Chapter 52 ½ The IBM System/360, System/370, 3030, and 4300: A Series of Planned Machines That Span a Wide Performance Range 891
times for certain fixed work. Solomon [1966] observed Grosch's law to hold for Models 30, 40, 50, 65, and 75. This line is drawn in Fig. 39 for C(price.average). Considering Models 20, 25, 44, 85, and 91, a line with a less steep slope might fit the points better. If we consider C(price.minimum), g> 2; considering only Pc, a g = 1 might be appropriate (see Fig. 39) for which the Pc power/price is essentially constant with cost.
C(price.min)/C(price.avg): = c.min.C/avg.C = ~ 0.47, the ratio of the smallest computer configuration to an average configuration
Pc(price)/C(price.avg): = c.Pc/c.avg.C = ~ 0.23, the ratio of processor to computer price
The price for the System/370 series is based on purchase price. Figure 40 gives the relative computing power versus price for a Pc
with average Mp size. Again, the price/power ratio is almost constant with at most a 3:1 variation. The best-performing models seem to be the replacement models (i.e., the 138 for the 135, the 148 for the 145). Presumably, newer technology and packaging yielded an increase in performance. Models 165 and 168 are clear price/performance leaders.
Figure 41 plots the relative performance to purchase price for various processor models and minimum to maximum memory size. Grosch's law is also plotted. It appears that the System/370 series follows a power law with g ~ 1.6.
