Switch -MD<n> - select dictionary size

This switch allows the selection of dictionary size <n> in KB. <n> must be 64, 128, 256, 512, 1024, 2048, 4096 or a letter 'a', 'b', 'c', 'd', 'e', 'f', 'g' accordingly. The default sliding dictionary size in WinRAR is 4096 KB.

The sliding dictionary is a special memory area used by the compression algorithm. If the size of the file being compressed (or the total files size in the case of a solid archive) is greater than the dictionary size, then increasing the dictionary size will generally increase compression ratio, decrease packing speed and increase memory requirements. Unlike compression, extraction speed is unaffected by dictionary size.

WinRAR can reduce the dictionary size if it is significantly larger than the size of the source data. It helps to reduce memory requirements without decreasing compression.

ZIP archives always created using 32KB dictionary. Larger values cannot be used because of restrictions of ZIP format.

The dictionary size may also be selected through the "Dictionary size" list in the Advanced compression parameters dialog.

Example

create a solid archive stuff using a 512KB dictionary and the best compression method

WinRAR a -md512 -m5 -s stuff