Advanced compression parameters
Usually there is no need to change settings in this dialog and it is safer to allow WinRAR to select optimal parameters automatically. Please note that improper use of this dialog may lead to very serious performance and compression loss, so change its parameters only if you clearly understand what you do.
Most of settings below are supported only by RAR 4.x archive format. None of these settings are available for ZIP. Only delta compression and 32 bit executable compression can be enabled for RAR 5.0 archives.
This dialog contains the following options.
Text compression allows to improve the compression ratio for plain text data, but its compression and decompression speed also as ability to utilize several processor cores are much worse than in general compression algorithm. So the default state for this option is "Disable". You can change it to "Auto" to allow WinRAR to select this algorithm automatically for suitable data. "Force" applies the text compression algorithm to all data, but be prepared to slower archiving and extracting if using this option.
Set the prediction order of PPM algorithm (the kernel of RAR text compression). Allowed values are 2 - 63. Usually a higher value slightly increases the compression ratio of redundant data, but only if enough memory is available to PPM. In case of lack of memory the result may be negative. Higher order values decrease both compression and decompression speed. If this field is set to 0, WinRAR will choose the order automatically.
Memory in megabytes allocated for PPM (can be 1-128). Higher values may increase the compression ratio, but note that PPM uses an equal memory size both to compress and decompress, so if you allocate too much memory when creating an archive, other people may have problems when unpacking it on a computer with less memory installed. If this field is set to 0, WinRAR will choose the memory size automatically.
In "Auto" mode WinRAR will decide when to use the audio compression depending on source data and only if "Normal", "Good" or "Best" compression method is selected. "Force" applies the audio compression algorithm to all compressing data. It makes sense only if you are sure that all compressed files completely consist of raw audio data. "Disable" prohibits the audio compression algorithm at all.
The audio compression is designed to process raw audio data like WAV files. It does not increase compression of already compressed audio files like MP3.
Number of byte channels (can be 1 - 31).
WinRAR splits multibyte channels to bytes, for example, two 16-bit audio channels are considered by WinRAR as four channels one byte each. If this field is set to 0, WinRAR will detect a number of channels automatically.
In "Auto" mode WinRAR will decide when to use the true color compression depending on source data and only if "Normal", "Good" or "Best" compression method is selected. "Force" applies the true color compression algorithm to all compressing data. It makes sense only if you are sure that all compressed files completely consist of true color (RGB) data. "Disable" prohibits the true color compression algorithm at all.
The true color compression is designed to process raw RGB based color data like 24-bit BMP files. It does not increase compression of already compressed files like JPG.
Allow WinRAR to improve compression of 32-bit Intel executable files using an algorithm specially optimized for this data type.
Allow WinRAR to improve compression of 64-bit Intel executable files using an algorithm specially optimized for this data type.
Allow WinRAR to improve compression of structured table data using an algorithm specially optimized for this data type.
Reset all options of this dialog to default values.
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