Guest Review - RailGun G3 250/166/1MB BSC in a 7500 (7600, 7300)

By Mychailo Toloczko August 4, 1998

Introduction

As Mike has already reviewed this card, I have tried to supplement his review by providing an expanded set of results. Using MacBench 4.0, I have looked at how all the main test scores vary with CPU speed and motherboard bus speed. As the card was extremely simple to install, nothing on the installation of the card is reviewed here. Just follow the instructions that come with the card.

Performance

Here are the specs of my machine: 7500 (VAL-4) 256 MB RAM two 2GB Atlas II drives (XP32275W) in a striped array Initio Miles PCI SCSI card, BIOS 1.03, PCI slot A1 IMS TwinTurbo M4, TT405 driver, PCI slot B1 4.0 MB disk cache VM off System 8.1 Speed Doubler 8.1 Conley SoftRAID 2.0.2 Standard HFS volume Monitor set to 1024x768 pixels and millions of colors For all the test results shown here, the backside cache was set to run at the speed of the CPU. Stability was not affected by the speed of the backside cache, ie, the machine would not run properly at a CPU speed of 320 MHz regardless of whether the BSC was set to run at 320 MHz (1:1) or 213 MHz (1.5:1). After each MacBench test, the machine was shut down, the CPU/motherboard bus speeds were adjusted, and then the machine was started. MacBench 4.0 scores vs motherboard bus speed Shown on the right are MacBench 4.0 scores at various CPU speeds. For each CPU speed, two sets of tests were performed, one at the lowest possible motherboard bus speed and the other at the highest possible motherboard bus speed. The percent difference in motherboard bus speed was 12.5% at the highest and 8% at the lowest. With the exception of the FPU score, the MacBench 4.0 scores were relatively insensitive to motherboard bus speed. A 12.5% increase in motherboard bus speed would yield only a few percent increase in disk and graphics scores, while the CPU score would be virtually unchanged. In testing this card, I found that higher CPU speeds could be reached when the motherboard bus speed was set at the low end of the range. For instance, the machine would not run properly at 293/293/45 (A=7, B=F), but it would run properly at 308/308/41 (A=9, B=3). It is worth mentioning that the disk and graphics subsystems on my machine are not on the motherboard, whereas a stock 7500 has both subsystems on the motherboard. I suspected that the sensitivity of the graphics score to motherboard bus speed may increase if the motherboard graphics subsystem were used instead of the Twin Turbo graphics card, so I switched to the onboard graphics controller and ran more MacBench 4.0 graphics tests. The results of these graphics tests are shown in the figure below. As with the Twin Turbo graphics card, I ran monitor at 1024x768 pixels, but since I only have 2 MB of onboard VRAM, the bit depth was limited to 16 bits, ie thousands of colors. As can be seen, variations in motherboard bus speed also had little effect on the graphics scores when using the on board graphics controller on a 7500. MacBench 4.0 scores vs CPU speed Shown in the figure at the right are the MacBench 4.0 scores plotted versus CPU speed. The motherboard bus speed was kept between 40-41.7 MHz for these tests. The CPU scores scales in a very linear manner with the CPU speed whereas the other test scores are somewhat less linear. For the most part, the disk score did plateau at about 590. The improvement in graphics score with increasing CPU speed shows that the graphics system is somewhat dependent CPU processing power. As the CPU issues the QuickDraw commands, the CPU is effectively part of the graphics system, so I think the increase in graphics score with CPU processing power makes pretty good sense.

Compatibility

The RailGun card appears to be completely compatible with my 7500 and both the installed PCI cards. I have not observed any unusual behavior attributable to a hardware conflict. Although I have heard a few reports that 7500's with G3 upgrade cards run more reliably with an L2 cache installed, I did not attempt to run the RailGun with the 256 KB L2 cache that was installed prior to purchasing the RailGun. Although the card runs fine at 300/300/40, for the time being, the card is set to run at 280/280/40 simply to have a comfortable margin of stability.

Feedback

I welcome your comments. Additional suggestions and comments you wish to share with others through the xlr8yourmac site are best sent to Mike.

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