Common sense guides computer design
Since its engineering, common sense is valuable
In making a design trade-off, favor the frequent case over the infrequent case
E.g., Instruction fetch and decode unit used more frequently than multiplier, so optimize it 1st
E.g., If database server has 50 disks / processor, storage dependability dominates system dependability, so optimize it 1st
Frequent case is often simpler and can be done faster than the infrequent case
E.g., overflow is rare when adding 2 numbers, so improve performance by optimizing more common case of no overflow
May slow down overflow, but overall performance improved by optimizing for the normal case
What is frequent case and how much performance improved by making case faster => Amdahl’s Law