What is the Z01 file format?
.z01 is the first of multiple files that together form a split archive, widely associated with WinZip. The file stores compressed data that, when combined with all remaining volume files, reconstructs a complete ZIP archive. The split-ZIP convention is defined by PKWARE in the ZIP specification (APPNOTE) and is supported across all major archiving tools.
When are split archives used?
.z01 files use the same compression and archiving standard as regular .zip files. Splitting a large archive into smaller volumes makes sharing files over the internet easier and allows overcoming size limitations imposed by email services, cloud storage providers, or older file systems. Splitting is typically used for very large file archives.
Unpacking and archive structure
The .z01 extension marks the first volume of the split archive. Each subsequent volume is assigned a sequentially numbered extension - .z02, .z03, and so on - while the final segment carries the plain .zip extension. A .z01 file is not self-contained: the central directory and end-of-archive record reside only in the final .zip segment, so .z01 cannot be opened on its own. Unpacking can be completed only when all split volume files are present in the same folder; the tool will then automatically reassemble the original archive from its parts.
Security & safety
RISK: MEDIUMA split ZIP carries the same risks as any ZIP - it can contain malware, and you only see that after extracting, so scan unexpected archives before running anything inside. The .z01-specific gotcha is not security but completeness: if any part is missing (especially the final .zip that holds the index, or a middle volume the data passes through), the archive simply won't extract and the missing bytes cannot be recovered. Verify you have a continuous set (.z01, .z02 … plus the .zip) before relying on it.
Format details
in a nutshellPrograms that open Z01 files
Windows4 apps
WinZip
Paid Open the final .zip part (not the .z01) with every segment in the folder. WinZip created this split scheme. 
WinRAR
Paid Gather all parts in one folder, then open/extract the last .zip; WinRAR joins the .z01/.z02… volumes automatically. 
7-Zip
Open-source Put all parts in one folder. Right-click the FINAL .zip > 7-Zip > Extract Here. (Opening the .z01 directly won't work.) Free. 
PeaZip
Open-source Open the final .zip with all parts present in the same folder; PeaZip reassembles and extracts. Free. (URL moved to peazip.github.io.) 
macOS2 apps
The Unarchiver
Free Place all parts together and open the final .zip; The Unarchiver handles split ZIP volumes. macOS Archive Utility often cannot. 
Linux2 apps
Xarchiver
Open-source Open the final .zip with all volumes present in the same directory. (Active fork on GitHub.) 
7-Zip / p7zip
Open-source Gather the parts and run: 7z x archive.zip (the final part). It reads the .z01/.z02 siblings automatically. Technical details
deep spec| Format type | First volume of a multi-part split ZIP archive (binary) |
| MIME type | application/zip |
| Magic bytes | 50 4B 03 04 ("PK\x03\x04") at offset 0 - standard ZIP local file header; some spanned ZIPs instead begin with a 4-byte PK\x07\x08 spanning signature |
| Standalone opening | Not possible - the central directory and end-of-archive record are stored only in the final .zip segment, making .z01 unreadable in isolation |
| Volume naming scheme | First segment: .z01; subsequent segments: .z02, .z03, … (sequentially numbered); final segment: .zip |
| Defined by | PKWARE ZIP Application Note (APPNOTE.TXT) - split and spanned archive section |
| Compression methods | Supports all standard ZIP compression methods: Stored, Deflate, Deflate64, BZIP2, LZMA, and others |
| Encryption support | ZipCrypto (legacy) and AES-128 / AES-256 (WinZip AE-x) per entry, identical to standard ZIP |
| Max volume size - legacy ZIP | Up to 4 GB per segment using 32-bit ZIP fields |
| ZIP64 support | Supported - ZIP64 extension removes the 4 GB per-segment and 4 GB total-archive limits |
| Required for extraction | All numbered volumes (.z01, .z02, …) plus the final .zip segment must be present in the same directory |
| File data placement | Compressed file data begins in .z01 and may span across multiple volumes; no volume is individually decodable |
| Platform support | Windows, macOS, Linux - via WinZip, 7-Zip, WinRAR, PeaZip, The Unarchiver, Keka, p7zip |
| Related formats | .z02 / .z03 (subsequent volumes), .zip (final segment and standard archive), .zipx (WinZip extended ZIP) |
| Released | Split/spanned ZIP defined in PKWARE APPNOTE; .z01 naming used by WinZip and others |
| Open standard | Yes · royalty-free |
| Specification | pkware.cachefly.net |
Z01 conversions
Community Q&A
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