
68650
Declan
Murphy
Chicago
Accountant
84125
Susan
Patterson
Chicago
Economist
51000
Rachel
Brady
Cincinnati
Broker
43300
David
Cunningham
Cincinnati
Accountant
48000
John
Whelan
Cincinnati
Broker
60500
Yvonne
Butler
San Diego
Broker
48500
Veronica
Keating
San Diego
Broker
72000
Mary
Walsh
Dublin
Accountant
46850
Distinct
• Sometimes in SQL you have a lot of repeated data. And
you only want the values themselves, not the repetitions.
– Ex. 70, 70, 70, 80, 80, 80, 80, 80, 100  70, 80, 100
• Examples
select Test2 from Student;
gives all test grades
select distinct Test2 from Student;
only shows each value once
select distinct Test1, Test2 from Student;
finds distinct pairs. 70/60, 70/80, and 90/80 are
considered distinct.
Group by
• The “group by” clause is good at finding subtotals.
• Example: how many employees by job title:
– Select count(first) from Employee group by Title;
– Actually, doesn’t matter which field we count.
• To make output easier to understand, we should also
print out the job titles:
– Select Title, count(Salary), avg(Salary) from Employee
group by title;
• We can even subtotal by 2 fields: What would this
command mean?
– Select Location, Title, count(Salary) from Employee
group by Location, Title;
Order by
• This clause is used for sorting.
• Default order is ascending.
• select * from Employee order by Last;
• select * from Employee order by Location, Last;
• select * from Employee where Salary > 50000
order by Location, Title;
More on “where”
• Boolean conditions: when you use the “where” clause
can include the word “and” or “or” to make complex
conditions.
– Ex. What if we wanted salaries of employees with names
starting with M or P.
• Use “in” when you want to select among several possible
values. Has the same effect as “or”
– Select * from Employee where Location in (“Dublin”, “Chicago”);
• Use “between” for an (inclusive) range of values to check
– Select * from Employee where Salary between 60000 and
70000;
Relational Database
• Databases with just 1 table are not very powerful.
• More interesting if 2 tables are related.
– Books and publishers
– Customers and orders
– Pets and owners
• Typically we have a “one-to-many” relationship
• The two tables need to have a field in common.
– You can see this if you try to list the necessary fields in the
above examples.
• In SQL, to refer to a field within some table, we use the
dot notation: Customer.First, Pet.Name, Order.ID
CS 111 – Nov. 15
• Relational database
• Detecting the 1-many relationship
• Primary key
• Commitment
– Please read section 9.2
Overview
• An “entity” is something that you want to maintain
information about.
– A university needs to keep track of students, employees,
courses, classrooms, housing accounts, athletic teams, special
events, etc.
– We create a table to store entities of the same type.
– Each entity becomes a record (row) in a specific table.
• Each entity has attributes – details about itself.
– Vary widely depending on the type
– Columns of table.
• A database usually comprises “related” tables.
Goals
• Integrating information from > 1 table 
• Reduce redundancy
– In other words, having unnecessary fields in a table.
– Redundancy leads to errors and waste
– Ex. Consider what info is necessary in a table listing all course
enrollments by all students.
• Maintain integrity
– Secure and reliable information
• Allow for change
– Inserting, deleting information… even creating new tables when
needed
Relational Database
• Real databases have 2+ related tables.
– Books and publishers
– Customers and orders
– Pets and owners
• One-to-many relationship
– The two tables need to have a field in common.
– You can see this if you try to list the necessary fields in the
above examples.
• Primary key
– A field that is unique for each record.
– This is usually the field used in defining a relationship.
Query
• In SQL, to refer to a field within some table, we use the
dot notation: Customer.First, Pet.Name, Order.ID
• Dot notation also avoids ambiguity
– Two different tables may coincidentally have same field name.
• In general, select queries are long enough that we
should write them out on 3-4 lines, not 1 long line:
• Example
select Customer.First, Customer.Last, Pet.name
from Customer, Pet
where Customer.CID = Pet.CID;
• We enforce relationship by matching ID #’s.
