What are the benefits: RAR4 vs RAR5?
There are millions of RAR files in the world and most of them have been compressed with the algorithm RAR4, which can open almost all decompressors and almost all versions of WinRAR. WinRAR Version 5 introduces a higher standard, RAR5.
For starters, RAR5 increases the compression dictionary size to 1GB (in the 64-bit version). The larger the dictionary, which stores the repeatable parts of a file, the better the compression, but only for huge files.
The default size of the RAR compression dictionary is 32MB, a much lower figure. So when would you need to use large dictionary sizes? When you have huge files that you aren’t going to share, such as when you make a back up.
Another important change is the new recovery log. RAR5 format is much more resistant to damage than RAR4, but only with a log size equal or greater than 5% of the file, even if it’s corrupted.
Finally, with RAR5 you can encrypt your data with a 256-bit AES algorithm. It’s certainly not the strongest encryption on the market, but it is very, very robust. The U.S. government uses it to protect its Top Secret content.
Mini-comparison: RAR5 vs. 7-Zip vs. RAR4
In several tests, RAR5 has outperformed 7-Zip in terms of speed and compression ratio. For example, in a test published in Hyperspin, WinRAR 5 decompressed a 5GB image in two minutes compared to almost six minutes for 7-Zip.
We did a quick test comparing RAR5, RAR4 and 7-Zip (LZMA and LZMA2). The machine used was a Dell Precision Workstation 490 with CPU Intel Xeon 5130 (dual-processor quad-core), 16GB of RAM and Windows 8 Pro 64bit.
The file contained 104 different file types (documents, videos, images and uncompressed music) in ten folders, occupying a total area of 528.031.744 bytes in the NTFS partition. Source and destination were the same ATA hard drive.
Three default options were used: fastest, most powerful and normal. The only thing that changed was the size of the dictionaries to match, as far as possible, those used by RAR5 (apart from RAR4, which was limited to 4mb).
Starting with the obvious: RAR algorithm speed is impressive both in RAR4 andRAR5. Bear in mind that the normal RAR5 level uses 32MB dictionaries, which increased compression times considerably.
7-Zip results weren’t great. In the case of LZMA, which is the algorithm 7-Zip uses by default, the CPU is hardly used, whereas LZMA2 doesn’t have this limitation. But even using eight multithreaded cores couldn’t beat RAR4.
The results of compression, which can be tentatively drawn from the sample used, show some advantage to using RAR over 7-Zip, but they’re not very significant.
Can RAR5 be used now?
Absolutely. To do this you have to choose the option RAR5 to compress a new file from WinRAR 5.0. The default dictionary size is 32 megabytes.
Why can’t I unzip RAR5?
Files compressed with the algorithm RAR5 are still very new and, can only be opened by WinRAR 5. We tested several of the most popular decompressors, such as 7-Zip and IZArc, and we haven’t managed to open RAR5 files.
Although RAR isn’t an open source format, WinRAR distributes the source code of the UnRAR utility, which is free and only for command lines. On the same page the RAR5 format specifications are available.
Whether other decompressors will open RAR5 files depends on how fast they adopt the new standard. In the case of 7-Zip, Igor Pavlov, the lead developer, has said that adding support for RAR5 “isn’t a priority”.
What version of RAR should you use?
Right now, for compatibility reasons, our recommendation is to use RAR4, which WinRAR offers by default. To share RAR5 files it’s best to wait until the format gets a bit more popular, or create a self-extracting file.
Which compression format are you going to use?