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Thread: IBM 5x86 in a 486 system with PCI slots?

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    Default IBM 5x86 in a 486 system with PCI slots?

    I have a 486 system with PCI slots and an Intel i420 chipset that supports 3.3v and 5v CPUs. I also have an IBM 5x86C-100 from a dead ThinkPad 365 laptop. My question is, assuming my motherboard has a 3x multiplier, could I use the 5x86 in that motherboard? The IBM 5x86s run at 3.3v and the little CPU board seems to use the Socket 3 pinout, though I haven't tried inserting it into a Socket 3 socket to find out.

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    Quote Originally Posted by itsvince725 View Post
    I have a 486 system with PCI slots and an Intel i420 chipset that supports 3.3v and 5v CPUs. I also have an IBM 5x86C-100 from a dead ThinkPad 365 laptop. My question is, assuming my motherboard has a 3x multiplier, could I use the 5x86 in that motherboard? The IBM 5x86s run at 3.3v and the little CPU board seems to use the Socket 3 pinout, though I haven't tried inserting it into a Socket 3 socket to find out.
    Drop it in and give it a shot. I can't see where it would irreversibly hurt any thing.
    Surely not everyone was Kung-fu fighting

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    Thanks to the Wayback Machine I was able to find the information for my motherboard and apparently there's no 3X multiplier, only 2X. I'm not gonna bother then, sure the IBM 5x86C is probably a bit faster at 66MHz than the DX2 but I don't know if it would even run underclocked.

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    486s were not multiplier or FSB locked, you can generally set the multiplier/FSB to whatever you want.

    I've run some 66-133 MHz Am486s at 16/25/33 MHz and they worked fine.

    If you wanted to get a 3/4x multiplier, you'd need one of those Evergreen 586 upgrade chips, but they're pretty expensive on ePay.

    https://www.ebay.com/itm/372640945884

    I have a dead one that burned up in a laptop, I need to get around to replacing the CPU on the interposer one of these days.

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    I have an Evergreen 586 processor myself in my Packard Bell Pack-Mate 28 Plus and it works without issues (new). I've also seen a blog that someone took the CPU itself off of the Evergreen CPU that had missing pins for the desktop Socket 1-3 on an IBM ThinkPad 701c laptop and got it set to 133MHz (33FSB x 4) and 16KB L1 WB cache.

    Blog here: https://blog.noq2.net/butterfly-on-s...3-mhz-mod.html
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    It's a shame they didn't try to repair the Evergreen interposer, they're pretty rare these days. You can get Am5x86 PQFP CPUs on Ebay for $20 or so, NoS.

    When I eventually get to repairing mine, I'm just going to use an X-Acto knife to cut the legs off and use a blob of solder to remove the remaining legs, not like the burned CPU is worth anything.

    I wonder how hard it would be to copy the design of the Evergreen interposer and make replicas today. It looks like a multi-layer PCB, I'd imagine it'd be pretty difficult.

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    Quote Originally Posted by GiGaBiTe View Post
    486s were not multiplier or FSB locked, you can generally set the multiplier/FSB to whatever you want.

    I've run some 66-133 MHz Am486s at 16/25/33 MHz and they worked fine.

    If you wanted to get a 3/4x multiplier, you'd need one of those Evergreen 586 upgrade chips, but they're pretty expensive on ePay.

    https://www.ebay.com/itm/372640945884

    I have a dead one that burned up in a laptop, I need to get around to replacing the CPU on the interposer one of these days.
    Hmm, well, the IBM 5x86 probably does perform better at 66MHz than an Intel DX2 does...

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    The IBM is just a rebranded Cyrix 5x86, which was a cut down 6x86; Which was basically a Pentium class CPU.

    The 5x86 was a very buggy CPU, features it was advertised to have and be shipped with (like branch prediction) were disabled because it made the CPU very unstable. Even with all of the advanced features it was supposed to have being turned off in final silicon, it still suffered incompatibility issues with software and motherboards.

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    A shame, as benchmarks prove the Cyrix 5x86 is the fastest Socket 3 CPU ever produced (it easily beats the AMD equivalent at the same clock speed). Socket 3 could have lived on into the Pentium age as Socket 7 did into the Pentium III age had the Cyrix chip been more stable.

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    486 machines did live well into the Pentium 3 age, in fact to nearly the end of it. Upgrades for 486 machines were made all the way until 1999, when AMD ceased to make the Am5x86-133.

    They were still popular machines for people that didn't play games and just needed them for basic home office, email and light internet browsing. Windows 98SE ran fine on a fast 486 with a decent amount of RAM, but many people were still running Windows 3.1 and 95.

    The death knell of the 486 was when AMD stopped manufacturing the chips and Microsoft dropped support for it in Windows XP, which required the CMPXCHG and CPUID instructions. Though, technically you could run Windows XP on a 486 machine by using a POD63/83, it's just painfully slow.

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