VOGONS


First post, by appiah4

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On a whim I bought and restored a mystery Baby AT 386 motherboard a while back; I was hoping it was a DX40 - Nay, I was CERTAIN it was a DX-40 because I could read the "40" bit on the CPU (the rest was covered in dirt) but when it arrived and I cleaned it, it turned out to be an SX40:

Unknown-OPTi-82-C291.jpg

So I guess the question is, considering this is the slowest CPU and motherboard I own, and the next step up build I have is a 486, does this board serve any purpose? Would it be fun to build around this and pretend it's basically a 286?

And ultimately, why? Why did such things as a 386 SX-40 exist? Was there demand for such high clockspeed bandwidth starved crippled CPUs at the time? Maybe for business purposes?

Last edited by appiah4 on 2019-05-02, 12:35. Edited 1 time in total.

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 1 of 50, by Deunan

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Nice, an SX with cache. Can you run "CACHECHK.EXE -x5 -z >RESULT.TXT" on it and post the output file?
It should score somewhere around DX-33, but that depends on how good/bad the cache misses are and OPTi is not exactly known for their superior memory performance. Still, it's a nice, compact mobo, and way cheaper to manufacture than a DX-33 too (half the data bus width, less address lines).

Last edited by Deunan on 2019-05-02, 12:36. Edited 1 time in total.

Reply 2 of 50, by Scali

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The performance difference between a 386SX and 386DX is not all that big in practice (the ISA bus is only 16-bit anyway, and is a big bottleneck for the DX).
The biggest difference is that most SX motherboards don't have cache, while many DX boards do. However, it looks like your board has some cache chips on there.
So it may be quite a high-end 386SX board (which would make sense, given the 40 MHz CPU).

The 386SX existed because it was a way to reduce costs: the 16-bit bus meant that you could basically recycle cheap 286 chipsets. A 386SX-40 gave you pretty impressive bang-for-the-buck.

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Reply 3 of 50, by appiah4

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The ISA BUS is a limiting factor all the way up to VLB but 16-bit memory access should really cripple this bard, no? The cache really helps that much? If it can indeed do speeds of around DX-33 I would be greatly impressed.

Time to make a build around it I suppose. What would be a good period to target with this board/CPU? A fast 286 stand-in for 1987-1989 sounds fair? I suppose it could play stuff from up till 1991 or so? I do remember my friend's 386 really struggling with games like Civilization and Dune II whereas my 486 DX33 could breeze through it; can't remember if it was a DX or SX though..

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 4 of 50, by BinaryDemon

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The 386 SX-40 is probably too close In performance to your 486 that there would be little reason to choose it, I doubt many people at the time upgraded from 386 sx-40’s to a 486 sx-33 (expensive). Still it’s any interesting piece of hardware.

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Reply 5 of 50, by appiah4

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BinaryDemon wrote:

The 386 SX-40 is probably too close In performance to your 486 that there would be little reason to choose it, I doubt many people at the time upgraded from 386 sx-40’s to a 486 sx-33 (expensive). Still it’s any interesting piece of hardware.

I can always repurpose my 486 as a DX40, DX2-50 or DX2-66 to better differentiate the two.. The DX2-66 sounds like a good midpoint between the 386 SX-40 and Pentium 133, no?

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 6 of 50, by matze79

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I have a 386SX33 without Cache and its comparable to a DX25 at least.

The SX40 was long time manufactured, for Industrial Systems, Control Systems, Machines etc.

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Reply 7 of 50, by GrooBR

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I find this topic and I have this same board, but it is incomplete. It does not have the CPU, the BIOS, cache chips and coprocessor socket.
https://postimg.cc/grGdWLmr
I'll buy a 386sx40 processor from china and want a copy of BIOS. I'll try to find it on some repository site, but some pictures from the power on screen will help me so much. May you post any ?
Cache chips, memory everything else I have here.
Sorry for any language error, I'm doing my best .
Thanks so much !

Reply 8 of 50, by appiah4

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GrooBR wrote:
I find this topic and I have this same board, but it is incomplete. It does not have the CPU, the BIOS, cache chips and coproces […]
Show full quote

I find this topic and I have this same board, but it is incomplete. It does not have the CPU, the BIOS, cache chips and coprocessor socket.
https://postimg.cc/grGdWLmr
I'll buy a 386sx40 processor from china and want a copy of BIOS. I'll try to find it on some repository site, but some pictures from the power on screen will help me so much. May you post any ?
Cache chips, memory everything else I have here.
Sorry for any language error, I'm doing my best .
Thanks so much !

Here's a video of the boot process: https://youtu.be/cebsE0l83M4

My board is somehow damaged though despite my attempts at repairing it POST hangs after initial tests with a keyboard error, probably the controller needs replacing.

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 9 of 50, by Deksor

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The 386SX don't always need cache because some 386SX let you use the ram at the maximum speed the bus can handle thus no need for cache.

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Reply 10 of 50, by keropi

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nice , a 386sx with cache these are always nice boards! looks like it will support 64kb of cache so it will cover the 16MB of ram the system supports.

