Acknowledgement Jeremy Gow jennifer george 1 Last Week Lecture - PDF document

FY04: Introduction to the use of computers jennifer george Acknowledgement  Jeremy Gow jennifer george 1

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 jennifer george Last week’s Lab  Linux Server  PuTTY  SSH  VNC  emacs jennifer george 2

jennifer george Today  Measuring digital data  Bits  Bytes  Kilobytes  Megabytes  ...  SI and Binary units jennifer george 3

More for today  Binary files  Hexadecimal  Text files  Character sets  Text encodings  ASCII, Unicode jennifer george The Analogue World  Information is continuous (smoothly, without breaks) jennifer george 4

The Digital World  Information is discontinuous (broken into chunks)  Modern computing is digital (not analogue) jennifer george 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 jennifer george 5

Everything digital is made of bits jennifer george 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) jennifer george 6

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 jennifer george Binar ary: y: Powers s of 2  Binary based on powers of 2  117 = 2 6 + 2 5 + 2 4 + 2 2 + 2 0  A full byte is (2 8 - 1) = 2 7 + 2 6 + 2 5 + 2 4 + 2 3 + 2 2 + 2 1 + 2 0 jennifer george 7

Group oup 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) jennifer george The Kilobyte (kB)  1000 bytes  8000 bits  Half a page of text  A small icon  About 7 magnetic swipe cards jennifer george 8

The Megabyte (MB)  One millon bytes (1,000,000 = 10 6 )  1000 kilobytes  A thick book  A minute of MP3 (128 kb/s)  6 sec of CD audio  A digital photo (a few MB) jennifer george The Gigabyte (GB)  One billion bytes (1,000,000,000 = 10 9 )  1000 megabytes  TV quality film (a few GB)  17 hours of MP3 (128kb/s)  English Wikipedia (2.7 GB)  The Human Genome (3 GB) jennifer george 9

The Terabyte (TB)  One trillion bytes (1,000,000,000,000 = 10 12 )  1000 gigabytes  Library of Congress (20TB of text)  YouTube (600 TB in 2006) jennifer george The Petabyte (PB)  One quadrillion bytes (1,000,000,000,000,000 = 10 15 )  1000 terabytes  Large Hadron Collider (15  PB/year)  Google storage (??? PB)  All printed material (200 PB) jennifer george 10

Beyond the Petabyte  Exabyte (10 18 )  A year of US telephone calls (9.25 EB)  Zettabyte (10 21 )  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 (10 24 )  The internet? jennifer george 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 jennifer george 11

SI Prefixes  Le Système International d'Unités  Many uses: kilobits, kilobytes, kilometres, ...  1 kilobyte = 1000 bytes jennifer george Binary Prefixes  Based on powers of 2 (like binary)  Used for data only  More convenient when using binary addresses  1 kilobyte = 1024 bytes jennifer george 12

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 jennifer george IEC Binary Prefixes  Attempt in 1999 to resolve ambiguity  Rename binary prefixes (for bytes only)  kilobyte becomes kibibyte jennifer george 13

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) jennifer george 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 jennifer george 14

Hexadecimal Binar ary y for human ans  Binary is hard for people to read & write  Can translate to hexadecimal (base-16)  01111010 →7A jennifer george 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 jennifer george 15

Hexadecimal Example ple jennifer george 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 jennifer george 16

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) jennifer george ASCII Enco coding ding  A character is a single byte  Printing characters... jennifer george 17

ASCII Example ple jennifer george 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.) jennifer george 18

Un Unicode de http://unicode.org/charts/ jennifer george Unicode Latin tin ch charact racter ers jennifer george 19

Unicode Arabi abic c ch charac racter ers jennifer george Unicode CJK K ch charac racter ers jennifer george 20

Unicode Georgia orgian n ch charact racter ers jennifer george Unicode Choic oice 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 jennifer george 21

Text encoding Example ple  Encode the string “£4 = €5” jennifer george 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 jennifer george 22

Group activity Your name in binary (ASCII encoding) jennifer george 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 jennifer george 23

Reading  http://en.wikipedia.org/wiki/Orders_of_m agnitude_(data)  http://en.wikipedia.org/wiki/Binary_prefix jennifer george 24