feipoa wrote on 2024-08-07, 12:19:

Has it been determined if the QFP100 IBM SLC2 chips can run at 3x via software? Or did IBM only unlock the 3x multiplier with the QFP132 series of IBM Blue Lightning chips?

That's a good question. I know the 486SLC2 software has a software switch for the CPU register to activate 2x multiplier, but I don't know if anyone has ever tried using the BL3 supporting software to run an SLC2 in 3x multiplier. I guess all one would need to do is twiddle that one register bit that control the multiplier and see if it will recognize the value of 3, or it only goes up to a value of 2.

However, I'm doubtful it would work. The IBM 486SLC2 is a true SX processor, with BQFP 100 pin package. I think it's highly likely that the IBM 486SLC2 is of an inherently different internal design than the BL3.

pshipkov wrote on 2024-03-29, 07:48:

Pinout is the same as 386dx.
link

I'd like to thank pshipkov for his insight early on regarding the pinout. He was completely correct. I also appreciate his patience in helping me come to the right conclusion.

As well as Feiopa and Furan for their previous research into the subject of 486-like processors that are upgrades for 386 systems and their control software

Mike5G also provided helpful insight and information as well as Anonymous Coward for providing important historical context.

Without all of your collective assistance I couldn't have gotten to the right answer. This truly is a wonderful community.

I guess this definitively proves that a BQFP 100-pin SLC3 never existed, and that IBM, likely for practical reasons, decided to just use a BL3 in 16-bit bus mode instead.

It's a great feeling to finally be on the right track after all these years, since I've been working on this sporadically going back to 2018. Hopefully within the next couple of years I will have a functional hardware prototype interposer and begin working on the software side of things.

This makes me wish I'd asked on here years ago, I wouldn't have wasted so much time. Plus, being a BL3, I likely could have gotten one for less than I paid for the genuine IBM 486SLC3 upgrade riser, which is considerably more rare. Oh, well. Fortunately now that this is known for sure, I can save anyone else in the future from making the same mistake.

I have tried to enable the 3x multiplier on an slc2-66 on an alaris leopard using a software utility. It didn’t work. I suspect that IBM probably did produce some true SLC3s but ended up selling them as SLC2s. More than likely they ended up in portable devices.

Anonymous Coward wrote on 2024-08-07, 23:50:

I have tried to enable the 3x multiplier on an slc2-66 on an alaris leopard using a software utility. It didn’t work. I suspect that IBM probably did produce some true SLC3s but ended up selling them as SLC2s. More than likely they ended up in portable devices.

Now that would be interesting. It would take someone with an extensive collection of SLC2's of IBM origin to know for sure as they could check individual chips for variances and see if any of them responded to the 3x multiplier register command. I don't know of anyone that is a specific collector of SLC2 systems. I'm sure they exist out there somewhere. Everything has at least one collector somewhere that loves them.