Common Zip File Formats
Zip files (.zip and.zipx) have been referred to as compressed folders, packages, containers, and archives. Zip files are the most common type of archive files that also compress data.
Zip files were originally created for use with computers running DOS and then Windows operating systems. Today Zip files are also commonly used on other operating systems, such as the Mac and Unix operating systems. As mentioned above, the files archived in a Zip file are usually, compressed.
This saves space and also makes it easier to send them as email attachments. Zip files are also convenient for grouping data files. Rather than transporting, copying, or sending a number of files; you can zip them and easily work with one Zip file. Zip files are not the only archive type of file that you may encounter.
WinZip can be used to extract the contents of many as well. You may not even notice that you have downloaded another type of archive or that you received one by email. This is because WinZip associates itself with all of the archive file types with which it works and visually represents this association by causing the WinZip icon to display with the file name. In order to avoid confusion regarding your saved files, you may want to configure Windows to. Zip files (and other archives) contain information in a highly encoded form. In this form the information is not directly usable by other applications.
Jul 3, 2017 - ZIP is one of the most popular file compression formats. It was created in 1989 as the native format of the PKZIP program, which was introduced by Phil Katz in the wake of a lawsuit (which he lost) against him by the makers of the then-popular ARC program (and file format) for copyright and trademark.
With WinZip, you can extract the compressed files which will give you exact copies of the original ones in their original format. After extracting the contents of a Zip file, you have the option to delete the Zip file. Doing so will in no way affect the files that you extracted. However, you may also decide to keep the Zip file in an alternate location, such as an external drive, as a backup. With WinZip you can also create your own Zip files. Zip files are great when used to back up sets of your files (for example, folders with documents, photos, or source code).
Zip File Format Free
Keep in mind that creating a Zip file does not delete or change the original files. If you have any questions about this information please email.
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6.3.4 (1 October 2014; 3 years ago ( 2014-10-01)) Type of format Extended to (, ) (Microsoft) (ODF) (Mozilla extensions) from PKWARE? Yes ZIP is an that supports. A.ZIP file may contain one or more files or directories that may have been compressed.
The.ZIP file format permits a number of compression, though is the most common. This format was originally created in 1989 by, and was first implemented in 's utility, as a replacement for the previous compression format by Thom Henderson. The.ZIP format is now supported by many software utilities other than PKZIP. Microsoft has included built-in.ZIP support (under the name 'compressed folders') in versions of since 1998.
Apple has included built-in.ZIP support in 10.3 (via BOMArchiveHelper, now ) and later. Most have built in support for.ZIP in similar manners to Windows and Mac OS X.ZIP files generally use the '.zip' or '.ZIP' and the media type application/zip. ZIP is used as a base file format by many programs, usually under a different name. When navigating a file system via a user interface, graphical representing.ZIP files often appear as a document or other object prominently featuring a. Contents. History The.ZIP file format was created by of and Gary Conway of IDC (Infinity Design Concepts, Inc).
They created the format after PKWARE had a filed against them by Systems Enhancement Associates (SEA) claiming that his archiving products were derivatives of SEA's archiving system. SEA also threatened to sue Gary Conway and IDC for the same reasons, but then they found that SEA's work was actually a derivative of IDC's work and several others and opted not to proceed with the lawsuit. The name 'zip' (meaning 'move at high speed') was suggested by Katz's friend, Robert Mahoney.
They wanted to imply that their product would be faster than and other compression formats of the time. The earliest known version of.ZIP File Format Specification was first published as part of 0.9 package under the file APPNOTE.TXT in 1989. The.ZIP file format was released into the in 1989.
Version history The.ZIP File Format Specification has its own version number, which does not necessarily correspond to the version numbers for the PKZIP tool, especially with PKZIP 6 or later. At various times, PKWARE has added preliminary features that allow PKZIP products to extract archives using advanced features, but PKZIP products that create such archives are not made available until the next major release. Other companies or organizations support the PKWARE specifications at their own pace. The.ZIP file format specification is formally named 'APPNOTE -.ZIP File Format Specification' and it is published on the PKWARE.com website since the late 1990s. Several versions of the specification were not published. Specifications of some features such as compression, strong encryption specification and others were published by PKWARE a few years after their creation. The URL of the online specification was changed several times on the PKWARE website.
