Switch -MC<par> - set advanced compression parameters
This switch is intended mainly for benchmarking and experiments. In the real environment it is usually better to allow WinRAR to select optimal parameters automatically. Please note that improper use of this switch may lead to very serious performance and compression loss, so use it only if you clearly understand what you do.
It has the following syntax:
-mc[param1][:param2][module][+ or -]
where <module> is the one character field denoting
a part of the compression algorithm, which has to be configured. It
may have the following values:
| A | audio compression; |
| C | true color (RGB) data compression; |
| D | delta compression; |
| E | x86 executable compression; |
| T | text compression. |
RAR 5.0 archive format supports only 'D' and 'E' values.
'+' sign at the end of switch applies the selected algorithm module to all processed data, '-' disables the module at all. If no sign is specified, WinRAR will choose modules automatically, based on data and the current compression method. Switch -mc- disables all optional modules and allows only the general compression algorithm.
<Param1> and <Param2> are module dependent parameters described below.
<Param1> is a 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.
<Param2> is ignored.
<Param1> and <Param2> are ignored.
The text compression algorithm provides noticeably higher compression on plain text data. But it cannot utilize several CPU cores efficiently resulting in slower compression time comparing to general algorithm in multicore and multiprocessor environment. Also its decompression speed is much slower than in general algorithm regardless of CPU cores number. This is why the text compression is disabled by default. You can specify -mct switch to allow WinRAR to select this algorithm automatically for suitable data. Switch -mct+ will force use of the text compression for all data.
Switch -mct can also include <Param1> and <Param2>, so its full syntax is -mc[param1][:param2]t[+ or -].
<Param1> is the order of PPM algorithm (can be 2 - 63).
<Param2> is memory in megabytes allocated for PPM (1-128).
PPM uses the 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 decompressing it on a computer with less memory installed. Decompression will be still possible using virtual memory, but it may become very slow.