← Text Compression (You Can Say That Again!)
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Text Compression (You Can Say That Again!)
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You Can Say That Again! — Text Compression
| Front | Back |
|---|---|
| What is compression? | Coding data before it is stored, and decoding it when it is retrieved, so the computer can store more data or send it faster. |
| Why do computers need to compress data? | Computers have a limited amount of storage space and need to represent information as efficiently as possible. |
| What are the benefits of compressing data before sending it over the Internet? | Files take up less storage space and download or transmit faster through a modem connection. |
| In the "You Can Say That Again!" puzzle, what do arrows and boxes represent? | Repeated groups of letters, words, or phrases that have already occurred earlier in the text, so they don't need to be written out again. |
| Which direction must arrows always point in the puzzle? | Arrows must always point to an earlier part of the text (decoded left to right and top to bottom, like normal reading). |
| In "Extra for Experts," what does Ban(2,3) mean when decoding "Banana"? | "2" means count back two characters to find the starting point for copying, and "3" means copy three consecutive characters from there. |
| Why are usually only groups of two or more letters worth compressing? | Because coding uses two numbers, so compressing just one letter could make the file bigger instead of smaller. |
| What is Ziv-Lempel coding (LZ coding)? | A compression method based on pointing to earlier occurrences of chunks of text; invented by two Israeli professors in the 1970s. |
| What common computer term is Ziv-Lempel coding related to? | It is sometimes referred to as 'zip' on personal computers, and is also used for 'GIF' images and high-speed modems. |
| How much can LZ coding reduce data size? | It can easily halve the size of the data being compressed. |
| What is another method of compression based on letter frequency? | Giving letters that are used more often shorter codes than the others — an idea used in Morse code. |
| How much has computer storage capacity grown in the last 25 years (as of the resource)? | About a millionfold. |
| Why is compression still needed even though storage capacity has grown so much? | We keep finding more to store (books, libraries, music, movies), and want smaller devices like cellphones and wristwatches to hold lots of information. |
| In the "Short and Sweet" activity, what should students cross out? | All groups of two or more letters that have already occurred earlier in the text, since these could be replaced by a pointer. |
| How does modem compression help data transmission? | It reduces the amount of data that needs to be transmitted over the phone line, so it goes much faster. |
| What is the goal when designing your own compression puzzle? | To see how few of the original words you need to keep while still allowing correct decoding. |
| What happens on computers when text is compressed and later needed? | The computer automatically decompresses (decodes) the data so users just notice more storage space or faster web page display. |
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