A summary of key advances in various versions of the PKWARE specification:. 2.0: (1993) File entries can be compressed with and use traditional PKWARE encryption. 2.1: (1996) Deflate64 compression.
4.5: (2001) Documented 64-bit zip format. 4.6: (2001) BZIP2 compression (not published online until the publication of APPNOTE 5.2). 5.0: (2002), supported for encryption (not published online until the publication of APPNOTE 5.2). 5.2: (2003) AES encryption support (defined in APPNOTE 5.1 that was not published online), corrected version of RC2-64 supported for encryption. 6.1: (2004) Documented certificate storage. 6.2.0: (2004) Documented Central Directory Encryption.
6.3.0: (2006) Documented Unicode filename storage. Expanded list of supported hash, compression (, ), encryption algorithms.
6.3.1: (2007) Corrected standard hash values for SHA-256/384/512. 6.3.2: (2007) Documented compression method 97. 6.3.3: (2012) Document formatting changes to facilitate referencing the PKWARE Application Note from other standards using methods such as the JTC 1 Referencing Explanatory Report (RER) as directed by JTC 1/SC 34 N 1621. 6.3.4: (2014) Updates the PKWARE, Inc.
Office address., starting with version 12.1, uses the extension.zipx for.ZIP files that use compression methods newer than DEFLATE; specifically, methods BZip, LZMA, PPMd, Jpeg and Wavpack. The last 2 are applied to appropriate file types when 'Best method' compression is selected. Standardization In April 2010, initiated a ballot to determine whether a project should be initiated to create an ISO/IEC International Standard format compatible with.ZIP. The proposed project, entitled Document Packaging, envisaged a.ZIP-compatible 'minimal compressed archive format' suitable for use with a number of existing standards including, and. In 2015, ISO/IEC 21320-1 'Document Container File — Part 1: Core' was published which states that that 'Document container files are conforming Zip files'. ISO/IEC 21320-1:2015 requires the following main restrictions of the ZIP file format:.
Files in ZIP archives may only be stored uncompressed, or using the 'deflate' compression (i.e. Compression method may contain the value '0' - stored or '8' - deflated). The encryption features are prohibited.
The digital signature features are prohibited. The 'patched data' features are prohibited. Archives may not span multiple volumes or be segmented. Design.ZIP files are archives that store multiple files.ZIP allows contained files to be compressed using many different methods, as well as simply storing a file without compressing it. Each file is stored separately, allowing different files in the same archive to be compressed using different methods. Because the files in a.ZIP archive are compressed individually it is possible to extract them, or add new ones, without applying compression or decompression to the entire archive.
This contrasts with the format of compressed files, for which such random-access processing is not easily possible. A directory is placed at the end of a.ZIP file.
This identifies what files are in the.ZIP and identifies where in the.ZIP that file is located. This allows.ZIP readers to load the list of files without reading the entire.ZIP archive.ZIP archives can also include extra data that is not related to the.ZIP archive. This allows for a.ZIP archive to be made into a self-extracting archive (application that decompresses its contained data), by prepending the program code to a.ZIP archive and marking the file as executable. Storing the catalog at the end also makes possible hiding a zipped file by appending it to an innocuous file, such as a GIF image file. The.ZIP format uses a 32-bit CRC algorithm and includes two copies of the directory structure of the archive to provide greater protection against data loss. Structure. ZIP-64 Internal Layout A.ZIP file is correctly identified by the presence of an end of central directory record which is located at the end of the archive structure in order to allow the easy appending of new files.
If the end of central directory record indicates a non-empty archive, the name of each file or directory within the archive should be specified in a central directory entry, along with other metadata about the entry, and an offset into the.ZIP file, pointing to the actual entry data. This allows a file listing of the archive to be performed relatively quickly, as the entire archive does not have to be read to see the list of files. The entries within the.ZIP file also include this information, for redundancy, in a local file header. Because zip files may be appended to, only files specified in the central directory at the end of the file are valid. Scanning a ZIP file for local file headers is invalid (except in the case of corrupted archives), as the central directory may declare that some files have been deleted and other files have been updated.
