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Choosing 386 motherboard and CPU

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First post, by lalakobe

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Hi guys!

I'd like to build 386 machine from scratch, can you advise me, what motherboard should I be searching for?

I've had 386SX back in the days (1993-1997 I think), now I want something more powerful 😀

I want to install fastest Intel 386DX (is it 33 mhz? A80386DX-33?) and Intel FPU (also 33 mhz? A80387DX-33?)

Were there any 386 motherboards with CR-2032 battery?

Any advice is much appreciated!

Reply 2 of 28, by debs3759

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Anders- wrote on 2022-01-25, 21:15:
lalakobe wrote on 2022-01-25, 21:02:
Hi guys! […]
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Hi guys!

I'd like to build 386 machine from scratch, can you advise me, what motherboard should I be searching for?

I've had 386SX back in the days (1993-1997 I think), now I want something more powerful 😀

I want to install fastest Intel 386DX (is it 33 mhz? A80386DX-33?) and Intel FPU (also 33 mhz? A80387DX-33?)

Were there any 386 motherboards with CR-2032 battery?

Any advice is much appreciated!

If you can somehow get a 33MHz intel rapidcad to work together with a fasmath you might get nice performance with 2 fpu's, I guess the "dummy" in the 387 socket has a role to play though...

Not possible. The Rapidcad-1 in the CPU socket needs the Rapidcad-2 in the FPU socket, leaving nowhere for a 2nd FPU to go.

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Reply 3 of 28, by stamasd

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The fastest "386" CPU that runs on a regular 386 motherboard is probably this: https://www.cpu-world.com/CPUs/80386/Cyrix-Cx … x2-25-50GP.html It's actually a 486-class CPU but compatible with the 386 bus. It's also clock-doubled so it runs at 50 MHz internally on a 25MHz bus (which is fairly standard for 386 machines).

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Reply 5 of 28, by Matth79

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The fastest "real" 386 is AMD's 386DX40, on a board which has cache and an IIT 4C87DLC-40 FPU for the FPU
You could go higher with some 386->486 type hybrids, but if that's the speed target, a 486 would be a better choice to begin with

Reply 8 of 28, by Horun

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There are two variants of the FasMath one is about same as IIT in Transform Mflops, LLL Mflops, Linepak Mflops, and Whetstone, the other (Cyrix EMC87 based ) is only about 10% more according to a website that ran 6 diff tests on each Math-co.
I agree with Matth79 in "The fastest "real" 386 is AMD's 386DX40, on a board which has cache and an IIT 4C87DLC-40 FPU for the FPU".
Being a 386 you really only need 64k cache because it would be stupid to run more than 16mb ram on a 386... just my opinion 😀

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor.

Reply 10 of 28, by debs3759

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Anders- wrote on 2022-01-25, 23:41:

I reckon the next thing to debate is whether to get a vlb board or not 😁

VLB is always good, if you can find and afford a 386 board with it 😀

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Constantly being worked on. Feel free to message me with any corrections or details of cards you would like me to research and add.

Reply 11 of 28, by Horun

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debs3759 wrote on 2022-01-26, 00:05:
Anders- wrote on 2022-01-25, 23:41:

I reckon the next thing to debate is whether to get a vlb board or not 😁

VLB is always good, if you can find and afford a 386 board with it 😀

Agree ! 😀

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor.

Reply 12 of 28, by Deunan

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My own tests show Cyrix CX-83D87-40-GP FASMATH to be quite a bit faster (in some tests close to 2x) than ITT 4C87DLC-40, both with 386DX-40 and 486DLC-33. The code used mostly FMUL, FADD, FCOM as well as FSIN/FCOS/FSINCOS (in 287-mode) and F2XM1, and very little FDIV. Also no advanced functions of IIT were used (like extra register banks or matrix ops). Frankly the IIT chip barely beats Intel A80387DX-33 (this is the improved one), and even looses slightly in some benchmarks.

