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Topic Title: 486-DX overclocking
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Created On: 02/17/2005 12:55 AM
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 02/17/2005 12:55 AM
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Charlie22911
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i have here a 50Mhz 486-DX that im fixing up for my GF and every Mhz i can get counts. if anyone can help me get any overclock of anykind it would realy help. i hear overclocking in 486 Cpus was common and being that im only 16 i hope some of the more experienced users can help.

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 02/17/2005 02:44 AM
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amosf
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Well, about the best bet there for some fun would be to drop another chip into it... Like a DX4-100 or a socket 3 AMD 5x86 p75 - 133... I have two of those in my greasy little hands right now... If the MB can take it, of course... I got heaps of these on ebay, but not much use any more...
 02/17/2005 02:48 AM
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traviss
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You're talking about overclocking a 10 year old CPU...

Quite honestly, any gain you might get will be totally offset by the shortened life. Leave it at stock, it's just not worth it.

Unless you want to kill it, then go ahead
 02/17/2005 03:04 AM
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OliverMaltby
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Mate it wouldn't even be worth it, if you want a PC which can actually run todays apps then go for a 500Mhz+ system for like £100, as anything rated at that speed won't keep up at all.

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 02/17/2005 03:19 AM
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amosf
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Hey, come on, I had linux running on a 3meg ram, 386sx25 the other day and had vi going and everything

(maybe I can get some help overclocking this? Like solder a new crystal in or something???)

I also have a working desktop system on a Pentium clocked at 188mhz with 64meg ram running mandrake 9.2 and KDE quite well with just a few tweaks - but that's getting to the very low end of useable PC's... Even my firewall is a P166MMX these days.

486's are really not much use thee days, esp when I get K6-2-500's for free as people dump them... I even got a thrown away P4 2.4gig CPU, MB and 256 RAM the other day - no lie. Some people have too much money and not too bright...
 02/17/2005 04:44 AM
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Amitola85
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I had a pair of old Compaq 486DX/66 that I overclocked to 100mhz... I think I just found the jumpers on the motherboard for the multiplier and frequency, and just jacked them up to the highest settings.. They were running fine (had win95 playing Diablo, WCII, Total Annhilation.....) and the other one ran Linux....

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 02/17/2005 04:54 AM
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srg86
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My 486 machine uses an Am5x86-P75-S 133MHz running at 160MHz and 64MB RAM. It now says Am5x86-P90-S. It's running on a 40MHz FSB.

BTW This 486 50 you have, is it a DX50 or a DX/2 50. If it's a DX50 then your out of luck as the highest any 486 board will go, and you need a decent board not some PCChips fake cache crap, is 50MHz.

If it's a DX/2 50, then by all means, as that's on a 25MHz FSB.

I would seriousely recommend an Am5x86 if the motherboard can take it. At 133MHz you'll just about get one to play an mp3 in Winamp 2.x on Windows 95 (A 486DX4 100 won't BTW).

What's this machine going to be used for. A 486 running Windows 95 and 32MB RAM should be able to do word processing, e-mail, spread sheets, simple presentations and MS Paint with ease.

Oh yes, and PCI is a MUST! Otherwise even web brousing will be slow. Ok ok so VLB will work but not recommended.

srg
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 02/17/2005 07:05 AM
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Megadeth
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You can run Linux on a Pentium 100. However, to compile/install kernel 2.6.10, it took around 350 minutes.
 02/17/2005 03:39 PM
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eddaweaver
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Charlie, you need to tell us the motherboard model and the specifications you can see (Socket type, bus, L2 cache, RAM type etc). Setting the jumpers on 486 motherboards is usually very tricky, you will probably need a manual.

If it is an actual DX50 (50MHz FSB), then that CPU isn't going to be overclockable. The DX50 is very rare, and if that's what you've got, it's a collector item. It is bad in the sense that you can't overclock it, but if you've got a working 486 computer with a 50MHz FSB, then the plus is that it's going to be very fast if you put a better CPU in there (eg DX4-100MHz / 50MHz FSB x 2). FSB is much more important with 486s than you're acustomed to with newer computers, so a DX50 system isn't 'half' the speed of a typical DX4-100MHz system on 33MHz FSB x 3.

More likely it's a DX2-50MHz on 25MHz FSB. The motherboard should support higher FSB speeds, but it might not. Most 486 motherboards used VESA local bus, but some early are ISA only, and some later are PCI only or PCI with VESA and ISA. Most 486 systems are unusable beyond 33MHz FSB. VESA local bus devices are specified for up to 40MHz FSB, but many bomb out at 40MHz. This is why DX-50MHz systems on 50MHz VLB FSB are exceptional, as it is so rare to be stable at that speed; hdd controllers on VLB often randomly corrupt past 33MHz, video cards sometimes won't work etc.
A few later PCI 486 motherboards actually support 66MHz & 60MHz FSB with a 2/ divider for the PCI. But I doubt you've got a PCI board as either a DX2/50 or DX50 wouldn't be sold on a later 486 system.

Your best bet is to actually replace the CPU. This is where things can be tricky, or easy, depending on the motherboard model and the CPU you want to use. Second hand 486s are mostly very cheap (1$ etc).

If my memory serves me right, standard DX4-100s had their multipliers unlocked, but the DX4 'OverDrive' chips with integrated heatsinks were multiplier locked to 3x.

The OverDrive DX4s and earlier DX4s don't support Write-back caching, which makes them slower. The motherboard bios needs to support the feature for it to work, though.

The OverDrives have got built-in voltage regulation, as not all motherboards supply the correct voltages to run later CPUs.

