willmurray461 wrote on 2024-07-24, 16:27:

Also, I remember reading somewhere that there may exist IBM 5x86C chips with core designs outside of Stepping 0, Revision 5 and Stepping 1, Revision 3. Has anyone actually found one?

I've never heard of something other than Stepping 0, Revision 5 and Stepping 1, Revision 3. I think that's just one of those myths no one can prove just as that John Davis once pronounced “camry” correctly

feipoa wrote on 2025-07-17, 02:40:

My interposers all had i486DX4-100 WT chips on them. They work fine with Cx5x86 and Am5x86 CPUs. If you can find some from China, they are usually very cheap. I sent my contact a message of inquiry about more.

Message me if you hear back. Sounds like an Evergreen Technologies 586 AMD 5X86 upgrade chip could work as well, yes? I imagine you use a hot air station to remove the original chip?

feipoa wrote on 2025-07-17, 02:40:

My interposers all had i486DX4-100 WT chips on them. They work fine with Cx5x86 and Am5x86 CPUs. If you can find some from China, they are usually very cheap. I sent my contact a message of inquiry about more.

So far, my contact has not replied, but he read the message. Either he is still trying to find the interposers, or he isn't interested. Will wait another week, then message him once more.

douglar wrote on 2025-07-23, 01:31:

Message me if you hear back. Sounds like an Evergreen Technologies 586 AMD 5X86 upgrade chip could work as well, yes? I imagine you use a hot air station to remove the original chip?

I doubt those would work, for 2 reasons.

1) most of those Evergreen interposers contain a 1117 VRM, which normally maxes out at 800 mA (some brands note 1 A). According to the IBM 5x86C 3.3V Microprocessor QFP Addendum (Fax #40045), at 100 MHz the minimum current draw is 0.8 A, and max is 1.1 A. How much does the Cx5x86 draw at 150 MHz and, say, 3.7 V? Probably over 1.5 A.

2) those Evergreen interposers have the VRM set to 3.45 V. You would need to modify the interposer with a trimmer to go over 3.45 V. I have done this on one of my Evergreen modules, as well as swapped the VRM for a beefier unit (maybe 3 A). Howvever, there were several revisions of the Evergreen Am5x86 interposer and not all of them have the solder pads for the larger VRM.

Looking into this a tad further, I wanted to see which VRM's were used on interposers containing IBM/Cyrix 5x86 chips.

Gainbery interposer with QFP Cyrix 5x86-100QP
contains 2955 MOSFET = 2.5 A

Gainbery interposer with PGA IBM 5x86-100HF
contains LT1528 = 3 A

Evergreen, with a PGA Cyrix 5x86-133/4x
EZ1086CM = 1.5 A

If you are considering using an Evergreen QFP-PGA interposer and want to upgrade the 1117 VRM, I used an LD1085 w/trimmer on a few of my interposer. However, I've only run them with Am5x86 chips.

feipoa wrote on 2025-07-23, 09:19:

So far, my contact has not replied, but he read the message. Either he is still trying to find the interposers, or he isn't inte […]
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feipoa wrote on 2025-07-17, 02:40:

My interposers all had i486DX4-100 WT chips on them. They work fine with Cx5x86 and Am5x86 CPUs. If you can find some from China, they are usually very cheap. I sent my contact a message of inquiry about more.

So far, my contact has not replied, but he read the message. Either he is still trying to find the interposers, or he isn't interested. Will wait another week, then message him once more.

douglar wrote on 2025-07-23, 01:31:

Message me if you hear back. Sounds like an Evergreen Technologies 586 AMD 5X86 upgrade chip could work as well, yes? I imagine you use a hot air station to remove the original chip?

I doubt those would work, for 2 reasons.

1) most of those Evergreen interposers contain a 1117 VRM, which normally maxes out at 800 mA (some brands note 1 A). According to the IBM 5x86C 3.3V Microprocessor QFP Addendum (Fax #40045), at 100 MHz the minimum current draw is 0.8 A, and max is 1.1 A. How much does the Cx5x86 draw at 150 MHz and, say, 3.7 V? Probably over 1.5 A.

