Computer Science E-1: Understanding Computers and the
Internet
Harvard University Extension School
Fall 2005
Lecture 1: Hardware
Wooly Willy and Floppy Disks
Inside of a floppy disk are particles not unlike the particles
used with the Wooly Willy toy. Since the disk stores data in
binary numbers (0 and 1) that can be done with the particles on
the film in a floppy disk by magnetizing them. There is a
"reading arm" in a floppy disk drive that reads those magnetized
particles as either 0's or 1's.
Student exercise: playing with floppies
Floppy disks tend to hold about 1.44 megabytes of data. Hard
drives, by contrast hold gigabytes of data.
How does a computer compute?
Counting
Counting on your fingers
Counting with an abacus
Counting in binary
256 128 64 32
16 8 4 2
1
Might use negatively charged particles to represent a "0"
Might use positively charged particles to represent a "1"
Can also be represented by "off" and "on"
Bit: binary digit
What is the largest number that can be represented by 8 bits? 255
Student exercise: counting in binary with light bulbs
How does a calculator work?
Stores numbers and function in registers which store electrical
charges
What is the brains of a computer?
Processor
Base-2 representation of numbers
Student exercise: fill in base-2 values of decimal numbers
What about storing characters, words, and graphics?
ASCII (American Standard Code for Information Interchange): A
means for representing characters (such as the english letters A, B,
C, ..., Z) with numbers
Non-English characters are represented with a different system (Unicode).
Student exercise: take a "BOW"
Course Overview
Requirements: Attend or watch all lectures, complete problem
sets, take 2 exams, and produce a final project