BOINC's credit system is based on a 'reference computer' that can do

• 1 billion floating-point multiplies per second
• 1 billion integer multiplies per second
• 4 billion bytes per second of traffic to and from main memory (sequential, half reads and half writes)

Some BOINC projects grant credit only after results have been validated.

Each project maintains two types of credit:

• Total credit: The total number of Cobblestones performed.
• Recent average credit: The average number of Cobblestones per day performed recently. This average decreases by a factor of two every week, according to algorithms given below.

Both types of credit (total and recent average) are maintained for each user and host.

Leader boards

Possible future improvements

• Ideally, credit should reflect network transfer and disk storage as well as computation. But it's hard to verify these activities, so for now they aren't included.
• Eventually projects will develop applications that use graphics coprocessors or other non-CPU hardware. Credit should reflect the usage of such hardware. To accomplish this, we will need to let projects supply their own benchmarking functions. This will also handle the situation where a project's application does e.g. all integer arithmetic.

How 'Recent Average Credit' is computed

",htmlspecialchars("

// Update an estimate of \"units per day\" of something (credit or CPU time).
// The estimate is exponentially averaged with a given half-life
// (i.e. if no new work is done, the average will decline by 50% in this time).
// This function can be called either with new work,
// or with zero work to decay an existing average.
//
void update_average(
    double work_start_time,       // when new work was started
                                    // (or zero if no new work)
    double work,                    // amount of new work
    double half_life,
    double& avg,                    // average work per day (in and out)
    double& avg_time                // when average was last computed
) {
    double now = dtime();

    if (avg_time) {
        double diff = now - avg_time;
        double diff_days = diff/SECONDS_PER_DAY;
        double weight = exp(-diff*M_LN2/half_life);
        avg *= weight;
        avg += (1-weight)*(work/diff_days);
    } else {
        double dd = (now - work_start_time)/SECONDS_PER_DAY;
        avg = work/dd;
    }
    avg_time = now;
}

"),"