RAR Files
The RAR File Format Explained
RAR is a proprietary archive format with its own header structure, versioning, and optional features like solid compression and recovery records.
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RAR is not an open standard the way ZIP is — it's a proprietary format designed and maintained by RARLAB. Only RARLAB's software can create genuine RAR archives, though many third-party tools, including 7-Zip, can extract them thanks to reverse-engineered or published-enough details of the format.
RAR4 vs RAR5
RARLAB has revised the format over time, with the two versions readers most commonly encounter being what's informally called RAR4 and the newer RAR5. RAR5 changed some internal details, including the header format and default encryption approach, compared to RAR4. Older extraction tools may not support RAR5 archives, which is a common reason a seemingly valid archive fails to open in outdated software.
Structure of a RAR archive
| Component | Purpose |
|---|---|
| Main header | Identifies the archive and stores global flags, such as whether it's part of a multi-volume set |
| File headers | One per stored file, holding the name, size, timestamp, and compression method |
| Compressed data blocks | The actual compressed bytes for each file or, in a solid archive, for the combined stream |
| Recovery record (optional) | Extra redundant data that can help repair minor archive corruption |
| End-of-archive marker | Signals where the archive's data ends |
Solid archives
A solid archive compresses all its files as one continuous data stream rather than compressing each file separately. This generally improves compression on collections of many small, similar files, but it means extracting a single file may require processing data earlier in the stream too. See RAR compression explained for more on how this affects speed.
Recovery records
WinRAR can optionally add a recovery record when creating an archive — extra redundant information that later lets a repair tool reconstruct minor damage, such as a few corrupted bytes from a bad download. It isn't a full backup and can't fix major corruption, but it helps with small transmission errors. See corrupted RAR file for repair steps.
Dictionary size
Compression algorithms like RAR's use a "dictionary" — a window of recently seen data used to find repeated patterns. A larger dictionary size can find more distant repetitions and sometimes compress better, at the cost of using more memory during compression. Dictionary size is one of the settings exposed in WinRAR's compression options.
Licensing and who can create RAR archives
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Install the archive tool and apply the steps from this guide on your own files.
Frequently asked questions
Is RAR an open format like ZIP?
No. RAR is proprietary to RARLAB. ZIP, by contrast, is a widely documented open format supported natively by many operating systems. See [ZIP vs RAR](/zip-vs-rar).
Why won't my archive tool open a RAR5 file?
Older extraction software may predate RAR5 support. Updating the extractor or using a current tool such as [WinRAR](/winrar) usually resolves it.
Does a recovery record make a RAR file bigger?
Yes, slightly, since it adds redundant data specifically to help repair minor corruption later.
Related guides
- How RAR Compression Actually WorksRAR compression shrinks files by finding and eliminating redundant patterns in the data — how much it helps depends heavily on what kind of file you're compressing.
- What Does the .RAR File Extension Mean?The .rar extension marks a file as a RAR archive, but you'll also see .r00, .part1.rar, and .rev variants used for split and recovery volumes.
- WinRAR vs 7-ZipWinRAR and 7-Zip are the two archive tools people ask about most on Windows. Here is how they actually differ, feature by feature.
- How to Fix a Corrupted RAR ArchiveA corrupted RAR archive can sometimes be repaired, and sometimes can't. Here's how to test one, what recovery tools actually do, and when re-downloading is the real fix.
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