Computer Science 1000
Terminology IV
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Software
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a collective term for computer programs
recall our definition for a computer program
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a sequence of instructions designed to perform a task
a true definition should also include data, as most
programs include non-instructional data as well
examples of data: button labels, menu items, numbers,
etc
note that both instructions and data stored as binary
sequences
software is typically classified into two types
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Software - Types
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1) Application Software
designed to perform a user task
 basically, the programs you are used to using
 examples:
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text editing (notepad, Word)
spreadsheets (Excel, Calc)
browser (Chrome, Firefox, Internet Explorer)
music (iTunes, Windows Media Player)
many others
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Software
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2) System Software
designed to perform system tasks
 they support the applications that you use
 examples:
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operating systems (O/S)
drivers*
loaders*
utility programs*
and others
* These are sometimes considered part of the operating system.
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MultiTasking
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consider your typical desktop experience
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you are probably running several programs at once
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e.g. you are typing notes while surfing Facebook and
updating Twitter
this "simultaneous" execution is known as multitasking
in order for a program to "run", its instructions have to
execute
how is it that one CPU core is able to run more than one
program simultaneously?
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MultiTasking
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as it turns out, each core will only execute a single program at
a time
in other words, programs have to share processor time
a core will execute a program for a small amount of time (a
time slice), and then start executing another program
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this change is known as a context switch
typical time slice lengths: 10-100ms*
these switches occur so quickly, that to us, it appears
that the programs occur simultaneously
*http://www.stanford.edu/class/cs140/cgi-bin/lecture.php?topic=scheduling
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Loading a Program
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recall that programs are stored on your hard drive
when not in use
to run a program, it (or part or it) is copied into RAM
this is known as loading a program
how does loading take place?
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another program, called a loader
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A Few Unresolved Issues
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multitasking
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program loading
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how does a processor know which program to switch to on
a context switch?
what defines the length of a time slice?
how does a processor know where a program exists in
memory?
what decides where a program is loaded in memory?
Answer: the operating system
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Operating System
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the most important software on your system
a collection of programs that perform many of these
tasks:
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allocate CPU time to programs
loads and manages programs in RAM
keeps track of files on your hard drive (file system)
facilitates communication with devices like keyboard,
mouse, display, etc
and much more!
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Popular Operating Systems
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Windows
developed by Microsoft
 first released: 1985
 the most popular operating system
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82% market share (December 2012)
http://www.netmarketshare.com/operating-system-market-share.aspx?qprid=8
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Popular Operating Systems
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MacOS
developed by Apple for their computers
 first released: 1984
 excluding Windows, comparatively popular
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6% market share
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Popular Operating Systems
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Linux
developed by Linus Torvalds
 first released: 1991
 1.27% market share, but fills niche roles
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supercomputers (90% of worlds fastest)*
servers (64.7% market share)
academics
most variants are free!
*http://www.top500.org/
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Input/Output
almost always referred to as I/O
 refers to the process of:
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input
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output
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reading data into the computer
sending data out of the computer
occurs via ports on your computer
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Input – Sources
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the obvious ones:
keyboard
 mouse
 game controller
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the not-so-obvious ones
internet connection
 external hard drive
 webcam
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Output – Sources
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the obvious ones:
display
 speakers
 printer
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the not-so-obvious ones
internet connection
 external hard drive
 game controller (force-feedback)
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Note that
devices can be
both input and
output.
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Two Neat Facts about I/O
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1) It's typically slow ...
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... by comparison to other operations in your
computer
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e.g. consider how many CPU cycles occur between
user keystrokes/mouse clicks/webpage loads
often, a program that is waiting for I/O will be
context-switched (so that processor stays busy)
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Two Neat Facts about I/O
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2) It requires a driver
different devices have different communication
protocols
 for a program to communicate with a device, it
has to speak its language
 a driver is a program that acts as a translator
between other programs and its device
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"Concept" Terminology
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certain terms refer to concepts that:
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we consider a few here
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are not specific to computer science
often used in computer science
algorithm
abstraction
your textbook discusses others
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generalization, factors of improvement, operational
attunement, mnemonic, etc ...
