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Can UMC U5 processors use a 387DX?

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First post, by demiurge

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So I am kinda stuck on using a UMC U5 to represent the socket 3 era in my collection--but they don't have math co-processors.

Can the UMC U5 use a co-processor if it was in the 387 socket? It looks like a Cyrix 487S doesn't work with the UMC but that chip was notoriously buggy anyway.

Most motherboards didn't have UMC U5 explicitly supported but I figure the U5 could use the settings of a 486SX or 486DLC to work. I don't think they would have been sold if they could only work in the boards with settings specifically for them.

I want a VLB motherboard for the performance. Would the U5 work in boards like:

Reply 3 of 4, by Deunan

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demiurge wrote on 2024-05-04, 14:06:

The U5S had an embedded FPU.

It did not. There were U5D and U5DX2 chips but rare as hen's teeth - I've only ever seen photos of these and always wondered if these were genuine or fake. Not sure if anyone on Vogons have a working system based on U5D?

Cyrix DLC/SLC type CPUs (and also the TI clones), plus their 486S variant which is sort of a hybrid between DLC and "true" 486 as far as bus protocol is concerned, can use external NPU because these were designed for it. It's actually pretty slow because on real DX chip the FPU can pull data from L1 cache (along with the opcodes from the decoder). This alone shaves a dozen clock cycles of each instruction, and there are also other improvements on top of that (like the FPU being able to command the integer ALU to speed up some operations).

Reply 4 of 4, by demiurge

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Yeah I meant U5D not U5S. Well I was going to buy a board that could do the NPU just to see but I guess you saved me 250$. I will instead buy a board with 1 MB cache for my UMC.

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