Originally Posted by rogue Good news. I found and fixed the bug with cksieve (stupid x86 asm). Here is a complete list of changes: Code:  Add an internal flag that guarantee that suspends all but one Worker when processing the first chunk of primes. This is used to improve performance when there is a high factor density for low primes. This will also suppress any on screen reporting or checkpointing until that chunk is processed. Fix issue in computing CPU utilization. Changed -c (chunksize) option to -w (worksize). Change output to use shorter notation for min and max primes. cksieve - Fixed. gfndsieve - Enable the flag mentioned above. fbncsieve - Enable the flag mentioned above. fkbnsieve - Added, but not tested. Visit my page to get the link to d/l the latest source and Windows builds.