Trying to get a 200MHz am5x86 systems going?

Well besides any grand plans like this... 😀 Rather it is (or could be?) a nice adding up to the number of good "flexible" boards...
Good for lesser, but still glorious tasks.

Ah, too bad that they don't exist as it seems 😵

I've changed the topic to include 2/3 and 1/2 multipliers. Has anyone seen a 2/3 or 1/2 PCI multiplier in the BIOS on SiS motherboards, or know of an auto multiplier being added for FSB's higher than 33 MHz?

Look into the Mtech R418 I mentioned. I seem to remember people saying this board had that capability, though I did not see it in the manual.

CONFIRMED support for 1/2 multiplier:

JP25 -- PCI bus clock speed --
1-2 => PCI bus clock = system clock (set by JP 38, 39, and 40)
2-3 => PCI bus clock = 1/2 system clock
(This was confirmed by Ming at M-Tech for "Lionel Hutz, Esq.")
My own experience is that for clock speeds over 40MHz, you
need to use the PCI bus clock divide-by-two setting or your
system won't boot -- I think current PCI specs limit the bus
to 41.5MHz, or something like that.

After years of sitting on the sidelines, I finally found a PCI 486 board that I believe will satisfy my needs...the R418 I mentioned in my last post.

http://www.ebay.com/itm/170984035614?ru=http% … 5614%26_rdc%3D1

Which one of you guys was the other bidder?

I have been regretting not buying one of these since 1997 when I opted for a lemon R534 and K6-200 CPU. The R418 was pretty well loved, and provided a great upgrade path for people still using 30 pin SIMMs. Not only does this board have a 1/2 PCI divider, it also allows for up to 1MB cache and 256mb RAM. The one I just bought has a 1996 SiS 496/497 chipset, so should support the Cyrix 5x86 chips well. I believe this board should be a good candidate for 2x66.
The only real downside I know of at the moment is lack of PS/2 mouse port.

I look forward to the (eventual) test results. For 256 MB on this board, are you allowed to fill the 30- and 72-pin SIMMs simultaneously? I wonder if you'll run into any issues because of this, esp. at 66 MHz.

Normally the 30-pin and 72-pin SIMMs can be mixed as long as you are not mixing FPM and EDO, and everything is rated to the right speed. I have no idea what will happen at 66MHz. I'll probably start with a single 64MB FPM 72-pin SIMM and take it from there. Knowing 486 PCI boards, I am confident things will not go smoothly. If I can get everything sitting nicely with 256MB of RAM, 1MB L2 and a 33MHz clock I'd be happy.

This board supports 3.75V and 3.9V CPUs. You said 3.85V was the sweet spot for 5x86C at 2x66. Will 3.9V cut the mustard?

Those are very unique CPU voltage settings for a 486 motherboard.

Somewhere in the 3.7 - 3.9 V range is the sweet spoot for an IBM 5xc86C-100HF at 133 Mhz. Factors which affect the range are the CPU itself, CPU cooling, case cooling, and which Cyrix 5x86 special features are enabled. You will have a real good time fine tuning all these parameters. A crash may not happen for an hour or more, at which point you need to adjust a parameter and try again. In most cases, if you are testing the board in the open with plenty of cooling, the adjustment parameter will be the voltage or Cyrix feature. From my experience, the -100HF overclocks better than the -100GF, but I have a small sample (two -100HF and two -100GF). The "H" is only supposed to mean it has a factory heatsink...

Actually, if you remove the heatsink from the 5x86C, you will find it also says "GF" underneath. They should all be the same.

I have never removed the heatsinks, but perhaps IBM's adhesive thermal pads provide better heat transfer than the heatsink compound I used.

I own an A-Trend ATC-1425B board, it does have a "synchronous-asynchronous" setting on JP10 position, it is quite possible that it sets PCI bus it to half the systems bus, but i can't be sure. I really want a board with PS/2 mouse, but i also wanted to get an AMD X5 @ 200MHz.

ATC1425B - No PS/2 port, but with PCI bus divider would make 4x50Mhz setting possible by clocking PCI bus @ 25MHz.

Zida 4DPS - PS/2 port, great board, but it has no freakin' PCI divider! And as far as i know there isn't a revision that does. At least 2.1 and 3.1 don't.

I'll probably use the Zida @ 4x40MHz but will need to check all my PCI graphic cards for stability @ 40MHz.

BTW, i think the Lucky Star LS486E also does have PCI bus divider. Need to check all revisions though.

EDIT:

I just realized the OP was mentioning BIOS and not a normal jumper.

Aside from the 4DPS not having a PCI divider (well, it may have, but you'll need to figure out how to hack it), is that even if you plan to run it at 40x4, there is some limit whereby the memory read will need to be lowered to that of 33 MHz to gain stability. Refer to this thread, Help with SiS 496/497 Tomato 4DPS 486 motherboard

The need for a PCI 486 board with PS/2 may be reduced if you find this converter works well,
PS/2 to Serial Mouse protocol converter

carlostex wrote:

I just realized the OP was mentioning BIOS and not a normal jumper.

BIOS or jumper, doesn't matter, as long as it has the option somewhere.