VOGONS


First post, by SSTV2

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Has anyone successfully overclocked a AMD 486DX4 100 or 120MHz to 150MHz? I couldn't find any reliable proof of it on the net, only this thread: My 486 (150MHz and Voodoo!). I think that Speedsys is misreporting am5x86 CPU there (this CPU was mentioned in youtube video below).

I've tried to OC two am486DX4-100 CPUs, both did work @ 120MHz (3x40) and @ 100MHz (2x50), but @ 150MHz, system wouldn't POST, even when core voltage was raised to 5V. It seems that my plan of having a 150MHz DX4 CPU in a GA-486VM motherboard - failed.

Reply 1 of 17, by LunarG

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I've read about people running the AMD 5x86-133 at 160 (presumably 4x40) reliably, but I've never tried it myself. I don't really feel like I want to risk such old hardware by overclocking it. If I need something faster, I'll build a Pentium system.

WinXP : PIII 1.4GHz, 512MB RAM, 73GB SCSI HDD, Matrox Parhelia, SB Audigy 2.
Win98se : K6-3+ 500MHz, 256MB RAM, 80GB HDD, Matrox Millennium G400 MAX, Voodoo 2, Waveforce 192XG.
DOS6.22 : Intel DX4, 64MB RAM, 1.6GB HDD, ELSA Winner 1000PRO, GUS 1MB, SB16.

Reply 2 of 17, by jesolo

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You can safely overclock and AMD 5x86 to run at a FSB of 40 MHz (4 x 40 Mhz = 160 MHz). It's been tested by various users and it's stable at that speed. It's probably one of the few CPU's that easily overclocks to 160 MHz and the performance gain is quite impressive - refer The Ultimate 486 Benchmark Comparison.
It's when you go above that speed that things start to get tricky.

On the other hand, I completely understand your point.
Back in the day, when CPU's and motherboards were expensive to upgrade, and you wanted to squeeze a bit more out of your current hardware, it made sense to overclock.

Reply 3 of 17, by LunarG

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I am happy to overclock modern stuff. It is replaceable. My daily driver, an i7 6700k, runs at 4.5GHz (conservative overclock) on custom watercooling loop. If anything fails, it is possible to get new parts over the counter. If a motherboard or cpu or other piece of hardware from 199x fails, it is lost. There are no new ones being manufactured. That's why I don't really like overclocking it. That being said, I do overclock my K6-3+, but as it is technically a laptop/low power cpu, it still runs lower voltage than the normal desktop version, and it has better than stock cooling.
I guess that kind of makes me a hypocrite. I just tend to value old hardware more than new, because it the fact that it isn't easily replaceable.

WinXP : PIII 1.4GHz, 512MB RAM, 73GB SCSI HDD, Matrox Parhelia, SB Audigy 2.
Win98se : K6-3+ 500MHz, 256MB RAM, 80GB HDD, Matrox Millennium G400 MAX, Voodoo 2, Waveforce 192XG.
DOS6.22 : Intel DX4, 64MB RAM, 1.6GB HDD, ELSA Winner 1000PRO, GUS 1MB, SB16.

Reply 4 of 17, by jesolo

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I totally agree with your viewpoint.
I also don't like to overclock my vintage hardware and, considering that I also have Pentium 1 systems, if I want something faster than a 486 then I'll build the appropriate system.

However, based on some posts I've read, some of the AMD 5x86 CPU's were actually rated to run at 160 MHz (they were just marked to run at 133 MHz for marketing reasons).
My main concern about overlooking to a FSB of 40 MHz is that some other hardware then also runs at a bus speed of 40 MHz, which can then lead to stability issues (particularly on PCI based motherboards).
Personally, I like to run all my 486 systems at a FSB of no more than 33 MHz.

Reply 5 of 17, by Anonymous Coward

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I think overclocking an AMD DX4-120 (.5u) to 150 *might* be possible, but you'd probably have to dig through dozens of chips to find one that worked okay. It would probably be about as easy as overclocking the DX5 to 180.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 6 of 17, by SSTV2

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Anonymous Coward wrote:

you'd probably have to dig through dozens of chips to find one that worked okay

As I expected, you'd have to win silicon lottery, basically. Could somebody give theirs DX4s a try and post a proof of reaching 150MHz?