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Algorithm
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a precise and systematic method for solving a
problem – Text
notice anything about this description?
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no mention of hardware
no mention of software
in other words, algorithm is not computer science
specific
however, algorithms and computer code are often
used interchangeably
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why?
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Algorithm – Example
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write an algorithm for making a chocolate cake
(assume you have correct ingredient amounts and
supplies.)
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Step 1:
Step 2:
Step 3:
Step 4:
Step 5:
Step 6:
Melt chocolate and butter
Stir sugar into melted chocolate
Mix in flour
Spread mix in greased pan.
Bake at 350F for 40 minutes
Cool in pan
http://www.gmtel.net/web/windowshelp/algorithm.htm
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Algorithm
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not all algorithms execute in such a linear fashion
1) some steps may not execute under certain
conditions
example: algorithm for making a salad
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Step 1:
Step 2:
Step 3:
Step 4:
Step 5:
Add lettuce to bowl
Add tomatoes to bowl
Add carrots to bowl
Add dressing to bowl if I am not on a diet
Add croutons to bowl
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Algorithm
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not all algorithms execute in such a linear fashion
2) some steps may execute more than once
example: algorithm for washing hair
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Step 1:
Step 2:
Step 3:
Step 4:
Add shampoo
Lather
Rinse
Repeat Steps 1-3 until hair is clean
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Algorithm and Programming
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many people equate programming with coding
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programming largely involves:
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e.g. if you know code, you are a programmer
this is a bit like saying if you know English, you are a writer
developing an algorithm
converting that algorithm to code
the following is an example from my 1620 class
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not necessary to understand the code – the point is to
illustrate this process
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Example (Text): Write a program to compute the perimeter and
area of a rectangle. The length and width of the rectangle will be
specified by the user.
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Algorithm
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Step 1:
Step 2:
Step 3:
Step 4:
Step 5:
Read the length of the rectangle from the user.
Read the width of the rectangle from the user.
Compute the perimeter of the rectangle.
Compute the area of the rectangle
Output the results of this computation to the screen.
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Design (area and perimeter calculation)
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Step 1: Read the length of the rectangle from the user.
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Step 2: Read the width of the rectangle from the user.
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Step 3: Compute the perimeter of the rectangle.
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Step 4: Compute the area of the rectangle
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Step 5: Output the results of this computation to the screen.
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Design (area and perimeter calculation)
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Step 1: Read the length of the rectangle from the user.
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Step 2: Read the width of the rectangle from the user.
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Step 3: Compute the perimeter of the rectangle.
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Step 4: Compute the area of the rectangle
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Step 5: Output the results of this computation to the screen.
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Design (area and perimeter calculation)
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int length;
cout << "Please enter the rectangle's length: ";
cin >> length;
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Step 2: Read the width of the rectangle from the user.
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Step 3: Compute the perimeter of the rectangle.
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Step 4: Compute the area of the rectangle
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Step 5: Output the results of this computation to the screen.
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Design (area and perimeter calculation)
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int length;
cout << "Please enter the rectangle's length: ";
cin >> length;
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Step 2: Read the width of the rectangle from the user.
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Step 3: Compute the perimeter of the rectangle.
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Step 4: Compute the area of the rectangle
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Step 5: Output the results of this computation to the screen.
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Design (area and perimeter calculation)
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int length;
cout << "Please enter the rectangle's length: ";
cin >> length;
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int width;
cout << "Please enter the rectangle's width: ";
cin >> width;
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Step 3: Compute the perimeter of the rectangle.
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Step 4: Compute the area of the rectangle
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Step 5: Output the results of this computation to the screen.
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Design (area and perimeter calculation)
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int length;
cout << "Please enter the rectangle's length: ";
cin >> length;
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int width;
cout << "Please enter the rectangle's width: ";
cin >> width;
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Step 3: Compute the perimeter of the rectangle.
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Step 4: Compute the area of the rectangle
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Step 5: Output the results of this computation to the screen.
