What is the 0 file format?
A .0 file is the first volume in a numbered split-archive series. Files with the .0 extension are most commonly created by Hacha - a Spanish-language file-splitting utility for Windows - or by HJSplit, which uses the same numbering convention. Once a ZIP archive, large video, or other file is divided into smaller volumes, the software allocates a sequential number to each volume. The .0 extension is allocated to the first (zero-indexed) volume of the series; a typical name looks like filename.zip.0, with filename.zip.1, filename.zip.2, and so on following it.
A .0 part carries no dedicated header - it is simply the opening raw slice of the original file. To reassemble the volumes, open the .0 file in Hacha or HJSplit, or join them on the command line: copy /b filename.zip.0+filename.zip.1 output.zip on Windows, or cat filename.zip.* > output.zip on Linux/macOS.
Security & safety
RISK: MEDIUMA .0 part is opaque until rejoined, so treat unexpected sets with care: once joined you may get an executable or archive that could contain malware - scan the rejoined file before running it, especially if it came by e-mail or from an untrusted download. The .0-specific gotcha is completeness, not security: if any numbered part is missing, the set cannot be rejoined and the missing bytes can't be recovered - you must obtain the full series. Also get Hacha/HJSplit from their official sites, since download portals sometimes bundle adware.
Format details
in a nutshell- Rotated log / app backup (.0) - Some applications use .0 as a generic numbered data, log or backup file (e.g. app.log.0) that has nothing to do with file splitting.
Programs that open 0 files
Windows4 apps
Hacha
Free Made the file? Open Hacha, choose Join (Unir), point it at the .0 (and its .hac if present); it rebuilds the original. Free, still updated (v3.5.0, 2025). 
7-Zip
Open-source For HJSplit-style numbered sets: put all parts in one folder and open the .001/.0 - 7-Zip can join split files. (May not read Hacha's .hac scheme - use Hacha then.) 
HJSplit
Free Free splitter/joiner. Choose 'Join', select the .0 part; it concatenates .0/.1/.2… back into the original. Works for generic numbered parts.
Command line (copy /b)
Built-in If parts are plain raw slices in order: 'copy /b file.0 + file.1 + file.2 original.zip' rejoins them. Only works when there's no per-part header. 
macOS1 app
HJSplit (Mac) / cat command
Free Use HJSplit's Mac build, or in Terminal run 'cat file.0 file.1 file.2 > original' for raw slices, then open the rejoined file. 
Linux1 app
cat (command line)
Built-in For raw split parts: 'cat file.0 file.1 file.2 > original' joins them in order; then open the result with the right app. Technical details
deep spec| Format type | First (zero-indexed) volume of a split multi-part file |
| MIME type | application/octet-stream |
| Magic bytes | None - contains the raw opening bytes of the original file, not a dedicated header |
| Typical naming pattern | basename.ext.0 (e.g. movie.avi.0, backup.zip.0) |
| Volume numbering | Zero-indexed: .0 is part 1, .1 is part 2, and so on |
| Part identification method | Sibling files (.1, .2 …) sharing the same base name; not identifiable by content alone |
| File structure | Raw binary slice - no wrapper header or footer of its own |
| Primary creator | Hacha (Windows freeware, Spanish-language UI, maintained through v3.5.0 as of late 2025) |
| Other common creator | HJSplit (Windows, Linux, macOS); also producible with copy /b or cat |
| Reassembly - Windows | copy /b part.0+part.1+... output.ext at the command prompt |
| Reassembly - Linux/macOS | cat part.0 part.1 ... > output.ext (or cat part.* > output.ext if numerically ordered) |
| Encoding | Binary (raw bytes, no text encoding) |
| Maximum part count | Unlimited in principle - constrained only by available digit width in the numbering scheme |
| Typical use case | Splitting large archives or media files to fit FAT32 size limits, email attachments, or FTP segment transfers |
| Released | Numbered split-part naming predates the web; Hacha released c. 2000 (still maintained, v3.5.0 Oct 2025) |
0 conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about 0 files.
