Use known start of the file for stored archives (hex):

If your archive contains a single encrypted file, and this file is stored (i.e. not compressed), using that option is a solution to get much better recovery speed. You have to know 1 to 4 bytes in the beginning of the file. There are many well-known signatures such as, for example, 'MZ' (hex: 4D 5A) for executable files, 'PK' (hex: 50 4B 03 04) for ZIP files, D0 CF 11 E0 (hex) for OLE compound documents (like MS Word/Excel files), etc.

Always use WinZIP optimized attack engine if probability is greater than XX%:

If an archive was created in WinZIP (or another Windows-based ZIP tool based on the same sources) and contains at least five encrypted files, the speed of brute-force attack can be improved threefold. ARCHPR attempts to automatically detect such files using heuristics. The program calculates the probability value, which is based on the number of files in the archive and other factors. If it is greater than 50%, ARCHPR suggests using the optimized attack when you start the recovery process. You can set this option for your convenience, so the optimized engine will or will not be used automatically. 85% is a good suggested value to use.

Mask symbol:

Used for the Mask attack.

Use code optimized for:

(Non-MMX processors / Intel PII/PIII/Celeron / AMD Athlon / Intel P4 SSE2 / Intel Core/Core2): overrides automatic CPU detection and forces ARCHPR to use code specially optimized for the given CPUs.