Difficulty: Easy
Correct Answer: Lossless
Explanation:
Introduction / Context:
ZIP files are a common way to compress and package multiple files into a single archive, making them easier to store and transfer. The type of compression used affects whether the original data can be recovered exactly or only approximately. For many types of files, such as documents, programs, and source code, it is essential that no information is lost during compression. This question asks you to identify whether ZIP files use lossless or lossy data compression.
Given Data / Assumptions:
Concept / Approach:
ZIP is a lossless compression format. It uses algorithms such as DEFLATE to reduce file size while preserving all original information. When you decompress a ZIP archive, the resulting files are bit for bit identical to the originals. Lossy compression, in contrast, is used in formats like JPEG for images or MP3 for audio, where some data is removed to achieve higher compression at the cost of some quality. Because ZIP is intended for generic files where data loss would be unacceptable, it uses lossless compression and does not discard any information. Therefore, the correct answer is lossless compression.
Step-by-Step Solution:
Step 1: Recall what happens when you compress and then extract a ZIP file.
The extracted files match the original files exactly; they can be checksummed to verify this.
Step 2: Match this behaviour to the definition of lossless compression.
Lossless means no data is lost and the original can be reconstructed perfectly.
Step 3: Consider lossy compression.
Lossy formats, such as JPEG and MP3, intentionally discard some data that is less noticeable to reduce size.
Step 4: Check whether ZIP ever discards data.
ZIP archives are designed to be reversible; they keep all bits needed to reconstruct files exactly.
Step 5: Conclude that ZIP uses lossless compression.
Verification / Alternative check:
Technical documentation for the ZIP format explains that it uses lossless compression algorithms like DEFLATE, which apply techniques such as Huffman coding and LZ77 style back references. These algorithms compress data by exploiting patterns but preserve complete information so that decompression can rebuild the exact original stream. Archive utilities like WinZip, 7 Zip, and built in ZIP support in operating systems all emphasise that ZIP compression does not degrade file content. If ZIP were lossy, executable files and documents would be corrupted after extraction, which clearly does not happen. This confirms that ZIP uses lossless compression.
Why Other Options Are Wrong:
Option B (Lossy): Lossy compression would alter the data and is used for media formats where some quality loss is acceptable, not for ZIP archives.
Option C (Any of the above): ZIP does not switch between lossy and lossless; it is strictly a lossless archive format.
Option D (None of the above): Incorrect because lossless is a standard term that precisely describes the type of compression used by ZIP.
Common Pitfalls:
Some learners associate compression with lossy techniques because they are familiar with JPEG images or MP3 audio, both of which reduce file size by discarding information. They may not realise that many compression schemes are fully reversible. Another confusion arises from thinking that higher compression ratios always imply lossy methods; however, lossless algorithms can often achieve significant savings on text or executable files. To avoid mistakes, remember that portable archive formats like ZIP and gzip are lossless, whereas multimedia codecs like JPEG and MP3 are typically lossy.
Final Answer:
ZIP files use lossless compression, allowing original data to be recovered exactly when the archive is extracted.
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