For example, we may start with a.ZIP file that contains files A, B and C. File B is then deleted and C updated. This may be achieved by just appending a new file C to the end of the original ZIP file and adding a new central directory that only lists file A and the new file C. When ZIP was first designed, transferring files by floppy disk was common, yet writing to disks was very time consuming. If you had a large zip file, possibly spanning multiple disks, and only needed to update a few files, rather than reading and re-writing all the files, it would be substantially faster to just read the old central directory, append the new files then append an updated central directory. The order of the file entries in the central directory need not coincide with the order of file entries in the archive.
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Each entry stored in a ZIP archive is introduced by a local file header with information about the file such as the comment, file size and file name, followed by optional 'extra' data fields, and then the possibly compressed, possibly encrypted file data. The 'Extra' data fields are the key to the extensibility of the.ZIP format.
'Extra' fields are exploited to support the ZIP64 format, WinZip-compatible AES encryption, file attributes, and higher-resolution NTFS or Unix file timestamps. Other extensions are possible via the 'Extra' field.ZIP tools are required by the specification to ignore Extra fields they do not recognize. The.ZIP format uses specific 4-byte 'signatures' to denote the various structures in the file. Each file entry is marked by a specific signature. The end of central directory record is indicated with its specific signature, and each entry in the central directory starts with the 4-byte central file header signature. There is no BOF or EOF marker in the.ZIP specification.
Conventionally the first thing in a.ZIP file is a.ZIP entry, which can be identified easily by its local file header signature. However, this is not necessarily the case, as this not required by the.ZIP specification - most notably, a self-extracting archive will begin with an executable file header. Tools that correctly read.ZIP archives must scan for the end of central directory record signature, and then, as appropriate, the other, indicated, central directory records. They must not scan for entries from the top of the ZIP file, because only the central directory specifies where a file chunk starts. Scanning could lead to false positives, as the format does not forbid other data to be between chunks, nor file data streams from containing such signatures. However, tools that attempt to recover data from damaged.ZIP archives will most likely scan the archive for local file header signatures; this is made more difficult by the fact that the compressed size of a file chunk may be stored after the file chunk, making sequential processing difficult. Most of the signatures end with the short integer 0x4b50, which is stored in little-endian ordering.
Viewed as an ASCII string this reads 'PK', the initials of the inventor Phil Katz. Thus, when a.ZIP file is viewed in a text editor the first two bytes of the file are usually 'PK'. (DOS, OS/2 and Windows self-extracting ZIPs have an before the ZIP so start with 'MZ'; self-extracting ZIPs for other operating systems may similarly be preceded by executable code for extracting the archive's content on that platform.) The.ZIP specification also supports spreading archives across multiple filesystem files. Originally intended for storage of large.ZIP files across multiple, this feature is now used for sending.ZIP archives in parts over email, or over other transports or removable media.
The of DOS has a timestamp resolution of only two seconds;.ZIP file records mimic this. As a result, the built-in timestamp resolution of files in a.ZIP archive is only two seconds, though extra fields can be used to store more precise timestamps. The.ZIP format has no notion of, so timestamps are only meaningful if it is known what time zone they were created in. In September 2007, PKWARE released a revision of the.ZIP specification providing for the storage of file names using, finally adding Unicode compatibility to.ZIP. File headers All multi-byte values in the header are stored in byte order. All length fields count the length in bytes. Local file header Offset Bytes Description 0 4 Local file header signature = 0x04034b50 (read as a little-endian number) 4 2 Version needed to extract (minimum) 6 2 General purpose bit flag 8 2 Compression method 10 2 File last modification time 12 2 File last modification date 14 4 CRC-32 18 4 Compressed size 22 4 Uncompressed size 26 2 File name length ( n) 28 2 Extra field length ( m) 30 n File name 30+ n m Extra field The extra field contains a variety of optional data such as OS-specific attributes.
It is divided into chunks, each with a 16-bit ID code and a 16-bit length. This is immediately followed by the compressed data. If the bit at offset 3 (0x08) of the general-purpose flags field is set, then the CRC-32 and file sizes are not known when the header is written. ^, 20 July 1993, retrieved 5 January 2012.
The New York Times. Retrieved 14 June 2009.