Reply 7 of 17, by leileilol

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160mhz for an am5x86 isn't too bad, probably the best result for Quake.

I never had a successful 150mhz though. I always had freezes with that, probably because I use PCI and maybe the M919 board's a factor, even though it theoretically should be faster than 160mhz for better PCI clocks, quake didn't run any faster than 160. Again this is an AM5x86 CPU, not the AM486 you've mentioned.

Also note the AM5x86 will identify as an AM486 on x3!!!

apsosig.png

Reply 8 of 17, by The Serpent Rider

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I think it's not reliably possible for 0.5um 486s, especially on any non-Intel lithography, to work without efficient cooling below zero Celcius temperatures. There's also the FSB wall problem.

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Reply 10 of 17, by feipoa

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What I recommend is first determining which motherboard and hardware settings will run properly with an Am5x86-133 ADZ or ADW at 3x50 MHz. Ensure that system is stable. While it is likely that your settings at 2x50 may be suitable for 3x50, they may not. I've witnessed such anomolies whereby increasing CPU speed, but not FSB, have required reduction in SRAM or DRAM wait states, for example.

{I'm currently posting from an Am5x86-160 system w/ IE5.5}

EDIT: The next time I have a 486 system out, I'll try overclocking an AMD DX4 100 or 120 to 150 MHz. Any reason you don't want to use an Am5x86? The later AMD DX2's and DX4's from 1998-2002 should probably work at 150. My DX2 with a 2002 datecode would run at 166 MHz (2x83).

Ultimate 486 Benchmark | Ultimate 686 Benchmark | Cyrix 5x86 Enhancements | 486 Overkill Graphics | Worlds Fastest 486

Reply 11 of 17, by SSTV2

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feipoa wrote:

What I recommend is first determining which motherboard and hardware settings will run properly with an Am5x86-133 ADZ or ADW at 3x50 MHz. Ensure that system is stable.

Done and ensured. System that I used to OC DX4 works rock solid with 5x86 @ 150MHz, it can even do 180MHz at room temp., but it's not too reliable.

feipoa wrote:

{I'm currently posting from an Am5x86-160 system w/ IE5.5}

That's some dedication 😉

feipoa wrote:

Any reason you don't want to use an Am5x86?

I'd love to, but availability and price holds me back. At this moment, I can buy few 0.5um chips locally for cheap, but as far as I can see, chances of making one run @ 150Mhz reliably are far too low.

Now the fun part!

am486DX4-100 (SV8T) running @ 150MHz, 5V core: 😎
t5w3QLYl.jpg

Ambient temperature in the balcony with windows open:
jEkQWSPl.jpg

System with AM486DX4 CPU at this frequency, would post only when CPU would be below 0*C, after minor warming up, system would refuse to post. Could not make it boot from HDD either...

Same system, but with 5x86 @ 200MHz, 5V:
MeZZVDul.jpg

It was even less functional.

Reply 12 of 17, by The Serpent Rider

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Have you tried to reduce the CPU voltage to 4v? It might help to even boot up the OS 😈

Get up, come on get down with the sickness
Open up your hate, and let it flow into me

Reply 14 of 17, by The Serpent Rider

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Then it's settled - it's impossible to run that CPU overclocked under normal conditions (room temperatures).

Get up, come on get down with the sickness
Open up your hate, and let it flow into me

Reply 15 of 17, by amadeus777999

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Sucks,
one of the ADZs I have boots up to 198 but no programms can be run. At 5V it doesn't boot, only up to 4.4V I think.
Does yours run at 180 and if so at how high a voltage?

Reply 16 of 17, by SSTV2

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The Serpent Rider wrote:

Then it's settled - it's impossible to run that CPU overclocked under normal conditions (room temperatures).

For the classic ones - pretty much, but newer embedded 486 CPUs should, like feipoa stated.

amadeus777999 wrote:

Does yours run at 180 and if so at how high a voltage?

Can't remember what voltage I used back then, it was probably 5V. I had it OCed to 180MHz really long time ago, after doing a non-destructive mod to the PLL (for 60MHz FSB support).

Reply 17 of 17, by The Serpent Rider

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but newer embedded 486 CPUs should

They're pretty much identical to AMD 5x86 ADZ with 350nm lithography.

Get up, come on get down with the sickness
Open up your hate, and let it flow into me