What’s a Computer? Analog, Digital does it matter? Technically there are two categories of computers, analog or digital. Designs reflect two different.

What’s a Computer?Analog, Digital does it matter?

• 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


• Analog device – operates with measurements that are continuous such a voltage, temperature and rotation.– Speedometer in your car– Traditional thermometer– Classic clock

• An Analog computer uses analog measurements in it’s calculations. Analog measurements are “physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved.” (http://en.wikipedia.org/wiki/Analog_computer)

– Very fast– Somewhat inaccurate– Difficult to replicate results, can you spin a wheel at exactly the same

rate twice in a row?



• This device is a Harmonium. It is a mechanical, analog computer designed analyze sine waves used

in Fournier Analysis.


• Digital Computer – – Information is represented by counting– This is what we think of as a computer. – All information used by the machine is in one of two

states ON (1) or Off (0).• Things we can count include:

– Change from a dollar– Number of students registered in CSE 111– Tuition in dollars

• Highly flexible• Easy to replicate



• Moving from Analog to Digital• Digital Age

– Clock• Hands moving in a circle digits on a screen

– Telephone• 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• Pictures as a series of light waves pictures as a pattern of dots

(pixels).

• It is all about speed and ability to replicate results


What’s a Computer?The Binary Machine

• Computers “speak” a very simple language– 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.



• Computers use Binary – (0,1)– Base 2

• People do not – we use Decimal – (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– Translate them into 0s and 1s– Do whatever they do – “Magic”– Give us the results in a way human understand



• In decimal every number is represented as the digits 0-9

• In binary every number is represented as the digits 0-1

– Decimal to Binary conversion Decimal Binary

- 0 - 0000- 1 - 0001- 2 - 0010- 3 - 0011- 4 - 0100- 5 - 0101- 6 - 0110- 7 - 0111- 8 - 1000- 9 - 1001



• For people in the know –- 0 - 0000- 1 - 0001- 2 - 0010

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• BIT for Binary Digit -- each 0 or 1 in the binary system – Single bit is not overly useful

• BYTE – a group of bits (usually 8)– Each byte represents one character of data

• 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.– Early computers – Apple II – 8 bit Words– Modern machines – can process up to 64 bits/word



• Computers are described by amount of processing memory they contain– Usually described in terms of bytes (K ~ 1000 bytes)

• 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– Earn 100K

– House is priced at 450K


What’s a computer?

• For many a computer is a “black box”!

– Incredible machine that works mysteriously

– How is of little consequence.

– Magic?


What’s a computer?Basic parts

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Central Processing Unit

Input

Memory

Brains

Input & Output

Input & OutputOutput


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What’s a computer?Basic parts

• Every computer is made up of the following components:

– A Central Processing Unit• Arithmetic & Logic Unit

• Control Unit

– Memory• Primary Memory (Usually called RAM)

• Secondary Memory or Mass Storage (Disk drives)

– Input and Output Devices


What’s a computer?Processing Unit

Brains of the Machine

• Central Processing Unit --– Arithmetic and Logic Unit (ALU)

– Control Unit

• Associated Primary Memory

Working together these are the core or any computer.

Size doesn’t matter!


What’s a computer?Central Processing Unit

• Arithmetic & Logic Unit

– As the name implies performs two functions:– Arithmetic

• Responsible for performing the arithmetic operations of addition, subtraction, multiplication and division

– Logic

• Makes simple “decisions” by comparing alternatives and choosing between them

– Less than, greater than, equal to

– AND, OR and NOT


What’s a computer?Control Unit

• The arithmetic and logic unit is responsible for mathematical calculations and comparisons.

• The Control Unit is the computer’s internal coordinator– Traffic Cop– Sends out electronic signals directing the computer to perform

specific tasks such as:• Move data between memory and the CPU• Activating the ALU• Receiving data• Sending information to an output device

– The control unit manages the flow of data throughout the machine based on the instructions it receives from programs.


Using BinaryCoding Information

Remember Bit = 0 or 1, Binary Digit Byte = the number of bits used to represent letters,

numbers and special characters such as $ # , / &. Word = number of bytes a computer can process at

one time by the CPU.

So,

Bits form Bytes and Bytes form Words.



Two common formats for coding letters, numbers and special characters are: ASCII -- American Standard Code for Information Interchange

7 bit code Originally used on non-IBM systems Basis of most currently used systems

EBCDIC -- Extended Binary Coded Decimal Interchange Code 8 bit code Originally used in IBM mainframes

ASCII exists NOT because it makes more sense (which it does) but because it was an economic necessity.



Coding in EBCDIC and ASCII:Letters

We know certain facts about lettersThey have an implied orderingThis ordering must be maintained when letters are translated

into 0’s and 1’s inside the computer

NumbersNumbers clearly have a mathematical orderNumerical ordering must also be maintained when represented

as 0’s and 1’s inside the computer


http://EBCDIC.ASCII.Letters.pdf/

http://EBCDIC.ASCII.Numbers.pdf/


Codes are organized so that mathematics makes sense They are ordered so that each subsequent number is larger than the

one before.

7 > 5

In ASCII 011 0111 > 011 0101

In EBCDIC 1111 0111 > 1111 0110



Codes are designed so that the ordering of English letters makes sense.

A B C D E F … U V W X Y Z Over time we consider this ordering to be fixed The implication is that we can compare letters and that certain

letters appear before others in the alphabet. For Example: A < F and X > F ASCII and EBCDIC code letters so that this concept remains

valid.



Codes are designed so that the ordering of English letters makes sense.

A < F

In ASCII 100 0001 < 100 0110

In EBCDIC 1100 0001 < 1100 0110

X > F

In ASCII 101 1000 > 100 0110

In EBCDIC 1110 0111 > 1100 0110



Codes are designed so that the ordering of English letters makes sense. At the time of its creation, it was argued that ASCII was a more

rational coding scheme based on the way it codes letters.

Both ASCII and EBCDIC are limiting Both can code all of English and most Romance languages. As computer use has expanded both became incomplete ASCII is still the foundation for text based email on most computers

UNICODE Designed to provide a single coding system for every character in

every natural language The Internet uses UNICODE



Error CheckingTransmission errors are a fact of computer lifeThink of the game of TelephonePower interruptions happenLife happensGIGO

What can be done to reduce or repair errors in transmitted characters?



Parity – In common English, Parity means two things are equal.

How could this be applied to error checking?

With computers it applies to a special bit added to each byte before it is transmitted to another computer to allow the receiving machine to check on the accuracy of the transmission.



Odd Parity Look at byte, attach either a 0 or a 1 to force the byte

to be odd Examine the byte coded to mean Z

In ASCII 101 1010Count the number of 1s, there are 4, 4 is even, the parity

bit is set to one (1) to make the string of bits odd.

The byte is coded 1 101 1010EBCDIC does it similarly, by adding a digit at the end.


What’s a Computer? Analog, Digital does it matter? Technically there are two categories of computers, analog or digital. Designs reflect two different.

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