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System Software, Application Software and the User Interface

Zipping and archive files

  • 3 things to know
  • AS Unit 2

Overview

Zip file, how zipping shrinks a file and self-extracting archive.

What you need to know

Answer each one before you reveal it.

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Key term

Is zipping lossless or lossy?

Key term

What must be done to a zipped file before a program can work on it?

Key term

How does a zip file preserve a folder structure?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is a zip file?

    Model answer

    A zip file is a single archive file holding one or more compressed files together with a record of their names, sizes and folder structure.

  2. 2

    Is zipping lossless or lossy?

    Model answer

    Zipping is lossless, so every file extracted from a zip is identical to the one that went into it.

  3. 3

    Describe how zipping shrinks a file.

    Model answer

    Zipping scans the file for sequences of bytes that have appeared before and replaces each repeat with a short reference back to the earlier copy, then codes the commonest symbols using the fewest bits.

  4. 4

    What must be done to a zipped file before a program can work on it?

    Model answer

    A zipped file must be extracted first, and extraction rebuilds the original bytes from the stored references before any program can open the file.

  5. 5

    Why is zipping useful when sending several files by email?

    Model answer

    Zipping gathers the files into one attachment and reduces the total size, so a single smaller item is sent instead of many that might exceed a size limit.

  6. 6

    How does a zip file preserve a folder structure?

    Model answer

    A zip file stores the path of each entry alongside it, so extraction recreates the same folders holding the same files.

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