What is the 7Z.001 file format?
Files with the .7z.001 extension store the first part of a split archive created using the 7-Zip archiver. The full filename typically consists of the original archive name and the .7z.001 suffix, with subsequent parts carrying sequentially numbered suffixes - .7z.002, .7z.003, and so on. Such an archive can store any type of data, though the compression method may not be optimal for every data type.
Creating and extracting a split archive
Archive part files store information about which parts are needed to extract the archive. If any one of the parts is missing, extracting the archive is not possible. All part files must be placed in the same folder before extraction. Split archives can be created using 7-Zip or other file archiving tools that support this format. Split-archiving is commonly used for large files, when sending files as email attachments, or when only limited storage space is available on a single medium.
7-Zip file format
A .7z.001 file is the opening volume of a larger .7z split archive. Because 7-Zip performs a byte-level split of the finished .7z container, only the first volume carries the standard 6-byte 7z signature (37 7A BC AF 27 1C at offset 0). Later volumes - .7z.002, .7z.003, and so on - are raw byte ranges with no signature of their own. The end-header and file index reside in the last volume, so the .7z.001 file alone cannot be extracted even if it is fully intact.
The 7Z format was developed in 1999 by Igor Pavlov as an efficient, open-source data compression method. It supports the following compression algorithms:
- LZMA (default algorithm)
- LZMA2
- PPMd
- BCJ and BCJ2 (executable pre-processing filters)
- BZip2
- Deflate
The format also supports AES-256 encryption and additional compression options. Archive headers can also be compressed and encrypted. 7Z does not offer a data recovery feature, so recovering missing or corrupted data automatically with 7-Zip is not possible - unlike RAR split volumes, which can include a recovery record.
Security & safety
RISK: MEDIUMA split 7z set is only as safe as whatever was compressed inside - most often a download whose real file types you won't see until after joining and extracting, so scan unexpected .7z.001 sets before running anything in them. The .7z.001-specific gotcha is completeness, not security: every volume must be present with unbroken numbering (.001, .002, .003 …) and original names, or extraction fails and the missing bytes cannot be recovered. 7z volumes can also be AES-256 encrypted (sometimes used to evade antivirus), so be wary of password-protected sets sent unsolicited. Prefer 7-Zip / PeaZip / Keka from their official sites over "file joiner" download portals that bundle adware.
Format details
in a nutshellPrograms that open 7Z.001 files
Windows4 apps
7-Zip
Open-source Put all parts in one folder. Right-click 7z.001 > 7-Zip > Extract Here; it joins the .002/.003 volumes automatically. Free, the go-to tool. 
WinRAR
Paid With every part in the folder, open the .7z.001; WinRAR extracts the joined 7z. (7-Zip is the free choice.) 
PeaZip
Open-source Open the .7z.001 with all volumes present; PeaZip reassembles and extracts. Free GUI. 
NanaZip
Open-source Modern 7-Zip fork with Windows 11 right-click menus; right-click the .7z.001 > Extract. 
macOS2 apps
Keka
Free Drag the .7z.001 onto Keka with all volumes in one folder; it joins and extracts. The go-to free Mac archiver. 
Linux2 apps
7-Zip / p7zip
Open-source Run '7z x archive.7z.001' with all parts in the folder; it reads the .002/.003 volumes automatically. 
Android1 app
ZArchiver
Free Browse to the .7z.001 with all parts in one folder, tap and Extract; supports split 7z. Technical details
deep spec| File role | First volume of a 7z multi-volume split set; acts as the entry point for the entire split archive |
| MIME type | application/x-7z-compressed |
| Magic bytes | 37 7A BC AF 27 1C (6 bytes at offset 0) - the standard 7z signature, present only in the first volume (.7z.001) |
| Volume naming convention | Sequential zero-padded numeric suffix appended after .7z: .7z.001, .7z.002, .7z.003, … |
| Split method | Byte-level ("dumb") split of a completed .7z archive - no per-volume headers or footers are added to individual volumes |
| Archive index location | End-header and file index are stored exclusively in the last volume; the .7z.001 alone is not extractable |
| Extraction dependency | All volumes must be present in the same directory; a single missing part makes extraction impossible |
| Compression algorithms | LZMA (default), LZMA2, PPMd, BZip2, Deflate, BCJ and BCJ2 pre-processing filters |
| Encryption | AES-256; filename encryption can optionally hide the file list from unauthorized users |
| Header encryption | Archive headers, including the file index, can be independently compressed and encrypted |
| Data recovery | No built-in recovery record; corrupted or missing volumes cannot be auto-repaired by 7-Zip |
| Unicode filename support | Full Unicode (UTF-16) filenames for entries within the archive |
| Maximum theoretical size | Up to 16 exabytes (2⁶⁴ − 1 bytes) per archive and per individual file |
| Solid archive support | Solid compression mode (multiple files compressed as a single stream) is supported and can span across split volumes |
| Self-extracting (SFX) support | The split archive can be packaged as a self-extracting executable; the .7z.001 file remains the first volume |
| Released | Multi-volume (split) 7z support in 7-Zip; .7z.NNN volume naming |
| Open standard | Yes · royalty-free |
| Specification | www.7-zip.org |
7Z.001 conversions
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