As quad core CPUs are becoming mainstream and more affordable, users pay more attention to multi-core efficiency. The primary target in the development of WinRAR 4.20 has been improving this efficiency.
The ZIP Code has been rewritten and is now using similar techniques as in RAR compression, which is making WinRAR 4.2 ZIP compression faster than WinRAR 4.11, even in single-core mode by about 70%. By utilizing the multi-core support in 4.20 ZIP, can be up to 3 times faster than 4.11.