Cobblestones
The basis for the BOINC credit system is the cobblestone named after Jeff Cobb of SETI@home. The basis of the system is the concept that 200 cobblestones would be claimed for one day of work on a computer with the following specifications:
- 1,000 double-precision MIPS based on the Whetstone benchmark.
- 1,000 VAX MIPS based on the Dhrystone benchmark.
The actual computational difficulty needed to run a given work unit is the basis for the number of credits that it should be granted. The BOINC system allows for work of any length to be processed and have a user claim identical amounts of credit.
To achieve this BOINC uses benchmarks to measure the speed of a system and in combination with the amount of time it required for a work unit to process can “guess” at the amount of credit it should receive. Since systems have many variables including the amount of RAM, the processor speed, and specific architectures of different motherboards and CPUs, there can be wide discrepancies in the number of credits that different computers believe that each work unit requires to process.
Most projects require a consensus be reached by having multiple hosts return the same work unit. If they all agree then the credit is calculated and all hosts receive the same amount regardless of what they asked for. Each project can use their own policy depending on what they see is best for their specific needs. In general the top and bottom claimed credits are dropped and an average of the remaining is taken.
Read more about this topic: BOINC Credit System