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Reply 11 of 50, by appiah4

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keropi wrote:

nice , a 386sx with cache these are always nice boards! looks like it will support 64kb of cache so it will cover the 16MB of ram the system supports.

Mine doesn't POST though and despite extensive efforts I couldn't fix it: 386SX-40 Motherboard Not POSTing

Any help would be appreciated at this point, I'm even OK with covering shipping to and from someone who wants to have a hand at repairint it for me as a project.

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 12 of 50, by Scali

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Deksor wrote:

The 386SX don't always need cache because some 386SX let you use the ram at the maximum speed the bus can handle thus no need for cache.

That would only go for the slower SX models though, I suppose? Like the 16 MHz one, possibly 20 MHz.
At 40 MHz there wasn't any memory fast enough, I'm sure.

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Reply 13 of 50, by Deksor

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Yeah I believe so. Mine is a SX25. 70NS sticks are good enough for that use.

But for some reasons 386DX never let you do that, making the ram bus speed much slower, so much that it makes a cacheless 386DX not much faster than a 386SX with full bus speed.

Trying to identify old hardware ? Visit The retro web - Project's thread The Retro Web project - a stason.org/TH99 alternative

Reply 14 of 50, by Scali

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Yea, I think what also matters is that a 386 is basically stuck in-between 16-bit and 32-bit software.
That is, it can technically run 32-bit software, but it's barely fast enough for an early 32-bit game like DOOM. A full 32-bit OS like Windows NT or linux is overkill.
So in practice you probably mostly run 16-bit games and other software on it. And in that case, all memory access is 16-bit anyway, so the 386DX doesn't get much of an advantage at all.
And even in 32-bit games, especially the early ones that would actually run okay on a 386, generally a lot of time is spent updating the video memory, which is still a 16-bit bus, so again no advantage for the DX. It only has an advantage on accesses to system memory.

http://scalibq.wordpress.com/just-keeping-it- … ro-programming/

Reply 15 of 50, by keropi

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appiah4 wrote:

Any help would be appreciated at this point, I'm even OK with covering shipping to and from someone who wants to have a hand at repairint it for me as a project.

I would re-check the keyboard traces and made sure they are OK
also try to connect a battery and see if that helps... but my money is on the keyboard and nearby traces - something is broken there and causes this slow boot

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Reply 16 of 50, by appiah4

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Scali wrote:
Yea, I think what also matters is that a 386 is basically stuck in-between 16-bit and 32-bit software. That is, it can technical […]
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Yea, I think what also matters is that a 386 is basically stuck in-between 16-bit and 32-bit software.
That is, it can technically run 32-bit software, but it's barely fast enough for an early 32-bit game like DOOM. A full 32-bit OS like Windows NT or linux is overkill.
So in practice you probably mostly run 16-bit games and other software on it. And in that case, all memory access is 16-bit anyway, so the 386DX doesn't get much of an advantage at all.
And even in 32-bit games, especially the early ones that would actually run okay on a 386, generally a lot of time is spent updating the video memory, which is still a 16-bit bus, so again no advantage for the DX. It only has an advantage on accesses to system memory.

This is all fine until you try to run Windows 3.x on a 386SX though; in my experience the DX runs circles around the SX when in 386 Enhanced mode, expecially for Windows 3.1

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 17 of 50, by appiah4

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keropi wrote:
appiah4 wrote:

Any help would be appreciated at this point, I'm even OK with covering shipping to and from someone who wants to have a hand at repairint it for me as a project.

I would re-check the keyboard traces and made sure they are OK
also try to connect a battery and see if that helps... but my money is on the keyboard and nearby traces - something is broken there and causes this slow boot

I have checked them again and again, but I will try one more time tonight. This board has me tearing out my hair, I desperately want to get it to work so I can replace the SX-25 in my 386SX build with it.. It would be SO much faster.

Retronautics: A digital gallery of my retro computers, hardware and projects.

Reply 18 of 50, by Scali

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appiah4 wrote:

This is all fine until you try to run Windows 3.x on a 386SX though; in my experience the DX runs circles around the SX when in 386 Enhanced mode, expecially for Windows 3.1

Yea, but then you're running 32-bit code.

http://scalibq.wordpress.com/just-keeping-it- … ro-programming/

Reply 19 of 50, by Grzyb

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appiah4 wrote:

And ultimately, why? Why did such things as a 386 SX-40 exist? Was there demand for such high clockspeed bandwidth starved crippled CPUs at the time? Maybe for business purposes?

Sure, 386SX machines were mad popular in the era.
They were considered "386 for the price of 286" - this also explains why 20 and 25 MHz 286s are so uncommon: 386SX was only a little more expensive, and offered much greater capabilities.
Sure, SX is somewhat slower than "the real 386" (DX), and too slow for true 32-bit stuff: OS/2 2.0+, Windows NT, Doom...
But it's enough to run EMM386, Windows 3.x in 386 enhanced mode, and all the real-mode software that occasionally uses 386 instructions - and that's all what was needed for an average user until at least 1995.

Żywotwór planetarny, jego gnijące błoto, jest świtem egzystencji, fazą wstępną, i wyłoni się z krwawych ciastomózgowych miedź miłująca...