General Information About ZIP Files
ZIP files are compressed archives that group together one or more files into a single file, compressing the files (making them smaller) that are contained inside. The ZIP file format is very popular for efficiently storing and transferring groups of files in a variety of business and personal applications.
The ZIP file format dates to the late 1980s when it received heavy use in pre-internet-era Bulletin Board Systems, or BBSes. In this era, file transfers occurred using MODEMs and transfer speeds were very limited. Using ZIP compression regularly saved minutes or even hours off of file transfers. It also allowed for multiple files and folders to be grouped together ("zipped") and transferred as a single ZIP file. Once received, the ZIP file would then be opened and its contents decompressed ("unzipped") onto a user's computer.
Today, the ZIP file format remains in heavy use in the internet and in the cloud, with billions of such files in circulation. In the cloud, ZIP files are commonly found as both Gmail attachments, as well as files stored in Google Drive or other cloud-based storage systems such as Dropbox and Microsoft OneDrive.
In addition to compression, ZIP files are archives that can group together multiple files and folders. When this is done, the path and folder information of the file tree is preserved inside the ZIP file. This makes the ZIP file format convenient for sharing and distributing groups of files.
Examples of ZIP File Uses
ZIP files are common across a variety of business areas, including industries ranging from medical, insurance, legal, mortgage, banking and financial, scientific, equities and trading, SEO (Search Engine Optimization), and education industries.
Here are some specified real-world examples of actual usage of ZIP files:
- A car insurance agent ZIPs and emails information related to a person's health insurance, homeowner's insurance, auto insurance, or life insurance policy.
- A real estate agent scans and ZIPs a sales contract and sends it to a mortgage broker for a home loan when buying a home.
- An attorney or lawyer for a law firm ZIPs together a set of related legal documents such as a will, trust, claim, or other estate planning documents and shares them with their client.
- A university student ZIPs a homework assignment and related files and sends it to their instructor or professor in an online degree program.
- A tax accountant ZIPs and emails a copy of a person's federal and state tax returns for review before filing with the IRS.
ZIP files can contain multiple files of different types. Common files that can be included in a ZIP archive include PDFs, images, videos, and Microsoft Office documents including Microsoft Word, Microsoft Excel, and Microsoft PowerPoint (*.DOCX, *.XLSX, *.PPTX file formats).
Creating and Opening ZIP Files
ZIP Extractor and most modern operating systems have built-in functionality to create ZIP files.
- On Windows or PC, to create a ZIP file, right-click files in Windows Explorer and select “Send to -> Compressed (zipped) Folder.”
- On a Mac running Mac OS, create a ZIP file by right-clicking files in Finder and select "Compress [name_of_file].”
- On a Chromebook running Chrome OS, choose one more files in the Files app and then select “Zip selection.”
- In ZIP Extractor, click "Create New ZIP" and from there you can add files and folders to be compressed, including files from Google Drive. You can also drag-and-drop files and folders onto the main screen to ZIP them.
- In your internet browser, you can also use the URL shortcut zip.new to go directly to the ZIP Extractor "Create New ZIP" screen.
On Windows, Mac, or Chrome OS, a ZIP file can be extracted (decompressed) by double-clicking it. Then, the individual files will be unzipped into a new directory and available to preview, edit, print, etc.
ZIP Extractor provides the same decompression functionality that standard operating systems provide, except that ZIP Extractor supports many more formats than the basic built-in functionality of most ZIP programs. Most importantly, ZIP Extractor is designed bottom-up to work directly in the cloud. Because there is no built-in ability to unzip ZIP files in Google Drive or Gmail, ZIP Extractor is a third-party application that provides this functionality.
Encryption and Password Protection
The ZIP file format provides support for basic password-protected ZIP files. More recently, the ZIP format was enhanced with the ability to create files with strong encryption, using AES (Advanced Encryption Standard). This "strong encryption" approach is much more secure than the original version, but it is less compatible because Windows and Mac cannot open them. ZIP files using "strong encryption" require ZIP Extractor, WinZip, or other more advanced program to open.
Other archive formats, including RAR and 7-Zip, also allow passwords. These formats have a special ability to also encrypt the names of the files contained in the archive file (using the supplied password), in addition to file content.
ZIP Extractor has full support for opening ZIP, RAR, and 7-Zip files with all types of passwords and encryption formats. It can also create ZIP files with both the standard encryption (compatible with Windows and Mac) or "strong encryption" (requiring ZIP Extractor or WinZip to open).
Compressed Archive File Formats: ZIP, RAR, and 7-Zip
The three most common file compression formats in circulation today are ZIP, RAR, and 7-Zip; ZIP files are the most common. Details for each file type are provided below.
The ZIP File Format
The ZIP file format is notable for being both an archive file format (which can contain multiple files and folders) as well as a compression file format (which means the file data itself can be compressed). Although ZIP files are by far the most common such compressed archive format, there are others, described below.
