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Differences Between The 5 Types Of Archiving And Compression Formats




  • .7z
  • .7z is a compressed archive file format that supports several different data compression, encryption and pre-processing filters. The .7z format initially appeared as implemented by the 7-Zip archiver. Both the 7-Zip program and a library to read the .7z file format are publicly available under the terms of the GNU Lesser General Public License.

    Features of the .7z format are:

    • Open, modular architecture which allows any compression, conversion, or encryption method to be stacked.
    • Compression ratios from about 2 – 10%
    • Ability to compress large files. Largest is about 16 billion GB.
    • Uses a 16-bit code standard for uniform representation of all the character systems in the world, digits, symbols, and control sequences to use when storing data.
    • Support for solid compression, where multiple files of like type are compressed within a single stream, in order to exploit the combined redundancy inherent in similar files.
    • Even archive headers (supplemental data placed at the beginning of a block of data being stored which contain information for handling the data block) are compressed.
    • AES (Advanced Encryption Standard) 256 bit key encryption is used to encrypt filenames.

  • .tar / .gz
  • .tar (tape archive) is actually an archive format only. What it does is only to collate collections of files into one larger file, for distribution or archiving while preserving file system information such as user and group permissions, dates, and directory structures.

    .gz (GNU zip) on the other hand is used to compress files, with no archiving capabilities whatsoever.

    Both formats are usually used together to compress files resulting in .tar.gz or .tgz. This format is commonly known as tarball. The ‘Content-Encoding’ header in HTTP/1.1 allows clients to optionally receive compressed HTTP responses and to send compressed requests. It saves bandwidth as compression ratios can reach up to about 80%

  • .rar
  • Eugene Roshal developed the .rar format, which stands for Roshal ARchive. .7z’s LZMA algorithm is quite similar to RAR in providing extremely high compression efficiency at the cost of compute time to compress and decompress. Both provide among the highest compression efficiency of any popular scheme, with the question of which algorithm is the more efficient compression scheme strongly depending on the files being compressed.

    Notable features include :

    • Ability to split archives into modular pieces called volumes. This is done efficiently with the built-in support for multi-volume files. It enable the unpacking program to simply prompt the user for the next disk, without any hassle of manually copying and then rejoining the pieces, or for extracting a file from a single piece without needing all pieces.
    • Ability to treat all compressed files as a single block, also known as the solid format.
    • Uses the AES encryption algorithm, where encrypted files are only recoverable by dictionary or brute force attacks.
    • Audio compression can hit up to 90%
    • It can even store NTFS streams and security information in the archives, both of which are usually lost upon compression.
    • Password protection can optionally protect filenames, so that the files contained within the archive will not be displayed without the right password.
    • .rar can also be embedded into other filetyps, like .jpeg. Check out this video.

  • .zip
    • Each archived file is compressed separately, allowing the use of different algorithms for a higher compression ratio on different files. The drawback lies in the archive being significantly larger when a large number of small files are compressed together. Contrary to this is the .tar.gz format that comprises of a .tar archive compressed using .gz
    • Files can also be stored uncompressed.
    • The AES encryption method have only been included since May 2003. Prior to that, .zip used a simple password-based symmetric encryption system which is known to be dangerously weak.
    • The uncompressed size of a file, compressed size of a file and total size of the archive was limited at 4 GB. Extensions had to be added to get around the limitations.
    • Unicode compatibility was only added in September 2006.
    • As the Info-ZIP Windows tools supports NTFS file system permissions, it will make an attempt to translate from NTFS permissions to Unix permissions or vice-versa when extracting files which can result in potentially unintended combinations like .exe files being created on NTFS volumes with executable permission denied.

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