I'm surprised any decent benchmarks would show Cyrix as equal to IIT, or even slower. Could be another case of "bugs" like in Norton SysInfo that show Cyrix CPUs with much lower performance index than Intel ones?

Reply 13 of 28, by GigAHerZ

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For my 2 cents here in this topic, i would recommend a motherboard not only with cache, but with a cache that is capable of writeback.
One of such boards is M-321: https://www.ultimateretro.net/en/motherboards/3059

On top, you may want to closely check the chipset registers to tighten some settings more than the bios allows. For M-321, MR-BIOS is also available, that doesn't need any "out-of-bios" tuning in my experience. 😉

"640K ought to be enough for anybody." - And i intend to get every last bit out of it even after loading every damn driver!

Reply 14 of 28, by konc

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Ah yes the classic, someone asks which car is good as a daily drive and people start discussing whether a Ferrari is better than a Lambo while also suggesting a rare 10 units prototype 😀
You have already chosen the cpu so just get whatever you can find in good condition that has it, make sure it has cache although DXs usually had.

Reply 15 of 28, by bloodem

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Deunan wrote on 2022-01-26, 12:32:

My own tests show Cyrix CX-83D87-40-GP FASMATH to be quite a bit faster (in some tests close to 2x) than ITT 4C87DLC-40, both with 386DX-40 and 486DLC-33. The code used mostly FMUL, FADD, FCOM as well as FSIN/FCOS/FSINCOS (in 287-mode) and F2XM1, and very little FDIV. Also no advanced functions of IIT were used (like extra register banks or matrix ops). Frankly the IIT chip barely beats Intel A80387DX-33 (this is the improved one), and even looses slightly in some benchmarks.

I'm surprised any decent benchmarks would show Cyrix as equal to IIT, or even slower. Could be another case of "bugs" like in Norton SysInfo that show Cyrix CPUs with much lower performance index than Intel ones?

The IIT FPU in aluminum package hands down beats EVERYTHING, because it just looks awesome. 😁

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Reply 17 of 28, by bloodem

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Anders- wrote on 2022-01-26, 18:11:

What about the weitek then? It's much larger than the others and won't fit in the regular fpu socket? 😁

That one is nice but for different reasons (because it's rare), however, when it comes to the way it looks... I find it quite average with its ceramic/golden package. 😀

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Reply 18 of 28, by Deunan

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Weitek is technically the fastest NPU for a 386 (we can argue if RapidCAD is actually a "386"), but only in the same sense as F1 is the fastest "car". Since I can already tell OP will not be using it in any fashion, why no go for looks and rarity, sure.

EDIT: Beware though, Weitek being a completly different thing does require a special socket and mobo support. In case this wasn't clear.

Reply 19 of 28, by dionb

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Tbh, OP, given the rarity of 386 boards, and the fact that most of what is left is 386SX, I'd sooner focus on what is available to you within acceptable distance and budget, and then choose from the options you have available.

If you are lucky enough to have multiple options, a lot depends on what you want to do with the system exactly. Do you prefer to constantly mess around with hardware, or do you prefer to build once, close the case and then only get involved with the software?

If you like messing around with hardware - like most of the people responding here, me included - you should probably look to the most versatile board you can find. I'd suggest a 386/486 board, which gets you very high performance, cache, VLB and the option to run both classic 386 CPUs and 486 but more interestingly most of the DLC souped-up 386 CPUs. Look for something like the Auva CAM 33-P9, or more generically anything with the OPTi-495SX chipset which was invariably used for those boards.

However given your topicstart I suspect you're not that interested in constant tweaking. In that case, a 'classic' 386 board with regular 387 co-pro socket is probably best and will definitely look 'cleaner' than one of those late jack-of-all-trades. The first Asus boards (ISA-386xxx) are generally considered excellent, but again, chance of finding something specific is minimal, so just look at what you can get and choose there.

Last edited by dionb on 2022-01-28, 22:56. Edited 1 time in total.