Compression techniques play a crucial role in modern computing, allowing users to reduce file sizes for efficient storage, transmission, and archival purposes. Among the plethora of compression tools available, three popular formats stand out: tar, gzip, and zip. While they serve similar purposes, each has its unique features and applications. This article aims to elucidate the differences between tar, gzip, and zip, exploring their functionalities, compression methods, and common use cases.
Understanding Tar, Gzip, and Zip
Before delving into the differences, let’s briefly overview each compression format:
Tar (Tape Archive)
---
Tar is not a compression algorithm per se but rather a file archiving tool commonly used in Unix-like operating systems. It bundles multiple files and directories into a single archive file without compressing them. Tar archives are often combined with compression utilities like gzip to create compressed tarballs.
Random access to individual files is not possible with tar, because the archive files do not have a directory that holds the file offsets for quick access, as is the case with Zip (this does not mean that individual files cannot be extracted from an archive). However, the omission of this additional structure also makes it possible to easily enlarge archives and, above all, to extract files from incomplete or defective archives.
Today, tar archives are more often found in tar files than on tapes. These archive files are usually compressed to reduce their size. For this purpose, Unix-typical packing programs such as compress, gzip, bzip2, xz or lzma are usually used. The approach of first attaching all files uncompressed to each other in order to compress them is called solid compression and is now also used for other archive formats such as RAR or 7-Zip. Depending on the compression program used, the file extensions of a tarball are usually .tar.Z, .tar.gz or short .tgz (gzip), .tar.bz2 or .tbz2 or .tbz (bzip2) or .tar.xz or .txz (xz), or .tar.lzma (lzma).
If solid compression is not desired, the individual files can also be compressed first and then integrated into the tarball. This means that it is still possible to unpack incomplete parts of a tar archive if an algorithm for solid compression has been chosen, which does not support resetting after a defective block. However, the disadvantages (limited file size due to the necessary temporary space for compressing individual files, or complete failure of files that change during archiving) outweigh the disadvantages, so that this approach is usually not chosen. In addition, the compression rate is usually lower than with solid compression, which also includes the attributes of the file in the compression. In addition, there is only a slight speed advantage when unpacking individual files, as the archive has to be searched sequentially anyway.
Unlike zip archives, a tar file does not contain a table of contents. Software that wants to process a tar archive must always read the entire file in order to know what is in it. Only then can the software extract the desired part of the archive. With the update option, new or changed files are appended to the back of the tar archive (and old or deleted files are kept in the same place), which is technically the simplest solution, but makes the problem of the missing table of contents even worse. These drawbacks stem from the fact that tar was originally designed to back up data to tape drives.
Gzip (GNU zip)
Gzip is a compression utility designed to reduce the size of individual files using the DEFLATE compression algorithm. It is widely used on Unix-like systems to compress single files or combine with tar to create compressed tarballs (.tar.gz or .tgz files). Gzip achieves high compression ratios while maintaining relatively fast compression and decompression speeds.
gzip is based on the Deflate algorithm, which is a combination of LZ77 and Huffman encoding. Deflate was developed in response to the patents that insisted on LZW and other compression algorithms. The ZIP file format also mainly uses Deflate for compression, but otherwise should not be confused with gzip.
Zip
Zip is a popular compression and archiving format commonly used in Windows and other platforms. Unlike tar, which archives files without compression, zip combines archiving and compression into a single step. It employs various compression algorithms, including DEFLATE, LZMA, and BZIP2, to reduce file sizes. Zip archives (.zip files) can contain multiple files and directories, making them suitable for storing and sharing collections of files.
The ZIP format is first of all a data container in which several files can be stored compressed or uncompressed and can also be decompressed (extracted) individually. In addition, the format also allows you to save the corresponding storage location path. It is also possible to encrypt the otherwise only compressed files with a password.
The ZIP format does not support progressive compression (also called solid), the files are compressed individually. On the one hand, this allows for flexible handling (delete/add files from the archive without having to recompress everything; extraction of individual files without having to decompress previous files), but has the disadvantage that redundancies between the files cannot be taken into account during compression. This disadvantage can be circumvented by first archiving the files uncompressed and saving the resulting zip file in another compressed form (usually only useful for a large number of similar files).
The files are stored as file entries in any order. The file entries all start with a local header that describes the file entry and introduces the data section with the effective contents. In order to ensure the handling of these arbitrarily arranged entries, there is a central directory at the end of the zip file, which references all file entries based on the local file headers. The order of the file entries and the corresponding references in the central directory may differ from each other. It is therefore a non-sequential structure that can best be described with the concept of random access.
On the other hand, this non-sequential format also means that, in contrast to the tar format, which has been common since 1977 and standardized since 1988, incomplete archives or archives that are defective in the back cannot be unpacked at all.
Differences Between Tar, Gzip, and Zip
Now, let’s explore the key differences between tar, gzip, and zip:
Compression Method:
Tar does not perform compression on its own. It simply archives multiple files and directories into a single file without compression.
Gzip employs the DEFLATE compression algorithm to compress individual files. It produces files with the .gz extension.
Zip combines file archiving and compression using various algorithms like DEFLATE, LZMA, and BZIP2. Zip archives have the .zip extension.
Usage and Compatibility:
Tar is primarily used in Unix-like systems for creating archive files, often combined with gzip for compression. It is less common in Windows environments.
Gzip is widely used on Unix-like systems for compressing individual files or combining with tar for creating compressed tarballs. It is less prevalent in Windows but can be installed and used.
Zip is ubiquitous across multiple platforms, including Windows, macOS, and Unix-like systems. It is commonly used for creating compressed archives that are compatible across different operating systems.
Archive Structure:
Tar archives preserve the directory structure of the files being archived. They do not compress files by default, resulting in larger archive sizes.
Gzip compresses individual files, preserving their original names and attributes. It does not maintain directory structure.
Zip archives can contain multiple files and directories, preserving their relative paths within the archive. It compresses files and directories while retaining their original structure.
Compression Ratio and Speed:
Since tar does not perform compression, it does not achieve compression ratios. Archiving with tar is relatively fast.
Gzip offers high compression ratios, especially for text-based files, at the cost of slightly slower compression and decompression speeds.
Zip supports multiple compression algorithms, with varying compression ratios and speeds depending on the chosen algorithm. It generally provides a balance between compression efficiency and speed.
Common Use Cases
Tar: Creating uncompressed archive files, combining with gzip for creating compressed tarballs, and transferring or archiving directories and files in Unix-like environments. For example, backup of WordPress SQL database.
Gzip: Compressing individual files, creating compressed tarballs with tar, reducing file sizes for efficient storage and transmission.
Zip: Creating compressed archives compatible with multiple platforms, sharing files over the internet, packaging software distributions, and creating backups. For example, backup of WordPress FTP content.
Conclusion
Tar, gzip, and zip are versatile compression tools with distinct functionalities and applications. While tar focuses on archiving files without compression, gzip and zip excel in compressing individual files or collections of files into smaller, more manageable packages. Understanding the differences between these compression formats enables users to choose the most suitable tool for their specific needs, whether it’s efficient storage, fast transmission, or cross-platform compatibility.
