PowerLogix PowerForce G3 250/250 Update

Macs Only!'s review of this CPU upgrade card mentioned that one should be able to increase the CPU speed further if the CPU/cache speed ratio were raised to 3:2 or 2:1 from 1:1, i.e. lowering the backside cache speed.

The highest stable CPU speed attained with a 1:1 ratio was 292.4 MHz from the 250 MHz G3 CPU at a 45 MHz system bus speed in my PowerComputing PowerBase 180. The PowerBase has a rated bus speed of only 40 MHz. I have now run my PowerBase at 292.4/45/1:1 (i.e. CPU Speed/System Bus Speed/CPU:Cache Speed Ratio) for 10 weeks with the PowerForce card--it hasn't missed a beat. With higher CPU/cache ratios than 1:1 being the norm for most G3 CPU's on the market, I ran some additional trials using MacBench 4.0. Since I am now using Mac OS 8.1, I re-ran the tests for the 292.4/45/1:1 setup. Here are the processor (integer math) and floating point (fractional math) scores for the highest CPU speed for each system speed and CPU/Cache ratio that started up and ran the MacBench tests without a crash or freeze:

MacBench 4.0 Scores for Various CPU, Bus and Cache Speeds*

CPU (MHz)	System Bus (MHz)	CPU/Cache Speed Ratio	MacBench 4.0 Scores (Processor/Floating Point)
292.4	45.00	1:1	1077/934
300.0	40.00	2:1	1011/946
300.0	40.00	3:2	1044/954
315.0	45.00	2:1	1060/994
315.0	45.00	3:2	1098/1002
314.3	48.36	2:1	1066/995
314.3	48.36	3:2	1100/995
325.0	50.00	2:1	1098/1025
325.0	50.00	3:2	1131/1031

*Mac OS 8.1, LibMotoSh and Virtual Memory (1 MB) on in a PowerBase with 56 MB RAM

The MacBench scores for some combinations are significantly higher than for the 292.4/45/1:1 setup that I have been using. However, in short term usage the 325 MHz CPU and 50 MHz bus speed combinations demonstrated instabilities. The scores are nearly identical for system bus speeds of 45 and 48.36 MHz, so I decided to take the safer route and conduct a long term use test on the 315/45/3:2 configuration. It is faster by several seconds (53 vs 56) at loading Virtual PC Windows 95 than the 292.4/45/1:1 combination. I never imagined that my PowerBase would ever run at over 300 MHz with MacBench CPU scores around 1100--amazing! Check out Macs Only!'s full review. Stay tuned for the long term results.