What’s a Computer?
Analog, Digital does it matter?
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Technically there are two categories of
computers, analog or digital.
Designs reflect two different ways to look at or
analyze the world.
Copyright © 2008 by Helene G. Kershner
What’s a Computer?
Analog, Digital does it matter?

Analog device – operates with measurements that are
continuous such a voltage, temperature and rotation.
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Speedometer in your car
Traditional thermometer
Classic clock
Analog computer uses analog measurements in it’s
calculations
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Very fast
Somewhat inaccurate
Difficult to replicate results, can you spin a wheel at exactly the
same rate twice in a row?
Copyright © 2008 by Helene G. Kershner
What’s a Computer?
Analog, Digital does it matter?
Digital Computer –
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Information is represented by counting
This is what we think of as a computer.
All information used by the machine is one of two states
ON (1) or Off (0).
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Change from a dollar
Number of students registered in CSE 111
Tuition in dollars
Highly flexible
Easy to replicate
Copyright © 2008 by Helene G. Kershner
What’s a Computer?
Analog, Digital does it matter?
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Moving from Analog to Digital
Digital Age
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Clock
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Telephone
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10 digits in a circle, distance from beginning was used to
represent the digit  push a button
Voice as a sound wave  voice as a pattern of pulses
Television and Movies
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Hands moving in a circle  digits on a screen
Pictures as a series of light waves  pictures as a pattern of
dots (pixels).
It is all about speed and ability to replicate results
Copyright © 2008 by Helene G. Kershner
What’s a Computer?
The Binary Machine
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Computers “speak” a very simple language
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Two digits – 0 and 1
Don’t really understand the data or instructions they are given
Know how to “follow” them -- circuit path
The 1 state, current is present -- ON
The 0 state, current is absent – OFF
Binary -- The entire language of mathematics can be
converted into a system that just uses 0s and 1s.
Copyright © 2008 by Helene G. Kershner
What’s a Computer?
The Binary Machine
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Computers use Binary
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People do not – we use Decimal
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(0,1)
Base 2
(0,1,2,3,4,5,6,7,8,9)
Base 10
Perhaps this is because we have 10 finger and 10 toes
Modern computers take in decimal number and letters
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Translate them into 0s and 1s
Do whatever they do – “Magic”
Give us the results in a way human understand
Copyright © 2008 by Helene G. Kershner
What’s a Computer?
The Binary Machine
In decimal every number is represented
as the digits 0-9
In binary every number is represented as
the digits 0-1
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Decimal to Binary conversion
DecimalBinary
-0-1-2-3-4-5-6-7-8-9-
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
Copyright © 2008 by Helene G. Kershner
What’s a Computer?
The Binary Machine
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For people in the know –
http://www.thinkgeek.com/tshirts/frustrations/5aa9/zoom/
Copyright © 2008 by Helene G. Kershner
What’s a Computer?
The Binary Machine
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BIT for Binary Digit -- each 0 or 1 in the binary
system
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Single bit is not overly useful
BYTE – a group of bits (usually 8)
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Each byte represents one character of data
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Numbers, letters, special characters (%, $, # etc.)
Letter, numbers and symbols are the form we use to
represent information.
WORD – the number of bits that can be processed at
one time by the central processing unit (the “brain”) of
the computer.
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Early computers – Apple II – 8 bit Words
Modern machines – can process up to 64 bits/word
Copyright © 2008 by Helene G. Kershner
What’s a Computer?
The Binary Machine
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Computers are described by amount of processing
memory they contain
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Usually described in terms of bytes (K ~ 1000 bytes)
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Megabyte or megs [MB]= ~1000K or ~1 million bytes
Gigabyte or gigs [GB] = ~1000MB or ~1 billion bytes
Terabyte = ~1000GB or ~1 trillion bytes
The notation has gained common usage
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Earn 100K
House is priced at 450K
Copyright © 2008 by Helene G. Kershner
What’s a computer?
Basic parts
Input & Output
Input
Central Processing Unit
&
Arithmetic & Logic Unit
Brains
Memory
Input & Output
Output
computer.howstuffworks.com/cd.htm, staples.com, dell.com
Copyright © 2008 by Helene G. Kershner