[PDF] - Acknowledgement Jeremy Gow jennifer george 1 Last Week Lecture PDF Document

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FY04: Introduction to the use of computers

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Acknowledgement

 Jeremy Gow

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Last Week Lecture

 Mass storage: hard disks, optical, flash  Huge increases in capacity over years  Filesystems  Files and directories  Unix, OS X and Windows all different  Windows also uses drives  Can be shared over network

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Last week’s Lab

 Linux Server  PuTTY  SSH  VNC  emacs

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Today

 Measuring digital data  Bits  Bytes  Kilobytes  Megabytes  ...  SI and Binary units

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More for today

 Binary files  Hexadecimal  Text files  Character sets  Text encodings  ASCII, Unicode

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The Analogue World

 Information is continuous (smoothly,

without breaks)

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The Digital World

 Information is discontinuous (broken

into chunks)

 Modern computing is digital (not

analogue)

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Bits: The foundation of digital computing

 A bit is smallest possible chunk of

information

 the difference between two possibilities  on/off, up/down, yes/no, heads/tails...  Traditionally 0 or 1 (Binary digIT)  Unit of storage (written b)  Space used to store something as 0s and 1s

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Everything digital is made of bits

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Bytes

 A byte is 8 bits  Written B, so 8b = 1B  Unit of storage  This image is 7395b, about 924B  Related units  nybble: 4 bits (0.5 bytes)  crumb: 2 bits (0.25 bytes)

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Binary: Numbers as bits

 Representing numbers using bits  117 = 64 + 32 + 16 + 4 + 1  A full byte is 255 = 128 + 64 + 32 + 16 +

8 + 4 + 2 + 1

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Binar ary: y: Powers s of 2

 Binary based on powers of 2  117 = 26 + 25 + 24 + 22 + 20  A full byte is (28 - 1) = 27 + 26 + 25 + 24 +

23 + 22 + 21 + 20

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Group

up exercise:

cise: Your ur Age in Binary

 In groups of 4 or 5  Work out your individual ages in

binary

 Work out your combined age in binary  I’m 100001 (tomorrow I’ll be 100010)

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The Kilobyte (kB)

 1000 bytes  8000 bits  Half a page of text  A small icon  About 7 magnetic swipe cards

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The Megabyte (MB)

 One millon bytes (1,000,000 = 106)  1000 kilobytes  A thick book  A minute of MP3 (128 kb/s)  6 sec of CD audio  A digital photo (a few MB)

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The Gigabyte (GB)

 One billion bytes (1,000,000,000 = 109)  1000 megabytes  TV quality film (a few GB)  17 hours of MP3 (128kb/s)  English Wikipedia (2.7 GB)  The Human Genome (3 GB)

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The Terabyte (TB)

 One trillion bytes (1,000,000,000,000 =

1012)

 1000 gigabytes  Library of Congress (20TB of text)  YouTube (600 TB in 2006)

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The Petabyte (PB)

 One quadrillion bytes

(1,000,000,000,000,000 = 1015)

 1000 terabytes  Large Hadron Collider (15  PB/year)  Google storage (??? PB)  All printed material (200 PB)

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Beyond the Petabyte

 Exabyte (1018)  A year of US telephone calls (9.25 EB)  Zettabyte (1021)  All electronic data (1.8 ZB by 2011)  1 gram of DNA (2.25 ZB)  “All words ever spoken” as 32kb/s audio (42

ZB)

 Yottabyte (1024)  The internet?

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Group exercise How much data do you own?

 In groups of 3 or 4  Estimate how much digital data you

each own

 Photos, music etc.  What takes up the most space?  Laptops, iPods, phones...  1 GB = 1000 MB  1 MB = 1000 kB

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SI Prefixes

 Le Système International d'Unités  Many uses: kilobits, kilobytes,

kilometres, ...

 1 kilobyte = 1000 bytes

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Binary Prefixes

 Based on powers of 2 (like binary)  Used for data only  More convenient when using binary

addresses

 1 kilobyte = 1024 bytes

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SI versus Binary

 Each unit now has two different

meanings

 Is a kilobyte 1000 or 1024 bits?  Binary kB 2.4% larger than SI kB

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IEC Binary Prefixes

 Attempt in 1999 to resolve ambiguity  Rename binary prefixes (for bytes only)  kilobyte becomes kibibyte

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Binary files

 Files are zeros and ones (grouped into

bytes)

 Designed to be interpreted in some

way

 Text (bytes → characters)  Image (bytes → pixels)  MP3 files (bytes → sounds)  ...  Each uses a different encoding (stuff

→ bytes)

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Binary: Numbers as bits

 Representing numbers using bits  117 = 64 + 32 + 16 + 4 + 1  A full byte is 255 = 128 + 64 + 32 + 16 +

8 + 4 + 2 + 1

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Hexadecimal Binar ary y for human ans

 Binary is hard for people to read & write  Can translate to hexadecimal (base-16)  01111010 →7A

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Hexadecimal Conver ertin ting g to and d from m binary

 Each hexadigit represents four bits  Two hexadigits is one byte, e.g. 7A →

0111 1010

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Hexadecimal Example ple

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Text files

 Text files contain a sequence of characters

 e.g. emails, web pages, ...

 They are binary files + a text encoding  Encoding defines byte for each character  Encodings may have different character sets

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ASCII Charact aracter er set et

 American Standard Code for

Information Interchange

 128 characters  Printing characters (inc. space)  !”#$%&’()*+,-

./0123456789:;<=>?@ABCDEFGHIJKLMN OPQRSTUVWXYZ[\] ^_`abcdefghijklmnopqrstuvwxyz{|}~

 32 control characters  Tab, line feed, bell, ... (mostly obsolete)

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ASCII Enco coding ding

 A character is a single byte  Printing characters...

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ASCII Example ple

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Unicode Un Univer ersal sal Charact racter er Set et

 Over 100,000 characters  From world and historical scripts  Alphabetic characters  Technical & mathematical symbols  Combination characters (ligatures,

accents)

 Control characters (new line etc.)

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19 Un Unicode de

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http://unicode.org/charts/

Unicode Latin tin ch charact racter ers

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Unicode Arabi abic c ch charac racter ers

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Unicode CJK K ch charac racter ers

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Unicode Georgia

rgian

n ch charact racter ers

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Unicode Choic

ice

e of enco codings dings

 UCS-4 (simple)  4 bytes per character  UTF-16 (e.g. Windows)  Usually 2 bytes, some use 4  UTF-8 (e.g. Unix)  ASCII characters need 1 byte (compatible!)  Others need 2, 3 or 4 bytes

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Text encoding Example ple

 Encode the string “£4 = €5”

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Word processing files

 Word processing applications  Microsoft Word, Open Office Writer, Pages,

Star Office, Abiword, KWord, ...

 Used to represent text, but  large amounts of formatting information  include graphics, charts and more  don’t usually use standard text encoding

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Group activity Your name in binary (ASCII encoding)

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Summary

 Binary files  Hexadecimal makes binary easier to

read

 Text files  = binary file + text encoding  Encodings have different character sets  ASCII and Unicode  Reading: Brookshear §1.4

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