CS 111 – Nov. 17
• Enterprise databases
– Goals
– Examples
– Many-to-many relationship
– Restricting one’s view of entire database
– Design considerations
– Concurrency
• Commitment
– Homework #2 due Nov. 29
Goals
•
•
•
•
Retain and please customers
Attention to detail
Share data across company
Allow employees to “view” the portion of the database
relevant to them
• Quick response to employee or customer query
– Customers can interact with database via Web site
– Also: allow concurrent access
• Distributed database
– Client capability at point of sale
– Server capability at HQ
– Don’t keep all data in one place: allow for physical partition or
replication
Examples
• Luxury hotel
– Goal: Personalized attention to detail
– Store customer preferences for repeat visits
– When cleaning room, take note of pillows used, newspapers,
drink bottles and snack wrappers discarded
– Log requests, compliments, complaints
– On next visit, provide complimentary item as token of recognition
• Garage
– Take note of odometer reading
– Do they only come in for oil change? Give birthday discount on
other service
Not 1 database
• A large company probably needs more than 1 database,
each with its own purpose
–
–
–
–
Inventory control (materials, parts, finished goods)
Sales (customers and orders)
Manufacturing (production schedule, which factory)
Accounting (corporate taxes, dividends, payroll)
• Within a database, could have several tables:
• Example: Customer, Orders, Order Details, Product
– Many-to-many relationship
CS 111 – Nov. 19
• Enterprise databases, continued
– Review tables, joins, queries
– Restricting one’s view of entire database
– Design considerations
– Concurrency
• Beyond the database
– Other systems you might see in business.
• Commitment
– Please read sections 7.1 – 7.3
– Homework #2 due Nov. 29
Views
• view = subset of a database
– Details not relevant to you are hidden
• When you access a database, it is for a particular
function (data entry, lookup). Each function has its own
view.
• Some information is confidential
• Ex. Customer order history
– Contact info not needed
• Ex. Item order history
– Customer info, quantity of item on hand not needed
• This is why many queries are not “select * …”
Database design factors
• Storage cost, Also the need for backups (reliability)
• Processing cost:
– Do we have a powerful enough server?
– Are database operations implemented efficiently?
• Communication cost: Bandwidth and ISP server cost
• Retrieval and processing: confirmation response time
– Making all information available to everyone in company may be
impractical.
– Find out what info people need most often
• Frequency of updates and queries
– How often the store should send records to HQ
Concurrency
• Allowing several people to access database at same time
• Example:
–
–
–
–
Suppose there’s 1 seat left on tomorrow’s flight 17.
Customers A and B simultaneously query availability for that flight.
A buys a ticket.
B’s screen still shows 1 seat available. B also buys a ticket.
• Problem is that the purchase is not instantaneous
(especially major purchase)
– 2 transactions can overlap.
• Possible solution: record locking
– Each seat on flight is a record in some table.
– B cannot purchase seat, because A has already begun process of
selecting and buying ticket.
Beyond database
• We need data in IT (e.g. kept in a database), but that is
not enough!
• Transaction processing systems
– Add record to “order” table 
– Support queries and summary reports
– Automatic reporting of suspicious transactions (mistake, fraud?)
• Management info systems
– Provide information to make decisions:
– How much merchandise to order? How many people to hire?
Cheapest way to do ___
– These problems require general problem solving skill
• Other similar “support systems” also exist for specialized
purposes.
Big IT tasks
• To make IT work, people are more important than HW or
SW. Here are some examples.
• Database administrators
– Deal with database design, performance, security
• Systems analysts
–
–
–
–
Analyze large problems (e.g. some IT service for company)
Estimate time & personnel needed to get jobs done
design large applications; may write mock-up prototype
draw up precise I/O and performance specifications
• Project managers
– Deal with day-to-day responsibilities
– Maintain implementation schedule, with deliverables
• Software engineers
Sample IT questions
Feel free to paraphrase… Plus: Answers to one question
may prompt you to ask a follow-up question.
• What does IT encompass at your company?
– What % of your employees are mostly involved in IT?
– What sort of tasks need to get done?
• Do you have systems analysts at your company? What do they do?
– What other IT occupations do you have?
• What skills (technical & nontechnical) or traits are needed for people
who work in IT?
– Specific knowledge and conceptual understanding
• What is a typical career path for someone in IT?
• What is most rewarding aspect of working in IT? Most challenging?
CS 111 – Nov. 22
Chapter 7
• Software engineering
• Systems analysis
• Commitment
– Please read Section 7.4 (only pp. 336-341), Sections 7.6-7.9
– Homework #2 due Nov. 29
Software engineering
• Large software systems cannot be written by 1 person
• Several people work together
– Each is responsible for portion of program
– These portions interact… so must make sure your piece will fit
correctly in jigsaw puzzle
– Example: developing user interface for registration system:
Your output (list of desired course sections) must be in format
expected by next phase of program
– Deadlines
Tips for success
• General guidelines
–
–
–
–
–
Don’t reinvent the wheel
Make your solution efficient, elegant, easy to understand
Build solution incrementally, test & document often
It’s easier to fix a bug the sooner it’s found!
