In this paper, for the problem of minimizing the makespan on two unrelated parallel machines we compare the quality of preemptive and non-preemptive schedules. It is known that there exists an optimal preemptive schedule with at most two preemptions. We show that the power of preemption, i.e., the ratio of the makespan computed for the best non-preemptive schedule to the makespan of the optimal preemptive schedule is at most 3/2. We also show that the ratio of the makespan computed for the best schedule with at most one preemption to the makespan of the optimal preemptive schedule is at most 9/8. For both models, we present polynomial-time algorithms that find schedules of the required quality. The established bounds match those previously known for a less general problem with two uniform machines. We have found one point of difference between the uniform and unrelated machines: if an optimal preemptive schedule contains exactly one preemption then the ratio of the makespan computed for the best non-preemptive schedule to the makespan of the optimal preemptive schedule is at most 4/3 if the two machines are uniform and remains 3/2 if the machines are unrelated.

在本文中，对于最小化两台不相关并行机器上的制造时间的问题，我们比较了抢占式和非抢占式调度的质量。已知存在最多两个抢占的最优抢占调度。我们表明抢占的力量，即为最佳非抢占调度计算的制造期与最佳抢占式调度的制造期之比最多为 3/2。我们还表明，为最多一个抢占的最佳调度计算的 makepan 与最佳抢占调度的 makepan 之比最多为 9/8。对于这两个模型，我们提出了多项式时间算法，可以找到所需质量的时间表。已建立的界限与先前已知的两个统一机器的不太普遍的问题相匹配。