Gahhhrrrlic wrote on 2026-04-01, 05:40:

I just bought the IIT FPU from group 4 above (because it's supposedly the fastest and only has some fails in sine/cos). But I just want to confirm so I don't blow up my precious machine... These XC87-DLC chips work in a 386 computer??? I thought that was kind of the thrust of the original post but never saw it explicitly made clear whether these chips were being tested on a 386 or 486. Are all of the chips compatible as 387 coprocessors or do some have to be used with 486 sx or something like that? Thanks.

Yes they are all for use with 386 CPUs. It's just branding to make them appear particularly suitable for the 386+ CPUs that appeared later for the 386 PGA132 socket. Like the 486DLC, 486Drx2, 486SXL etc.

Proper 486 CPUs (i.e. using PGA168+ socket) do not support external coprocessors.

Thanks. I'm excited to get mine to replace my ULSI. I think this A type IIT should be much faster. I think IIT had pretty good mul performance. Can't find any documentation on the architecture or instruction latency of the ULSI though to compare...

The latest versions of the ULSI FPU are very fast – just like the CYRIX FPU. The IIT with a v4 core is slower than the ULSI. But the early ULSI is slow.
Notice that the IIT FPU from the v4 and v5 groups always has the inscription 1002FA.
1002FB and 1002FC can be from the v2 or v3 group.

IIT XC87DLC from the v3 group with the inscription 1002FB.