Work in pairs, check each other’s work
• Integrated development environment (IDE)
–
–
–
–
Software that simplifies job of writing code
As you type, “code” becomes color coded
Automates compiling and testing
Built-in debugger: can trace through instructions one by one,
inspecting values of variables: rather than modifying code by
inserting print statements!
Software life cycle
• Very similar to problem solving procedure
1. Problem specification written
2. Design of solution
3. Implementation
4. Testing
5. Maintenance
Systems analysis
• Distinction…
– Software engineering is mainly concerned with implementation
of the project
– Systems analysis is mainly concerned with specification and
design
• Definition of systems analysis (Whitten & Bentley):
– “A systems analyst facilitates the study of the problems and
needs of a business to determine how the business system and
IT can best solve the problems and accomplish improvements
for the business.”
– The finished product is eventually a new or improved computer
application, implemented by software engineers.
Principles
• Get the owners and users involved
– The program you’re designing doesn’t belong to you. It’s to help
other people. Find out what they desire.
• Follow problem solving procedure
– Define what a suitable solution must accomplish / do.
– Evaluate possible algorithms, and choose the best
– After testing, evaluate new system’s impact, get feedback from
stakeholders.
• Establish a schedule for the software life cycle
– How much time do you have
– How many people can you have on your team & for how long?
– What are their strengths and weaknesses?
Principles (2)
• Establish coding and documentation standards
– Your software engineers are writing code for you. Almost like
they are students in your class.
– Essential to have code written in a consistent style
– Encourage good documentation  communication, including list
of known problems. Let your people know they won’t be
penalized for admitting their work is incomplete. You don’t want
these to be a secret, or else risk future debugging.
– Give people a list of deadlines of deliverables.
– Have your team members meet with you to discuss their
accomplishments.
• Is the project work cost-effective?
– May need to scale down, trim some functionality or put off to
later version.
Principles (3)
• Beware the “mythical man-month”
– Doubling your staff will not make project take half the time. IBM
found this out the hard way in its System/360 project.
– Diminishing returns
• Don’t be afraid to scale down or cancel project
– Project should have milestones / checkpoints to evaluate path
toward success
– Decide how to get back on track, or reduce scope of project.
– Can final deadline be extended?
– If doomed, abort project and cut losses.
– But, will your superiors understand?
Principles (4)
• Divide and conquer
– A large project can be overwhelming at first. Break into small,
manageable parts.
– Reminds me of studying for a final exam, or writing large essay.
– Top-down design and bottom-up implementation.
• Design for future growth and change
– Your project may be in service for 10+ years
– People who adopt and like your work may want to continue using
it forever.
– You will have to live with decisions you make today. (For
example, choice of programming language)
CS 111 – Nov. 29
• Today: findings from your interviews
• Starting Wednesday: how to think like a systems analyst
– Finish basic principles
– Examples of possible problems and opportunities
– Problem solving approach from systems analysis point of view
• Commitment
– Please read Sections 7.6-7.9
CS 111 – Dec. 1
• How to think like a systems analyst
– Finish basic principles
– Examples of possible problems and opportunities
Refer to handout.
– Problem solving approach from systems analysis point of view
• Commitment
– Please read Sections 7.6-7.9 if you have not done so already.
Principles
• The guiding principles of systems analysis…
• Ones we’ve seen already:
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Get the owners and users involved
Follow problem solving procedure (we’ll elaborate later)
Establish a schedule for the software life cycle
Establish coding and documentation standards
Is the project cost effective?
Beware the “mythical man-month”
• Remaining ones:
– Don’t be afraid to scale down or cancel project
– Divide and conquer
– Design for future growth and change
Principles (3)
• Beware the “mythical man-month”
– Doubling your staff will not make project take half the time. IBM
found this out the hard way in its System/360 project.
– Diminishing returns
• Don’t be afraid to scale down or cancel project
– Project should have milestones / checkpoints to evaluate path
toward success
– Decide how to get back on track, or reduce scope of project.
– Can final deadline be extended?
– If doomed, abort project and cut losses.
– But, will your superiors understand?
