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2. 4 File size can be a big deal Like when you want more music on your phone Or work on your USB stick Or when you email large files Compression helps with this It means reducing file sizes That means less data to store & send

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4. 4 Not everyone really understands words like ‘bit’ & ‘byte’ So to get your head around these concepts, it helps to know a bit more about how computers work So first we’ll do some background activities that will also help with other topics later in this unit Then we’ll look more closely at this topic for the BTEC exam

5. Online Documents – File Compression 4 Computers use electricity So all those chips & circuits flow with electric current And the current can either be on or off Computer scientists represent this using 1s & 0s, where 1 means on & 0 means off Everything a computer does can be represented with those 1s and 0s Using just those two digits is called binary

6. Online Documents – File Compression 4 What are they called? What are they for? Discuss with your partner

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8. 4

9. 4 How many of a processor’s on/off switches could fit on the head of a pin? 100 million

10. Online Documents – File Compression 4 How many times per second can the circuits switch on/off in a processor? How many years it take you to flick a switch on/off that many times? 100 billion 2,000

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12. 4 Process InputOutput Process InputOutput Process InputOutput

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14. 4

15. 4 Sends email Gets email Email servers Client device

16. Online Documents – File Compression 4 Error – sorry! All the files could not be attached because adding them would cause the message to exceed the maximum size limit of 26 MB Error – sorry! All the files could not be attached because adding them would cause the message to exceed the maximum size limit of 26 MB

17. Online Documents – File Compression 4 So compression means reducing data Reducing the amount of data means less to store & send We now know that computers handle all that data in binary But how do computers actually turn everything into binary? Let’s do a quick activity to see how this basically works using text…

18. Online Documents – File Compression 4 One bit means a single 1 or a single 0. But one bit can’t represent much. So they are grouped in a batch of eight bits called a byte. One byte is just enough to represent one of character, such as a letter, or a number or a punctuation symbol. One way of representing all letters, numbers & symbols on a keyboard is to use a special code called ASCII.

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21. 4 Doing three simple words in binary was hard enough! But imagine how binary data there is to stored in an essay, or send in an email So let’s now look at how a computer can compress the amount of data needed to store or send text Doing this in binary would be tough! So we’ll use an example in English…

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23. 4 Index Word/LettersWhere occur 123 456789... 56 77 168 227 68 24 91 36 swallowed 24, 56, 77, 168, 227 bird 36, 68, 91

24. Online Documents – File Compression 4 So to compress that text, we used a specific method Our method was to cut repeating words That meant less text to store or send But our method also included making an index to store the position of each word that was cut So later, the index can be used to piece the original text back together

25. Online Documents – File Compression 4 The technical term for that kind of method is an algorithm And there are many different algorithms for compressing different kinds of files So we’ll now have a quick look at compressing images, audio, video and documents…

26. Online Documents – File Compression 4 BEFORE File type: File size : PNG 10.6 MB AFTER File type: File size: JPEG 520 KB

27. Online Documents – File Compression 4 BEFORE File type: File size : WAV 32.1 MB AFTER File type: File size: MP3 5.82 MB

28. Online Documents – File Compression 4 BEFORE File type: File size : AVI 10.5 MB AFTER File type: File size: MP4 8.59 MB

29. Online Documents – File Compression 4 So a good way to compress these files was to change the file type BEFOREAFTER PNGJPEG WAVMP3 AVIMP4 High Quality = More Data Less Data = Lower Quality

30. Online Documents – File Compression 4 Our final example uses documents Folders of docs can be compressed using a method called zipping.. BEFORE Folder size : 5.04 MB AFTER 4.7 MB Folder size :

31. Online Documents – File Compression 4 So the multiple docs were ‘zipped’ That puts them into one zipped folder It reduced the overall folder size And for email, one zipped folder is far easier to attach than multiple docs And zipping also compresses the folder size So email will be quicker to download And receiver can ‘unzip’ the files ‘Zip’ is very popular But other similar methods include rar & 7z

32. Online Documents – File Compression 4 Zip folder before attach Unzip docs when open

33. Online Documents – File Compression 4 Now let’s focus on what you need to know for the BTEC exam…

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