ZIP64

ZIP64 is an extension of the ZIP file format that enables archives and files far larger than the original limits of 4 gigabytes per file and 65,535 total entries per archive. It was designed to accommodate large data sets, software distributions, backups, and other use cases that require substantial storage capacity.

At the core of ZIP64 are two additional records: the ZIP64 End of Central Directory Record and the ZIP64 End of Central Directory Locator. The ZIP64 EOCD record provides 64-bit versions of the central directory size, the archive size, and the total number of central directory entries, while the locator points to the EOCD64. In the traditional ZIP structures, many fields are 32-bit and can be replaced by ZIP64 extended sizes; when this happens, the corresponding 32-bit fields are typically set to 0xFFFFFFFF to indicate ZIP64 values are used. With ZIP64, a single file can be up to 2^64−1 bytes, the central directory can refer to up to 2^32−1 entries, and the archive can be up to 2^64−1 bytes in size.

Compatibility and support vary. Most modern compression tools and libraries (such as 7-Zip, WinZip, WinRAR, The Unarchiver, and popular programming libraries) recognize and create ZIP64 archives. Older tools or some embedded systems may not read ZIP64 data reliably and may fail to extract or create such archives.

Adoption and usage: ZIP64 is widely used for large backups, disk images, and distribution packages that exceed the original ZIP limits. It is part of the ZIP specification maintained by PKWARE, and support has become standard in contemporary software, contributing to interoperability across platforms.