The SpecialVersions_x64.zip and x32.zip packages contain mfakto.exe files compiled for special purposes: mfakto-64k : A binary optimized for 64k L1 cache. This is useful for most AMD CPUs, but also for Intel CPUs when going to high SievePrimes values (>100k). mfakto-var : Compiled to allow SieveSize configuration via mfakto.ini. Most useful for testing which SieveSize is optimal, but 1-3% slower sieving than the fixed-size compiled files (for the same SieveSize). mfakto-pi : For each block, the OpenCL performance counters are read and displayed. This allows for accurate measuring of transfer and kernel execution speed. Intended for performance tests. Apart from these settings, these binaries are the same as the corresponding normal package, which is optimized for 32k L1 cache (most Intel CPUs).