The ZIP file format was introduced by PKWARE® in 1989, and the file format and specification have been evolving ever since. The formal ZIP file specification is published as an Application Note by its creator PKWARE.
The ZIP file format is notable for supporting many different compression methods. The traditional compression method used by ZIP files, referred to as Deflate, is by far the most common. When a ZIP file is created with ZIP Extractor or your operating system, these are generally the compression methods used. However, certain ZIP programs can create ZIP files using more advanced compression methods including LZMA, BZIP2, PPMD, and XZ (LZMA2).
ZIP Extractor supports opening all types and versions of ZIP files. Full support is provided for ZIP files using any of the above compression methods, including encrypted ZIP files requiring a password to open.
RAR File Format
The RAR file format (from Roshal ARchive named after its author Eugene Roshal) is conceptually similar to ZIP files in that it supports archiving (grouping) files and folders together into a single file, while also compressing the file data. The RAR format dates back to the early 1980s, and can provide high compression ratios (producing smaller files). However, this comes at the expense of speed, with the PPMd and LZMA compression methods used by RAR having generally higher computational demands than the Deflate algorithm used by ZIP.
RAR is a highly proprietary format, and RAR files may only be created using the WinRar software program or companion command-line tool. Fortunately, the ability to open and decompress RAR files is "open source" and there are many programs that can do this, including ZIP Extractor.
ZIP Extractor has full support for opening the latest version of the RAR file format (Version 5) as well as older versions (Version 3 and Version 4). This includes full support for RAR files with a password. More information can be found at the Library of Congress entry for RAR files.
7-Zip (7z) File Format
The 7-Zip file format (also known as 7z) is a relatively new compressed archive format that, like ZIP and RAR, supports grouping and compressing multiple files and folders into a single file. This format generally uses the LZMA and LZMA2 compression method by default. However, the open architecture of the 7-Zip format provides support for other compression methods including BZIP2, PPMd, and ZIP's Deflate. In practice, however, 7-Zip files created with these compression methods are rare.
Notably, the 7-Zip format provides support for filters, which can lead to greater compression ratios on certain types of files. For example, the BCJ filter used by 7-Zip can result in smaller file sizes for certain executable file formats (such as *.exe files).
ZIP extractor supports opening all variants of 7-Zip files, using any combination of compression method and filter. This also includes full support encrypted and password-protected 7-Zip files.
The TAR Archive File Format
The TAR file format (from Tape ARchive) is a long-established format that is very important to computing in general. Being an archive format, TAR files do not involve compression at all. Instead, the purpose of a TAR file is to group together (or archive) sets of files and folders in a reliable way.
TAR is a well established, long-running file archiver program that has received important updates over the years. It is generally considered well suited to the task of "archiving" and is appropriate for long-term storage and preservation of sets of files. Originally, this was designed for archival storage on tape drives circa early 1980s (hence its name, Tape ARchive). More commonly today it is encountered on UNIX/Linux systems to create compressed files when used in conjunction with a compressor.
Importantly, the TAR file format by itself doesn't handle compression. For this reason TAR files are almost always subsequently compressed with a pure compression method that isn't responsible for archiving. Such methods, described below, by design do not record any archive information about the data being compressed, such as file names or sizes. In this sense, the TAR file's job is to archive (group) files and folders, while a compressor's job is to compress the resulting TAR file into a smaller file.
Most commonly, after the TAR file is created, compression is then done using the GZIP compression program (described below). This results in a file with extension *.tar.gz, where the gz indicates compression of the TAR file with the GZIP program. The BZIP2, LZIP, and XZ compression programs can also be used, resulting in files with extension *.tar.bz2, *.tar.lz, and *.tar.xz, respectively.
GZIP, BZIP2, XZ, and LZIP File Compressors
Separate from the archiving task performed by TAR is the task of data compression. This is done by compression methods that operate purely on a generic stream of data, and which do not record any archive information about the files contained within. The most common examples include:
- The GZIP file format (*.tar.gz or *.tgz). Applies Deflate compression to the file data, with some additional metadata. In common use but has some problems with the format specification. More information available at gzip.org.
- The BZIP2 file format (*.tar.bz2 or *.tbz). Applies BZIP2 compression to the file data, and includes metadata including built-in data integrity checks for each compressed block. More information available at sourceware.org/bzip2.
- The LZIP file format (*.tar.lz or *.tlz). Applies LZMA compression to the file, with important features such as data integrity and indexing to allow for efficient multi-block processing and parallel decompression. More information available at nongnu.org/lzip.
- The XZ file format (*.tar.xz or *.txz). Applies LZMA2 compression to the file data with special features to support parallel / multi-threaded decompression. More information available at tukaani.org/xz.
ZIP Extractor supports opening and decompressing all of the above compressed TAR formats.
Data compression has a long and interesting history. Over the years, this field has produced a wide variety of compressed file formats. These formats range from those commonly used today (as explored above) to more obscure ones that never gained traction. For further reading, see the List of archive formats.