First post, by feipoa
- Rank
- l33t++
I decided to run a quick comparison of the various 386 FPU types on a ALi1429-based 386 system. I have the FSB set to 33 MHz and am using a TI 486SXL for all FPU measurements except for the Intel RapidCAD, which requires the RapidCAD CPU. In the chart below, the winner, but not by much, was the grey-top Cyrix FasMath. You will notice that it is a few points faster than the black-top versions or the DLC versions of the same cahp. Cyrix likely added some DLC compatibility features to the FasMath, with consequence being marginally reduced performance. Conversely, the IIT 3C87 grey ceramic top chip (126 a.u.) was slower than its counterparts with either gold caps, black plastic caps, or with the DLC marking (135 a.u.). The ULSI DX and DLC chips had the same result and were a little slower than the IIT chips.
At rock bottom was the Intel i387DX. I am left to wonder if Intel intentionally made it perform poorly to encourage RapidCAD or next generation chip sales. You will notice that the RapidCAD beats all the single-clock competitors, though a DRx2 or SXL2 at 66 MHz using a basic black-top FasMath will still outperform the RapidCAD, at least inasmuch as Landmark is concerned.
What I found most intriguing was the ULSI Math-Co DX-2 66 MHz FPU. With an incredible 2x clock multiplier, it performed just barely worse than the single clock Cyrix FasMath grey-tops, and only a smidge above the FasMath black-tops. What is going on here? The ULSI DX2 at 66 MHz performs only 12% faster than the ULSI DX at 33 MHz. Does a clock doubled FPU need a clock doubled CPU to take advantage of its doubled clock rate? The ULSI DX-2 at 66 MHz scored 145 a.u. while the ULSI DX at 33 MHz scored 130 a.u. This had me wondering, so I also ran these chips with a clock doubled SXL2 at 66 MHz.
With the clock doubled SXL2 at 66 MHz, the ULSI DX2 also at 66 MHz rounded the top with 225 a.u., while a 33 MHz FasMath black-top scored 209 a.u. Why doesn't the ULSI DX2 at 66 MHz yield significantly better results compared to the FasMath at 33 MHz? Is the CPU the bottleneck? Single-clocked FPUs, such as the FasMath and ULSI DX, both, show a 46% increase in performance at 33 MHz when using a clock doubled CPU (SXL2-66) compared to a clock singled CPU (SXL-33). The ULSI DX2 showed a 55% boost in going from the SXL-33 to the SXL-66. For the case of the SXL2-66, the increase from single-clock ULSI DX to doubled clocked ULSI DX2 was only 18%, but at least it was faster than the 12% increase for the case of SXL-33 for ULSI DX to ULSI DX2. Why is this?
The one other courisity was the C&T Super Math Chips. I was surprised to see it neck and neck with the Cyrix FasMath. I wonder how these chips were priced comapred to the competition...
Data table follows
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