GIMPS type of work
You have the choice of 4 main types of work units (WU) you can do for the project. The client can also do other types of work as well, but they are outside the scope of this page (for more information see the readme.txt that comes with the client). The different types are listed in the order that they are performed on an exponent.
Factoring of a prime number (exponent) candidate
Trial factoring is a pre check of a candidate exponent. These work units take the least time and are given out by the server according to your CPU speed. They may go through several iterations of bit length before clearing and getting sent to a fast machine for the more intensive Lucas-Lehmer testing. This is best for low-end PIIIs and Athlons. There is no chance of finding a prime through factoring.
Lone Mersenne Hunters is a project trial factoring candidates outside the normal range of exponents.
This is a different type of factoring than trial factoring. Unlike TF, the P-1 factorization method is not done a single bit level at a time. Rather bounds are used. The more memory available the greater the chance of finding a factor. P-1 factoring takes longer per single unit than TF, but the chance of finding a factor (especially large factors) are greater (per each WU).
(First time) Lucas Lehmer (LL) testing on a prime candidate
Lucas-Lehmer is the actual primaltity test; the chance of finding a prime candidate is currently somewhere on the order of one in several hundred thousand. Pre factoring is designed to ensure that no time is spent on lengthly LL work when a relatively small factor is present. There are several variations of this currently available:
- Standard (take the next exponent the server hands out)
- 10 million + digit Mersenne Prime testing (specifically request an exponent that will yield a number at least 10 million digits long)
- World Record (request an exponent that will yield a number larger than the current record)
- 100 million digit (request an exponent that will yield a number with at least 100 million digits, these will take around 2.5 to 3 years to test on the fastest consumer hardware, as of May 2009). The 100 million digit level is the level that could win the next Electronic Frontier Foundation prize.
Double checking a prime candidate
Double checking is done to work units which have cleared one round of Lucas-Lehmer testing. This verifies that the LL test has concluded correctly and ensures that the computer that performed the first LL test performed to specifications. These are small to medium units, PIII, Athlons and low end P4s turf here. Basically this is a Lucas-Lehmer test, but the exponent size is smaller than for the current first time primality test range because a few years typically pass between the first LL test of an exponent and it's doublecheck, by which time GIMPS has moved on to larger exponents.