Principles (4)
• Divide and conquer
– A large project can be overwhelming at first. Break into small,
manageable parts.
– Reminds me of studying for a final exam, or writing large essay.
– Top-down design and bottom-up implementation.
• Design for future growth and change
– Your project may be in service for 10+ years
– People who adopt and like your work may want to continue using
it forever.
– You will have to live with decisions you make today. (For
example, choice of programming language)
How to begin
• How does a big project (e.g. “information system”)
begin?
• Planned by the system analyst:
– The system analyst could be asked to poke around and look for
problems or opportunities for improvement.
• Or it’s unplanned:
– Request from management
– People using the current system complain
– If there are lots of requests/complaints, someone needs to
decide how to approved
• Purpose of the project is to respond to a problem,
opportunity or directive
Example
• Here’s a hypothetical example of a directive that could
affect a business system.
• Congress could enact a law requiring anyone buying an
international airline ticket to have a valid passport.
• The FAA specifies how this law will be enforced by
writing a regulation for the airlines:
– Airline must ask customer to provide country and number of
passport when they buy an international ticket.
– Airline must look up the passport number on a system provided
by State Department.
– If number invalid, reject transaction and refund customer’s
money.
– This functionality must be implemented for any mode of buying a
ticket (online, in person, over phone, etc.)
Brainstorming
• Where does one look for problems to solve, or
opportunities to exploit? One approach is the “PIECES”
framework:
• P = improve Performance
• I = improve Information
• E = improve Economics (i.e. profit and costs)
• C = improve Control (including security)
• E = improve Efficiency
• S = improve Service
• See handout for details
– Which categories seem most important to you?
CS 111 – Dec. 3
• Lab recap
• Problem solving approach for systems analysts
– 8 phases
– Just understand the flow/process/sequence of the steps, not
specifically how many there are or what they are called.
Important to understand the order of the steps is not arbitrary.
– Similar to problem solving approach for small programs we
would do in this class
– Much more emphasis on pre-design aspects
• The overall technique can be applied in other areas 
like planning a vacation.
• Commitment
– Review PIECES framework to prepare for in-class activity.
Approach
• Survey phase
– Define the scope, budget, staff, schedule
Scope: Is this a quick fix … or major overhaul?
– Is the project worth our time & money?
– Look over PIECES framework for ideas.
– Should be done in 2-3 days.
• Study phase
– Okay, let’s do the project. What are the relevant business
issues? (Technical issues come later)
– How beneficial will it be to do it? How much time/money should
we invest?
– List all the objectives you hope to accomplish.
– Understand the problem – are the objectives specific enough?
– External deadline?
Approach (2)
• Definition phase
– Critically important. At end of this phase, the definition
document is like a contract that should not change.
– What are the business requirements for a solution?
– Need to know specific requirements for: data, geography,
interface, process
– Build a prototype, and get it approved before continuing.
• Configuration phase
– Evaluate possible solution strategies. Look at various options.
– Should we outsource; how much should we do ourselves?
– For each candidate solution, find out, for example:
• Can we afford it?
• Will it actually work?
• Can we get it done on time?
Approach (3)
• Procurement phase
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What should we buy?
Do we need new or different kind of equipment, software?
Get proposals from vendors; negotiate.
Note there are fixed + variable costs.
• Design phase
– Tell how to solve the problem in technical terms. This is like step
2 from our original procedure.
– Decide in what order the components need to be implemented.
– Come up with an evaluation (testing) plan so that you’ll know the
implementation matches the design.
Approach (4)
• Construction phase
– Implement and test the solution, or an interim benchmark if it’s a
long-term project
– Test the individual components in isolation; test entire system
when ready.
– Most work is done by programmers, overseen by project
managers, etc.
– Caution: many “testers” are entry-level workers and may need
extra help/supervision.
• Delivery phase
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Install the HW and SW
Train people on the new system
Put it into daily use.
Put together a plan for regular support and maintenance.
Activity
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•
•
•
Next time: Let’s divide into 3 groups.
Each group will address an aspect of a problem
Let’s examine Furman’s class registration system
3 tasks (1 per group)
– Critically examine and evaluate the current system of preregistration and drop/add. Do you like it? Does it work? How
could it be improved? Cover all aspects such as technology, I/O,
ease of performing tasks, performance, red tape.
– What are the requirements of a good class registration system?
– How should the Web interface be designed? What feedback
and information should be available to users online?