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Which 387 math co-processor when using a 33MHz 486 upgrade chip?

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aaron7

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I've heard you don't want a slower clock speed math co-processor than your CPU clock speed.

Such as if you have a 386-20, you want a 20MHz 387 and not 16MHz.

So, I'm using a 486-33 'upgrade' CPU. But I can't seem to locate a 33MHz 387 to match it.

Would I be better off running no co-processor? I don't believe the Cyrix has it built in, does it?
 

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Unless a game or Windows 95 might, no. But I love maxing out my machines. Call it a strange addiction haha
 
Oh just saw the link, thanks! Was there a 40MHz by chance?
 
Some 386 mobos and coprocessors support running the CPU and the FPU at different speeds.
However, I wouldn't bother, 387 chips for 33 MHz aren't rare.
I've even seen chips marked "16-33 MHz" - I guess originally they were making separate 16, 20, 25, 33 chips, but later on, they improved the process so that all the chips were capable of 33 MHz, so they combined the entire line into one "16-33" product.
 
Thanks for doing the searching for me! One of those is a 486 upgrade chip, but out of the other three are they all the same functionality wise?
 
There were also 387DX co-processors branded as "87DLC", so that vendors selling 486DLC motherboards and systems could include one without revealing that the architecture was 386-based.

CyrixCX87DLC-33QP.jpg
 
IIRC the 486sx could use a 387 FPU technically, I'm not sure anyone ever implemented that configuration. Of course the 487 was actually a 486dx anyway.
 
I have both, the Cyrix Cx486DLC (Cx486DLC-40GP) which is marked "FOR OEM USE ONLY", and is mated with the Cyrix "Fasmath" Cx86D87-GP FPU. Note that there is no "t' after the "Fas".
 
I also have the Cyrix 486DLC-40 with its corresponding FasMath 40 MHz co-processor.
I have to check again but, on my DLC compatible 386 motherboards, there is no option to run the CPU & FPU asynchronously (i.e., at different clock speeds). The FPU will run at the same clock speed as the CPU. If you do get a 40 MHz FPU, then it's fine to run it at a lower clock speed.

Just also want to mention that, apart from maybe two DOS based games from that era that could run satisfactory on this CPU and utilised an FPU (being SimCity & Falcon 3.0) there is no real benefit of adding an FPU.
Essentially a 486DLC without its FPU is similar to a 486SX.

Also make sure your motherboard BIOS supports the 486DLC CPU. Otherwise, you'll have to make use of the cache enabling software to enable the 1 KB of level 1 cache on the CPU.
 
AutoCAD.

I never knew there were games that used FPU back then. But there was plenty of CAD and structured drawing software that did. Most notably, AutoCAD won't even run without it.
 
Hmm, read through that but didn't find exactly what differences there are when it comes to comparing same speed chips from different manufacturers. It looks like they all do the same thing, so it shouldn't matter which brand I end up with?
 
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