TL; DR: After its launch in 1999, 7-Zip quickly gained momentum as a popular archiving application among commercial organizations and independent users. With a number of unique features, the 7z format is famous for its much higher compression ratio than traditional archivers. And, since its inception, 7-Zip’s free, open-source file compression software has attracted millions of users due to its ease of use and compatibility with an array of compression, conversion, and encryption methods.//
It was a common scene in the early 2000s. Two professionals are working in unison on a single project in offices separated by miles of geography. In one office, Jeremy bangs away at the keyboard, stopping here and there to contemplate the Amy Winehouse poster he just hung on the wall. Across state lines at the company’s satellite office, Steve checks his inbox for Jeremy’s message after catching the end of a rerun of Friends in the break room.
Jeremy and Steve are collaborating on a presentation for their company’s upcoming B2B meeting. Before the social media explosion, before the iPhone, and before DropBox, the duo primarily relies on email for communication and file sharing. After creating the layout and some of the slides for the presentation, Jerry sends the PowerPoint file to Steve for his next contribution.
Anticipating a rather in-depth meeting, Steve adds many relevant charts, pictures, and graphs to the document. With more than 50 media-heavy slides — and nothing but early DSL — Steve decides to send the files in a ZIP archive, hoping for a quick and painless transfer. However, the archive is still over 12MB, much too large for an email attachment. He then remembers other archive formats and takes to the internet to research them.
Reading about a number of uncommon formats, Steve’s anxiety grows until he comes across two promising alternatives — RAR and 7z. After some contemplation, he decides that using RAR would be too tedious, as it may require the file to be split into multiple numbered archives. Finally deciding on 7-Zip, Steve is able to compress the file down to 7MB without any splitting. In addition, he is able to make the file self-extracting, meaning Jeremy will be able to view the archive as soon as he receives it. With their deadline fast approaching, the duo finds newfound confidence in their ability to share and collaborate on important company projects.
A Unique Archiver Enjoying Widespread Use Since 1999
While 7-Zip is far from the earliest archiver, it is notable as a major pioneer in compression technology alongside WinRAR and WinZIP. The first iteration of the ZIP format was created in 1989 by Phil Katz for his PKZIP utility.
Using DEFLATE for its main compression algorithm, ZIP/PKZIP was one of the first archivers in widespread use, with Windows including baked-in ZIP compatibility several years later. Meanwhile, Eugene Roshal had released WinRAR, an improved albeit less popular format which featured higher compression, better encryption, and the use of a recovery record.
After the dust began to settle between RAR and ZIP, 7-Zip was released in late 1999 by Igor Pavlov, an aspiring and enthusiastic freelance developer from Russia. Boasting many of the same features as WinRAR, 7-Zip soon became a popular third option.
Featuring a built-in file manager, as well as an open-source SDK and several command line variants, 7-Zip was highly favored by both developers and end users. Additionally, 7-Zip introduced AES-256 encryption in its early releases, beating RAR to the punch by several years.
Astounding Compression Ratios Courtesy of the 7z Format
The 7z format is touted as having the highest compression ratio of any archive file format. It was one of the first archivers to consistently feature preprocessing filters to achieve higher compression rates. Although all WinRAR versions support filters similar to those used in 7z, the latest versions of WinRAR don’t support the exotic features of VM filters that were included in previous WinRAR releases.
Although RAR compression uses similar technology, the filters used by 7-Zip are more thorough, resulting in greater compression during the later processing stages. The company was the first archiver to use the LZMA algorithm, which uses an internal dictionary to encode data bit by bit.
The BCJ and BCJ2 preprocessors and delta filter for multimedia data power the LZMA compression method. The filters ease compression by making jump targets — or byte addresses — easier to find. Preprocessing converts the byte addresses for jumps and calls into absolute values in place of using relative position cues, which results in identical encoding. Since the encoding is now more congruent, these jumps become more predictable and compressible.
In a 2014 experiment run by HowToGeek, several popular games, including Bastion and Hotline Miami, were compressed in ZIP, RAR, and 7z formats to benchmark 7-Zip’s true compression ability. Hotline Miami, with its 654MB of data, was reduced to an impressive 301MB by 7-Zip, clocking in at just 46% of the original file size. Meanwhile, WinZip and WinRAR resulted in 48% and 46.9% respectively.
Although the difference may seem subtle, fewer megabytes in each archive yields significant storage savings with repeated use. Further, 7-Zip is capable of much higher compression rates than those specified in its default settings. While highly compressed archives may take longer to process and decompress, the choice is clear for anyone looking to save as much space as possible — or make their file uploads and downloads run smoother.
Encouraging Open-Source Development With the LZMA SDK
Aside from developing and maintaining an outstanding product, Igor has made the LZMA SDK readily available to developers. The LZMA SDK was under the GNU Lesser General Public License (GNU LGPL) until it was placed in the public domain in 2008. This freed the code to be used in projects without any condition. However, 7-Zip’s main code is still under the GNU LGPL.
A long-established tenet of the open-source community is its continuous improvement of existing code and applications powered by a combination of software engineers, freelance developers, and even casual tech enthusiasts.
The LZMA SDK currently includes the C++ source code for the LZMA Encoder and Decoder and a reduced version of 7z’s compression and decompression codes. The kit also includes ANSI-C, C#, and Java compatible variants, as well as SFX modules to create self-extracting archives.
Major features include compression speeds averaging 3MB/s, decompression speeds ranging from 5 to 50MB/s, and very small memory requirements. Using the SDK, developers have created a number of tools for Unix-based systems such as XZ and LZip. In addition, DotNetCompression, a popular compression library by Noemax, implements LZMA into its maximum-compression streaming technology, making large video streams much easier to broadcast and view.
A Continued Focus on Security and Accessibility
Given its high compression ratio and fast decompression capabilities, the 7z format is suitable for a variety of use cases that range from simple space conservation to encrypting large collections of documents. Embedded applications, such as firmware stored in ROMS, are limited by memory and code space constraints, making compression essential for fast operation. On the other hand, JPEG images — which have significantly grown in size over the years — can more easily be stored, shared, and loaded when compressed. For example, an image-heavy website may suffer from poor performance as it attempts to load massive amounts of uncompressed files.
Because 7-Zip and the LZMA SDK are open-source, the project and its offshoots are ever-evolving. While Igor maintains the official 7-Zip releases, the community continually strives for the improvement of related LZMA software. With nearly two decades under its belt, the 7-Zip archiver has undergone a number of changes ranging from bug fixes to added features. In September 2002, Encryption for the ZIP format was included, followed by AES-256 encryption for the 7z format four months later. The drag-and-drop feature was added shortly after, along with toolbars and other GUI enhancements. The current incarnation of 7-Zip supports multi-core CPU threading, dynamically sized volumes, and the opening of executables as archives without the need to run them.
Over the years, 7-Zip has been localized in over 87 languages, making high-compression archiving accessible to a growing number of people. With a sustained focus on security and user-friendliness, 7-Zip remains one of the most popular archivers, with millions of users in homes and offices worldwide. With compression, the files we use every day are able to be transformed into neat, compact, and easy-to-handle packages.