ZIP (ZIP Archive)
The format that turned file compression into a household word, invented in 1989 and still the default way the world bundles files.
| Full name | ZIP Archive |
| Extension | .zip |
| MIME type | application/zip |
| Developer | Phil Katz (PKWARE) and Gary Conway (Infinity Design Concepts) |
| Released | 1989 |
| Type | Archive / lossless compression |
| Default compression | Deflate (method 8) |
| Spec document | APPNOTE.TXT (maintained by PKWARE) |
What is a ZIP file?
ZIP is an archive format created by Phil Katz of PKWARE and Gary Conway of Infinity Design Concepts, released on February 14, 1989. Katz published the format specification in a public document called APPNOTE.TXT, making the format open for anyone to implement. It quickly became the standard way to bundle and compress files on personal computers.
A .zip file is a container that holds one or more files and folders in a single binary package. Each entry inside the archive is compressed and stored independently, meaning you can extract a single file without decompressing the entire archive. The format stores file names, sizes, checksums, and compression metadata alongside the data itself. It supports optional password-based encryption, though the original encryption scheme is weak by modern standards.
History
Phil Katz created ZIP in 1989 after Systems Enhancement Associates sued his company PKWARE over PKARC, which was based on an older archive format called ARC. Rather than fight the lawsuit, Katz designed a new format from scratch and placed the specification in the public domain. His tool PKZIP made the format popular on DOS machines throughout the early 1990s, and ZIP later became a native archive format in Windows XP, macOS, and most Linux desktop environments.
How it works
A ZIP file is built from three sections: a series of local file entries, an optional archive decryption header, and a central directory at the end of the file. Each local file entry has a header with the file name, compression method, CRC-32 checksum, and compressed size, followed by the compressed data. The central directory at the end lists all entries with their offsets into the file, so tools can read the archive without scanning it from the beginning. The format ends with an end-of-central-directory record that gives the size and location of the central directory.
What it is used for
- Distributing software, plugins, and theme packages as a single downloadable file
- Sending multiple documents or images as one email attachment
- Bundling website assets, fonts, or icon sets for download
- Archiving project files or backups in a format any operating system can open
How to open it
Windows, macOS, and most Linux desktop environments open .zip files without installing any additional software. For more control over extraction, tools like 7-Zip (Windows/Linux) and The Unarchiver (macOS) add batch extraction, password support, and preview without extracting.
Pros and cons
Strengths
- Built-in support on every major operating system with no extra software needed
- Per-file compression lets you extract one file without unpacking the whole archive
- Open specification with no licensing fees, widely implemented across tools and languages
- Supports files and archives of practically any size (ZIP64 extension lifts the 4 GB per-file limit)
Trade-offs
- Deflate compression is weaker than newer algorithms like LZMA2 (used in 7Z) or Brotli
- Original ZipCrypto encryption is insecure and should not be used for sensitive data
- No solid compression mode, so archives of many small similar files are larger than 7Z equivalents
- Central directory at the end makes streaming creation awkward without writing a placeholder
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ZIP FAQ
Is ZIP compression lossless?
Yes. ZIP uses the Deflate algorithm, which is fully lossless. Every byte of every file you put in comes out exactly the same when you extract it.
How secure is ZIP password protection?
The original ZipCrypto scheme built into most ZIP tools is weak and can be cracked quickly with known-plaintext attacks. If you need real encryption, use AES-256 (supported in modern ZIP tools like 7-Zip) or encrypt with a separate tool before zipping.
What is the maximum file size in a ZIP archive?
The original ZIP format caps individual files and archives at 4 GB. The ZIP64 extension, supported by all modern tools and operating systems, removes that limit and allows files and archives up to 16 exabytes.
Why does my ZIP file not compress well?
Deflate works best on plain text, code, and uncompressed data. Files that are already compressed (JPEG images, MP4 videos, MP3 audio, PDF documents with embedded images) contain little redundancy, so Deflate adds almost nothing and the ZIP ends up nearly the same size as the originals.