1. No idea, depends on the speed rating of the motherboard components

2. Depends on how it’s controlled but the 16 bit slots are likely synchronized to the cpu

3. Not likely but it may be unstable or corrupt HD data if things are too fast

4. There are only 2 common types, get an assortment of speeds

Hopefully your system came in many speeds so you have a better chance of success

Thanks. What are the two common types of oscilliators out there for these kind of boards? Also, my system didn't come in higher speeds, but others of the same chipset did.

http://www.uncreativelabs.de/th99/m/A-B/31173.htm

Looks like the jumpers on this board don't do much of anything useful. Even though it's fairly modern, it seems to be designed for 8MHz, so if you just toss in a new oscillator things will be thrown off. I'd say your best bet is to overclock to 10MHz, and then toss in a 386 or 486SLC upgrade.

I

386 and 486 upgrade is out of my reach. I don't want to upgrade this system to a 32-bit processor because I have a 386 DX 40 board for that. Also, my board is an AST 202286-002 board if that helps out anyone. There's a 20 MHZ Harris for sale on EBay. Maybe I should get that and try oscilliators from 10,12,16,20 MHZ with it?

You can get the 20MHz CPU, but I think it's unrealistic to go from 8 to 20MHz without changing any timings. Maybe if you can track down the datasheet for your chipset, you might get lucky and find ways of changing ISA clock dividers and wait states.

Yeah, I don't think i'd be able to get to 20 MHZ either, but it's worth trying the oscillators up to 20 MHZ. I think i'd be able to get the 286-20 running at 10-12 MHZ on this board, but 16 and 20 MHZ might be not possible. Dosen't the Harris processor run a lot cooler and use less power than the AMD 286-6/8 I have in my system now?

Not sure what you have now, but the Harris likely does run cooler. It's CMOS. Your 286-8 is probably NMOS.

My board has a 14.31818 MHZ oscilliator on it next to the CPU's oscilliator. Dosen't that keep the ISA bus at a fixed 7.15 MHZ or is that for something else? No clue how ISA clock speeds are derived, sorry.

why not start with a faster ISA vga?
OK 8mhz 286 is not a speed king but that paradise vga is one of the oldest ones... maybe you can get a nice boost replacing it with a cirus or wd one

How much of a speed boost would faster VGA give me?

I have collected 286/8 scene-stuff. should be runable on et4000(sb).
Lot's of cool stuff.

You may have better luck than would first be believed

Given everything but the video is “onboard” there is a small possibility you might be golden to 15-18mhz

And there are 3 “factory set” do not touch jumpers that may affect wait state , ISA timing Or possibly clear the cmos/be for flashing
I don’t think there is any permanent harm in trying
(Just make sure your rom bios, hard drive is backed up and disposable)

Step 1 make sure your ram is 70ns or better
Step 2 see if there is a bios utility that can set a wait state
Step 3 get one of the known overclock friendly VGA cards (I had an old Trident that tolerated 18mhz)
Step 4 if it becomes an issue use an 80pin ide cable with a more modern hard drive

Although a little different I was able to get a Micronics 486 ISA motherboard running a stable 15mhz ISA Bus including ide, vga but the sound was hit or miss
At 18mhz FSB the vga still worked but the HD could be flakey (swapped the 400mb Connor for a 540mb fireball and I could run video in Windows 95), modem was also flakey.

Lastly the classic 4.77mhz oscillator is likely only for date and time, very rarely it would affect the 8 bit ISA bus clock but not likely since 8.33mhz is the normal ISA bus speed that just so happens is also the cpu speed. Occasionally it was used for the “turbo” setting which is also unlikely

Good Luck.

I did try those factory configured jumpers a while ago to change parity settings - sadly, none of those jumpers did that. None of the jumpers cleared the CMOS. 2 of them did nothing noticeable and system booted as normal, the 3rd one just made the VGA card display a white screen and not boot. Maybe those 2 other jumpers control the ISA and wait states, i'll have to check.

There are no magical jumpers on this board. What chipset does the board use? G2?

https://www.datasheetarchive.com/pdf/download … pe=M&term=GC102

What do you mean by "magical jumpers"? Also yes, the chipset is a GC102 chipset.

Old PC Hunter wrote:

What do you mean by "magical jumpers"? Also yes, the chipset is a GC102 chipset.

There are no jumpers on your board that will do what you want them to do (ISA clock dividers).

I had a look at the G2 manual, and I didn't see any functions to divide the ISA clock. So perhaps in this system the ISA always runs at the same speed as the CPU no matter what. I guess it wasn't totally unheard of in the 286 era for this to be the case. Anyway, your chipset seems to be good for up to 16MHz.

*edit* It's also possible that the ISA bus runs at half CPU clock by default, but there was nothing in the manual to indicate that was the case.

Anonymous Coward wrote:

*edit* It's also possible that the ISA bus runs at half CPU clock by default, but there was nothing in the manual to indicate that was the case.

Oh ha. On a 286-8, the i/o speed must be damn slow then, considering that the 286 front-side bus used to resemble the physical part of ISA (or AT-Bus, more precisely).
Hopefully, the G2 chipset can run the CPU at something more pratical, say 10 or 12 Mhz then, without itself getting overheated..

One of my Schneider Tower-AT's does in fact run at 12,5/12,5 and this machine
is blazingly fast...much faster then the Tower386 16Mhz SX.

dr.zeissler wrote:

One of my Schneider Tower-AT's does in fact run at 12,5/12,5 and this machine
is blazingly fast...much faster then the Tower386 16Mhz SX.

Didn't the Schneider Tower-AT run a GC102 chipset too?