As noted in the introduction, a growing trend toward imbalance is present in the basic underlying technology of cpus vs memory, and it is of significant interest to see how this has manifested itself in actual products. Based on the STREAM results and some estimates of the performance of older machines, some historical trends in machine balance are represented in Table 1 for several major vendors.
Table 1: Historical changes in machine balance for several important computer vendors. Memory bandwidth and Peak FP rate are estimated for the VAX 11/780 and 8088-based IBM PC, and measured for all other cases.
The shift in machine balance is clear for all lines except the IBM RS/6000, where increasing bus width and an extra load/store unit on the Power2 processor have managed to keep the balance constant, but only at a significantly increased price level.
Based on the estimates of 80% per year improvement in microprocessor speed , and 7% per year increase in memory speed , we might expect a machine balance increasing at 73% per year. The data from Table 1 are compared with theoretical estimates in Figure 8, and a remarkable agreement with this expectation is seen.
Figure 8: Historical changes in machine balance for several important computer vendors. Memory bandwidth and Peak FP rate are estimated for the VAX 11/780 and 8088-based IBM PC, and measured for all other cases. The straight line is a theoretical estimate based on trends in the underlying technology.
From 1990 to 1995, the DEC, IBM PC, and SGI trends in machine balance follow the 73% per year curve quite closely.