Early AMD DX4-100s are inferior to Intels; only 8kb L2 cache vs 16kb. The AMD DX4-120 is fine though if it is properly supported. The PR75 / 133MHz Turbochip or whatever you want to call it from AMD is a 133MHz 486 with a locked 4x multiplier. Many people overclocked them to 160MHz by running on 40MHz FSB. But they're rare now. The 133MHz Cyrix is the fastest CPU you can put in a 486 motherboard, but they're so rare you'll never find one, and many motherboards won't take them. The 83MHz Pentium OverDrive is a good chip but only if you've got lots of L2 cache, as otherwise it's no faster than a DX4-100.

This is probably the only modern browser that's going to be practical on a 486:
http://kmeleon.sourceforge.net/' ">http://kmeleon.sourceforge.net/

http://users.erols.com/chare/486.htm' ">http://users.erols.com/chare/486.htm
http://users.erols.com/chare/sockets.htm' ">http://users.erols.com/chare/sockets.htm


This is probably a bit more elaborate than with with Socket 7s
 02/17/2005 04:23 PM
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Charlie22911
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well, im going to crack the case again and look at that stuff, its only got ISA slots and i upgraded to 64Mb ram and running win95SE real snappy. i will be back in about an hour to give the info i find.
thanks a whole bunch BTW.

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 02/17/2005 04:49 PM
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Charlie22911
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ok i got the info, didnt take as long as i thought. i got pics of the chipset cpu and what i believe is the PLL:



it is a 486-DX2 so its overclockable? i can superglue a better heatsink with a fan on her if i need to.

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 02/17/2005 04:50 PM
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MD - Moderator
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Find an overdrive cpu with an AMD cpu in it...

MD

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 02/17/2005 04:56 PM
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Charlie22911
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all it would be used for is internet music-cd's email and mabye IM.
i dont want to buy anything unless i absoulty have to because of the high shipping cots from ebay and the fact that my grandpa dont have the nervs for it (he does all that stuff, wont let me do it )
every thing seems to be silkscreened in a language i dont understand (i only speak english) so i dont know what those many jumpers are.

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 02/17/2005 05:26 PM
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eddaweaver
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The chipset seems to be an early 486 chipset used on some obscure Taiwanese motherboard brands like "TMC". Some of these motherboards are impossible to find the manuals for.

To overclock it, you will need to change the jumpers to increase the FSB to 33MHz... if the motherboard supports 33MHz FSB, that is... but it probably does. Upping the multiplier to 3x on 25MHz FSB would be pointless.

Could you peal back that sticker on the Socket to see whether it's a Socket 3 or not?

http://groups.google.ca/groups...0+66....ucf.edu&rnum=1' ">http://groups.google.ca/groups...asus.cc.ucf.edu&rnum=1

I get the impression it should work at 66MHz so long as there is enough cooling.
 02/17/2005 05:37 PM
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Charlie22911
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yes, its socket3. what kind of overclocks can be done on this cpu?

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Phenom II x6 1055T @ 4GHz | 4x2GB Patriot DDR3 1600 @ 2000 | 3x AMD Radeon HD6970 Crossfire

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 02/17/2005 06:38 PM
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eddaweaver
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Well 33x2/66MHz should work so long as there's enough cooling; it's a 5volt CPU. I don't know whether 80MHz would work, but you could try if you wish, I doubt it'd actually damage the CPU if it didn't work.
If it is an ISA motherboard, there should be facilities in the bios for setting the ISA clock to something appropriate for various FSB speeds.

But anywhichway, you'll need to figure out how to set the FSB jumpers to do anything.
 02/17/2005 06:40 PM
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Charlie22911
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ugg, i tried fiddling with every jumper on the entire board and still saw only 50Mhz on the post screen (when i got one). if it cant be overclocked what is the best cpu a socket3 board like this can take?

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Phenom II x6 1055T @ 4GHz | 4x2GB Patriot DDR3 1600 @ 2000 | 3x AMD Radeon HD6970 Crossfire

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 02/17/2005 06:57 PM
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eddaweaver
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it should take the i486DX4ODPR-100 chip as listed on C.Hare's site (DX4-100 OverDrive with locked multipliers and voltage converter).

But for it you be worthwhile, you'd need to figure out how to set the FSB to 33MHz.

http://search.ebay.com/overdri...ters...ntrypageZsearch' ">http://search.ebay.com/overdri...Z1QQcoentrypageZsearch

I assume a Socket 3 motherboard would support lowering the vcore to 3.3v, but again you must know the jumpers. The other upgrade possibilities may burn up on 5v, like how an Athlon XP would on 3.3v. Bios upgrades tend to be needed too for the Cyrix 5x86, AMD 5x86 133MHz, Pentium OverDrive etc, which would need the motherboard to be identified at the least. Also, early 486 motherboards are like to have an EEPROM bios rather than a flash bios, which require an EEPROM burner device. I wonder if the bios string would give any clues.

The the motherboard is certain to support FSB speeds other than 25MHz, with some jumper config... you should at least see it booting at 40MHz from some combination.

Is there nothing on the motherboard that could identify the brand or model?
 02/17/2005 07:41 PM
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eddaweaver
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Hm I forgot the DX4 has got 16kb of cache vs 8kb on earlier 486s...

The DX4 @ 75MHz (25x3) is slightly slower than a DX2 @ 66MHz (33x2).

Perhaps there'd be a computer flea market near where you live where you could pick up a DX4OD for a dollar.
 02/17/2005 07:51 PM
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KachiWachi
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What is everyone's thought on an 83MHz P24-T?

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