Hardware Reference
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SPEC is a consortium of competing companies, each company might have their own favorite
set of weights, which would make it hard to reach consensus. One approach is to use weights
that make all programs execute an equal time on some reference computer, but this biases the
results to the performance characteristics of the reference computer.
Rather than pick weights, we could normalize execution times to a reference computer by
dividing the time on the reference computer by the time on the computer being rated, yielding
a ratio proportional to performance. SPEC uses this approach, calling the ratio the SPECRatio.
It has a particularly useful property that it matches the way we compare computer perform-
ance throughout this text—namely, comparing performance ratios. For example, suppose that
the SPECRatio of computer A on a benchmark was 1.25 times higher than computer B; then
we would know:
Notice that the execution times on the reference computer drop out and the choice of the
reference computer is irrelevant when the comparisons are made as a ratio, which is the ap-
proach we consistently use. Figure 1.17 gives an example.
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