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Design (area and perimeter calculation)
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int length;
cout << "Please enter the rectangle's length: ";
cin >> length;
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int width;
cout << "Please enter the rectangle's width: ";
cin >> width;
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int perimeter = 2 * (length + width);
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Step 4: Compute the area of the rectangle
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Step 5: Output the results of this computation to the screen.
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Design (area and perimeter calculation)
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int length;
cout << "Please enter the rectangle's length: ";
cin >> length;
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int width;
cout << "Please enter the rectangle's width: ";
cin >> width;
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int perimeter = 2 * (length + width);
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Step 4: Compute the area of the rectangle
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Step 5: Output the results of this computation to the screen.
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Design (area and perimeter calculation)
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int length;
cout << "Please enter the rectangle's length: ";
cin >> length;
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int width;
cout << "Please enter the rectangle's width: ";
cin >> width;
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int perimeter = 2 * (length + width);
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int area = length * width;
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Step 5: Output the results of this computation to the screen.
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Design (area and perimeter calculation)
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int length;
cout << "Please enter the rectangle's length: ";
cin >> length;
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int width;
cout << "Please enter the rectangle's width: ";
cin >> width;
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int perimeter = 2 * (length + width);
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int area = length * width;
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Step 5: Output the results of this computation to the screen.
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Design (area and perimeter calculation)
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int length;
cout << "Please enter the rectangle's length: ";
cin >> length;
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int width;
cout << "Please enter the rectangle's width: ";
cin >> width;
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int perimeter = 2 * (length + width);
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int area = length * width;
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cout << "The perimeter of the rectangle is " << perimeter << endl;
cout << "The area of the rectangle is " << area << endl;
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Write program to compute the perimeter and area of a rectangle. The size of the
rectangle will be specified by the user.
#include <iostream>
using namespace std;
int main() {
int length;
cout << "Please enter the rectangle's length: ";
cin >> length;
int width;
cout << "Please enter the rectangle's width: ";
cin >> width;
int perimeter = 2 * (length + width);
int area = length * width;
cout << "The perimeter of the rectangle is " << perimeter << endl;
cout << "The area of the rectangle is " << area << endl;
return 0;
}
To summarize, an algorithm
refers to the process, not
just the code
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Abstraction
expressing a concept in a more general
form
 related to level of detail
 the higher the abstraction, the less details
are considered
 common in computer science/algorithms
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Abstraction - Example
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consider our chocolate cake example
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Step 1:
Step 2:
Step 3:
Step 4:
Step 5:
Step 6:
Melt chocolate and butter
Stir sugar into melted chocolate
Mix in flour
Spread mix in greased pan.
Bake at 350F for 40 minutes
Cool in pan
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Abstraction – Less (More Detail)
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consider our chocolate cake example
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Step 1:
Step 2:
Step 3:
Step 4:
Step 5:
Step 6:
Melt chocolate and butter
Stir sugar into melted chocolate
Mix in flour
Spread mix in greased pan.
Bake at 350F for 40 minutes
Cool in pan
Step 1a:
Step 1b:
Step 1c:
Step 1d:
Place chocolate in pan
Place butter in pan
Apply blowtorch
Repeat Step 1d until soft
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Abstraction – More (Less Detail)
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consider our chocolate cake example
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Step 1:
Step 2:
Step 3:
Step 4:
Step 5:
Step 6:
Melt chocolate and butter
Stir sugar into melted chocolate
Mix in flour
Spread mix in greased pan.
Bake at 350F for 40 minutes
Cool in pan
Step 1: Combine ingredients
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Abstraction – Examples
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in computer algorithms
High Abstraction
Less Abstraction
Step 1: Load file
Step 2: Convert all a's to @'s
Step 3: Save file
Step 1:
Step 2:
Step 3:
Step 4:
Open Windows Explorer
Double click on required file
Click Ctrl-F
....
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Abstraction – Why?
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in computer programs, there is usually a lot going on
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some details are not important in certain contexts
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saving a file can be described without discussing individual bits,
hard drive sectors, etc ...
complete details can be overwhelming
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billions of instructions executing
I/O read/writes
etc ...
imagine trying to describe saving a file at a hardware level
the right amout of abstraction depends on situation
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electrical engineer: very low level of abstraction
tech support: very high level of abstraction