Sieve applications for CPUs have been released as beta/test applications. Most of the config settings do not apply for CPUs but you will find that adjusting the lut_size and especially the sieve_size will affect both the processing speed and RAM required. (e.g. lut_size=20 and sieve_size=31 uses 200MB per app whereas the stock settings of lut_size=12 and sieve_size=26 uses 9MB per app but runs about 30% slower).