ZIP (archive)
/zɪp/ · noun · archive format
ZIP is an archive format that packs many files and folders into one compressed file. Every major operating system can open it.
In more detail
A ZIP file bundles files and folders into a single file and usually compresses each one with the lossless DEFLATE method. Extracting it gives back the exact originals.
Phil Katz introduced the format with PKZIP in 1989. Windows, macOS, iOS, Android and ChromeOS all open and create ZIP files with built-in tools, which makes it the default way to send a group of files.
How a ZIP file is organized
Each file is stored as its own compressed entry, with a header giving its name, size and compression method. A central directory at the end of the archive lists every entry and where it starts. Tools read that directory first, which is why they can show the contents and pull out one file without unpacking the rest.
Compressing files separately keeps extraction fast and limits damage, but it can't share patterns between files. Formats such as 7z and RAR in solid mode often make smaller archives for many similar files.
Limits and encryption
The original format caps files and archives at 4 GB. The ZIP64 extension removes that limit, and most current tools write it when needed. Classic ZIP password protection is weak, and the stronger AES extension isn't opened by every built-in tool.
Folders that contain __MACOSX entries or ._ files were zipped on a Mac. Those hold Finder metadata and can be ignored.
Key points
- ZIP compresses each file separately with lossless compression.
- Every major operating system opens ZIP files without extra software.
- For the smallest archives of similar files, 7z or RAR often do better.