Transcript Intro to computers

Lecture 1: Intro to Computers
Yoni Fridman
6/28/01
Outline
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What are computers?
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What is programming?
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Real-world algorithms
Computer algorithms
Storing data
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Hardware
Software
Decimal vs. binary
Variables
Programming languages
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Executing a program
What Are Computers?
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Computers are “information processors.”
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Computers are made up of hardware…
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They take in information – from the keyboard, from a mouse,
through an electronic “eye,” etc.
They do something with the information (i.e., process it).
Then they spit out the results – through the monitor, by moving a
robotic arm, etc.
The tangible parts of a computer.
Monitor, mouse, memory cards, etc.
And software.
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The programs that tell the computer what to do.
Word processor, video games, etc.
Hardware
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Processors – the “brains” of the computer.
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Memory – the ability to store information.
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CPU (central processing unit), graphics processors, math
processors.
Main memory, or RAM, stores information while the computer is
on.
Secondary memory (hard drive, floppy disk, etc.) stores
information indefinitely.
Peripheral devices – provide an interface to the
outside world.
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Input devices – mouse, keyboard.
Output devices – Monitor, printer.
Hardware
Output
Input
CPU
Main Memory
Secondary
Memory
Software
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Tells the hardware what to do.
Operating Systems (OS)
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Collection of programs that interact directly with the hardware.
DOS, Windows, MacOS, Unix, Linux.
Applications
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A program not involved in the OS that performs a particular task.
Word processor, drawing application, web browser, video game.
Anything written by you in Java.
Software
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An OS acts as a bridge between applications and
hardware.
An application sends a request to the OS, which
then tells the hardware what to do.
OS
Hardware
Software
Application
What Is Programming?
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Programming is entering a series of commands,
or instructions, that tell the computer what to do.
The instructions must:
1.
2.
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Be discrete, i.e., not overlap or blend together.
Be precisely defined, not vague or ambiguous.
These instructions combine to form an algorithm.
The process of designing and writing an
algorithm is called programming.
Real-World Algorithms
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Algorithms exist in the real world, and they’re
written in natural languages (e.g., English).
For example, a recipe in a cookbook or
instructions for a board game.
But, natural language algorithms lack the precision
needed for a computer to understand.
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For example, “stir until thick.”
A computer can’t make
judgments, and needs
perfectly precise instructions.
Computer Algorithms
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Computer algorithms are written in programming
languages (e.g., Java).
Such algorithms are precise enough for the
computer – they require no judgment.
Example: Compute the remainder of 23/7.
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Subtract 7 from 23.
If the result is less than 7, then that’s your answer. Stop.
Otherwise, subtract 7 from the result.
Go back to step 2.
Storing Data
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Data refers to information that can be stored, for
example, numbers, letters, or names.
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1, 23, 10.75, x, hello, Tom
All computers really do is manipulate data.
This data must be stored in the computer – how?
Decimal vs. Binary
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We usually think of numbers in decimal (0-9).
Computers only know binary (0 and 1).
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Binary is longer, but it’s the only way computers
can store info.
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Example: 25 in decimal equals 11001 in binary.
Not only numbers, but also letters and all other data are stored in
the computer in binary.
One binary digit is called a bit.
A bit can’t store much, so computers group 8 bits
together into what is called a byte – like a word.
Variables
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Variables are locations within an algorithm that
store data.
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Remember our example: Remainder of 23/7.
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For example, the variables x and y are usually used to store
coordinates in 2D.
Subtract 7 from 23.
If the result is less than 7, then that’s your answer. Stop.
Otherwise, subtract 7 from the result.
Go back to step 2.
This algorithm would contain three variables –
one for “7”, one for “23”, and one for the result.
Programming Languages
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Machine languages manipulate data in a very
basic, primitive way.
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They’re composed of bits, and almost impossible to understand.
Assembly languages are composed of commands
rather than bits, but still difficult to understand.
High-level languages are much more similar to
English.
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Programmers write using high-level languages, and the computer
translates these to an assembly language and then to a machine
language.
Examples: Java, C++, BASIC, FORTRAN, and Pascal.
Executing a Program
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The text of a program written in Java, for
example, is called source code.
The computer can’t directly understand source
code – it’s not executable.
There are two methods to execute a program:
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Compile it: A compiler first makes sure that the source code
obeys the rules of the programming language. It then translates
the source code to machine language and stores this in a file. This
file can now be executed.
Interpret it: An interpreter executes the machine instructions
corresponding to the source code.
Homework
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Go to the campus store and buy the textbook and
three floppy disks.
Read:
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Sections 1.1, 1.3, 1.4, and 1.5 to review today’s lecture.
Sections 2.1, 2.4, 2.5, 2.6, 2.7, and 2.8 for tomorrow’s lecture.
HW1 out today, due Monday.
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Written part: Write a precise real-world algorithm to light a match.
Programming part: Getting started with Visual J++.