What is data compression?
The process of encrypting data so it cannot be read
The process of permanently deleting files to free up space
The process of converting analog data into digital data
The process of reducing the number of bits needed to represent data
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What is one benefit of compressing a file before sending it over a network?
It transfers faster because it uses less bandwidth
It guarantees the file can never be corrupted
It removes the need to store the file at all
It automatically improves the quality of the file
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Which statement about lossless compression is correct?
Some data is permanently removed and cannot be recovered
The original data can be perfectly reconstructed from the compressed version
It always reduces file size more than lossy compression
It can only be used on image files
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Which of the following best explains how a lossless algorithm is able to make a file smaller?
By identifying repeated patterns and redundancy and storing them more efficiently
By deleting every second bit in the file
By permanently removing detail the user is unlikely to notice
By converting the file into an encrypted form
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A text file is compressed so that it uses fewer bits than before. Which statement is correct?
Fewer bits always means some of the original meaning has been lost
Fewer bits does not necessarily mean less information; the original meaning can be fully preserved
A file can never be represented with fewer bits than its original size
Reducing the number of bits always corrupts the file
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Which of the following files is most appropriate to compress using a lossless method?
A background music track for a game
A short promotional video clip
A photograph used as a website banner
A spreadsheet containing a company's financial records
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A law firm needs to compress a signed contract for storage, and every character of the text must remain exactly as written. Which type of compression is appropriate, and why?
Lossy, because it produces the smallest possible file
Lossy, because legal text is not affected by small changes
No compression, because text files cannot be compressed
Lossless, because the document must be reconstructed exactly
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Which two of the following are benefits of compressing data? Select two answers.
It reduces the amount of storage space required
It always increases the quality of the original data
It speeds up transmission of the data over a network
It removes the need to ever back up the data
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Which of the following best describes lossy compression?
It rearranges data so the file opens faster but stays the same size
It reduces file size while keeping every detail of the original
It permanently removes some data, producing an approximation that cannot be fully restored
It encrypts the data so only authorised users can open it
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A researcher archives a set of scientific measurements that will be re-analysed later, and every value must remain exactly correct. Which type of compression should be used, and why?
No compression, because compressing any data always corrupts it
Lossy, because it always produces the smallest possible file
Lossy, because scientific data is never affected by small changes
Lossless, because the original data must be reconstructed exactly
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A user wants to email a large video clip and does not mind a small drop in quality so long as it sends quickly. Which type of compression is most appropriate?
Lossy, because it reduces file size significantly and the small quality loss is acceptable
Lossless, because it reduces file size more than lossy compression
Lossless, because video files cannot be compressed with lossy methods
No compression, because the clip must stay exactly as recorded
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Which two factors would most favour choosing lossy over lossless compression? Select two answers.
The data must be reconstructed exactly
The file must be as small as possible
The file is a text document where every character matters
A minor loss of quality will not be noticed by the audience
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Which of the following is not a reason to choose a more aggressive (lossy) compression method?
Storage space is very limited
The data must be able to be reconstructed exactly
The file must transfer quickly over a slow network
The end user is unlikely to notice a small quality difference
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Two files are the same size. File X contains a single word repeated hundreds of times, while File Y contains dense, non-repetitive data. Which file is likely to compress to a smaller size, and why?
File Y, because non-repetitive data always compresses better
Both compress by exactly the same amount regardless of content
File X, because it contains more redundancy that a compression algorithm can exploit
Neither, because files of equal size always compress to equal size
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Compared with lossless compression, lossy compression usually does which of the following?
Reduces file size more, but the original cannot be perfectly reconstructed
Reduces file size less, but preserves every detail of the original
Produces a file identical to the original after decompression
Increases file size while improving quality
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The same image is compressed twice: once with a lossless method and once with a lossy method. After each compressed file is decompressed, which statement is correct?
Both decompressed images are identical to the original
The lossless image is identical to the original, while the lossy image is an approximation
The lossy image is identical to the original, while the lossless image is an approximation
Neither decompressed image resembles the original
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A web designer wants product photos to load quickly on a shopping site and is willing to accept a slight reduction in image quality. Which type of compression best meets these priorities?
Lossless, because it reduces file size more than lossy compression
Lossy, because it significantly reduces file size and the small quality loss is acceptable
Lossless, because images can only be compressed without any loss
No compression, because the photos must stay exactly as taken
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Which two factors would most favour choosing lossless over lossy compression?
Select two answers.
The data must be reconstructed exactly
The file must be made as small as possible, even if quality drops
The file is program source code where every character matters
A minor loss of quality will not be noticed by the audience
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Which statement about lossy compression is false?
Lossy compression produces an approximation of the original data
Lossy compression removes some detail to reduce file size
Lossy compression destroys the entire file so it can no longer be opened
Lossy compression is often used for audio, images, and video
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Which of the following statements about the trade-offs of compression is false?
Lossy compression can usually achieve a greater reduction in file size than lossless compression
Choosing a compression method involves weighing file size against quality
Lossless compression always produces a smaller file than lossy compression
The best compression method depends on the purpose of the data and how it will be used
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