This is an interesting question: How far off was the Cyrix FasMath 387+ FPU from that of the Intel 486DX of the same clock speed. Plans for the Ultimate 486 Benchmark Comparison will include this analysis and these benchmarks. Actually, I was going to include all PGA 132 chips in the comparison as well as some results using those PGA-132 to PGA-168 486 adapter kits.
From my previous testing, a really fast 386 system, one with a 486SXL-40 on a high-end motherboard has ALU performance between a 486 DX25 and 486 DX33, but closer to the 25. If you run the 486SXL at 50 MHz, then you get to about a DX33. As for FPU, I suspect half that, but would need to run some tests. Certainly not an order of magnitude, which is 10-fold). Unfortunately, I do not own an ISA-only 486 motherboard to run these tests. I suspect VLB-based and PCI-based motherboards would be faster than an ISA only 486, even if expansion cards are restricted to the ISA bus.
If you don't want to overclock your 386's bus to 50 MHz, I have discovered that some motherboards really shine with the SXL2-50 at 2x25 MHz, so much that the performance is about the same as a 1x50 MHz system. Other motherboards, I found, do not shine at 2x25 MHz. I will report on this later in the forum when I have finished this testing.
kixs wrote:486 uses next generation FPU. It's only normal to be faster. Like Pentium runs in circles around 486 😉
It would be interesting to disable one of the parallel ALU units of the original Pentium chips to see how much impact that had.
Anonymous Coward wrote:I'm very interested to know how 387 vs 487 (not the 487sx) performs on a clock for clock basis.
Are there any performance differences between the IIT 487 and IIT 387 chips?
e.g. http://www.chipdb.org/img-iit-4c87dlc-40-alum … -print-2916.htm vs. http://www.chipdb.org/img-iit-3c87-40-diff-print-2907.htm ? Or are those 487 chips just for some motherboards which have compatibility issues with the 387 chips when a DLC CPU is used?
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