2) those Evergreen interposers have the VRM set to 3.45 V. You would need to modify the interposer with a trimmer to go over 3.45 V. I have done this on one of my Evergreen modules, as well as swapped the VRM for a beefier unit (maybe 3 A). Howvever, there were several revisions of the Evergreen Am5x86 interposer and not all of them have the solder pads for the larger VRM.

I find the voltage regulator on these is redundant anyway unless you plan to use it on a low end board that doesn't have it's own that could be tweaked for the right voltage, or bypassed with an adjustable board like BoBoCoCZ has done. The few times I messed around with AMDs on interposers (now I wish I didn't sell them off) I just jumped the in/out on the vrm anyway and used the motherboards vrm, if one was replacing the CPU with a Cyrix there is really no reason to populate the regulator at all, just bridge it, there's no good reason to have a regulator adding heat the cpu anyway ESPECIALLY with a cyrix

MSxyz wrote on 2025-07-16, 07:26:

Stesch wrote on 2025-07-16, 06:18:

BitWrangler wrote on 2025-07-15, 16:39:

Definitely a Cyrix. Was an early one I think due to having more lsser and btb problems than most, but that might have been the motherboards beta support for it.

Thats impressive! Must have been one of those "magical" CPUs 😁 My IBM 5x86c is currenty running @133Mhz (3x44.52MHz) with 3.58 volts just fine, but 150MHz seems unreachable. So far I've had no luck finding an SQFP variant... Not to mention the unicorn 133GP variant...

Right now, on eBay, there's one person selling 4 brand new 5x86 120 in QFP package and at reasonable price, too. They're rather useless, unless someone comes up with a custom pga to qfp adapter (or recycle of one of those made for Amd 5x86... The pinout should be similar, unlike earlier Cyrix CPUs). Also, there's no guarantee that they will work at a higher frequency (or that they work at all...) and you're not going to discover it before soldering all them 208 pins to the adapter pcb. 😀

(PS: From the pictures the seller provided, the production code appears to be G5A8544B, and they seem to originate from Korea - So they should be step 5 CPUs manufactured in week 44/1995)

Well, there is one less because one is on it's way to me now 😀 I have been watching these for a while wondering if these are the magical 150mhz capable ones #fingerscrossed

bertrammatrix wrote on Yesterday, 02:54:

I find the voltage regulator on these is redundant anyway unless you plan to use it on a low end board that doesn't have it's own that could be tweaked for the right voltage, or bypassed with an adjustable board like BoBoCoCZ has done. The few times I messed around with AMDs on interposers (now I wish I didn't sell them off) I just jumped the in/out on the vrm anyway and used the motherboards vrm, if one was replacing the CPU with a Cyrix there is really no reason to populate the regulator at all, just bridge it, there's no good reason to have a regulator adding heat the cpu anyway ESPECIALLY with a cyrix

Ya, you can do that. It could be more convenient for most people to have a variable VRM on the interposer rather than modify every motherboard's VRM for the 3.45 - 4.0 V range.

bertrammatrix wrote on Yesterday, 03:00:

Well, there is one less because one is on it's way to me now 😀 I have been watching these for a while wondering if these are the magical 150mhz capable ones #fingerscrossed

Please let me know what datecode you end up getting and if it is S1R3. I'm very curious about those G5A9549N chips. Maybve the Korea fab kept pushing S1R3 chips. I've never seen a PGA or QFP chip go past 9544.

I ended up with four of G5A8544B. Compared to G5A9549N, the 4th character, that is, "8 vs. 9", this is the die run. The 8th character, that is "B vs. N", these are the lot numbers. For the difference with 4x vs 3x chips, I found the 4th character to be the probable identifier. For this comparison, it is also the 4th character which is different. I have no idea if this translate to rev/step, but I guess we'll find out soon...

I went through some of the markings on QFP Cyrix 5x86 chips I previously had on interposers. I found some that were G5A9, namely:

G5A9601F
G5A9548G

Both were S0R5. On the bottom, both have "1995 Cyrix USA Korea."

G5A9548G is quite close to G5A9549N and strongly suggests that these G5A9549N chips are S0R5.

bertrammatrix wrote on Yesterday, 03:00:

Well, there is one less because one is on it's way to me now 😀 I have been watching these for a while wondering if these are the magical 150mhz capable ones #fingerscrossed

I will cross my fingers for us both, because I was able to aquire one too 😀 But shipping across the big pond will take a while...