If, for example, we consider that performing a floating point operation on a scalar machine may require an average of three instructions, then one MFlops may imply three Mips. For example, the CRAY YMP has a cycle time of 6 nano sec. This is generally a peak rate, and operations are done in full precision. In other words, the manufacturer guarantees that programs will not exceed these rates, which amount to a kind of speed of light for a given computer. More important than peak performance for the newer massively parallel machines is scalability.
Sustained performance is average performance.
We will speak of vector performance here, even though the discussion could be broadened. Typical vector rates attained from high-level compiled source code have been found to be significantly lower than the peak theoretical rates. It is fairly typical to find sustained rates to approach 50 percent of the peak rate. For example, the CRAY J90 computer with 32 processors reports a sustainable application performance of 2 to 3 GFlops. Click here for more information.