Pentium on a 386 Motherboard
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I think that's correct though. From what I can find, Intel renamed 586 to 586SX after they released their MMX capable Pentiums. So "non-MMX Pentium" is supposed to be 586SX. "MMX Capable Pentium" is 586DX.
After that came the 80186, which was not used in IBM compatible PCs (but in non-compatible ones) because it was more of a microcontroller and came with integrated but incompatible peripherals (like an interrupt controller). The CPU itself was still compatible, though.
So were 80286, 80386, 80486 and everything after that. They all added stuff obviously, often massively, but they still all can run 8086 software. Though I've lost track of what's happening with Intel CPU as of recently, I just have some dim and unreliable recollection that real mode might finally have been removed altogether, not sure.
Should read "until the 486, before the Pentium".
I don't think there was ever an Intel 786 though.
286 --> 386 --> 486 --> 585
The SX DX thing happened at the 386 and 486 level. All a bit confused and boiled down to whether you got a maths co-processor or not.
Looking back it was a pretty rubbish thing. We consumers have been treated like complete twats by all CPU manufacturers for decades.
That was only on the 486DX which had a math coprocessor vs 486SX which did not.
https://dfarq.homeip.net/386sx-vs-386dx-a-misunderstood-diff...
"DX holds a component identifier and revision number after RESET as Figure 10-1 illustrates. DH contains 3, which indicates an 80386 component."
From the 80386 programmer's reference manual: "DX holds a component identifier and revision number after RESET as Figure 10-1 illustrates. DH contains 3, which indicates an 80386 component."
Starting with the Pentium Pro and the Pentium II, Intel started using non-standard logic levels (which they patented). This effectively made Intel motherboards incompatible with non-Intel CPUs, and previous generations of Intel CPUs.
Other CPUs that might work in a 386 socket: AMD (up to K6-III), and various other Socket 7 CPUs (including a very rare MIPS chip!)
It's actually a standard (JESD8-3), but the patent is mentioned in it as 5023488 and it's not owned by Intel. It expired in 2010.
I kinda don't believe this, but I'm too lazy to look up old datasheets.
Uh... sure, if you say so.
Though, given how it might be using low power (and maybe with some overdrive adaptor quirk), it might have worked this time
> Voltage levels from the chipset?
Wasn't it just 3.3V at the time (or maybe even 5V)?
> Bios recognition?
Not necessarily? Software-wise, a Pentium is still compatible with a 486, and 486s did not even have CPUID yet (only some later steppings did). The BIOS might have not set some bits in some of the control registers as it would otherwise do, but that does not prevent the CPU from working...
> IO timing diagrams?
That's the hardest one, but remember that this was not a "true Pentium" but an "Overdrive", which is basically a Pentium with a 486 bus interface. And the board does accept 486s.
Or perhaps put in a FPGA...
Don't even necessarily need it to be an x86 emulator. Use the motherboard as an oddball I/O facility. An ARM machine (ab)using ISA cards would be an odd duck. Throw in a software x86 emulator with a bridge to the ISA bus for added compatibility. Of course there are simpler ways...
All that said, I'm not sure exactly what the benefit really is other than having a cool project. But thats maybe the point. Maybe that's enough in itself.
Consider what else happened in the 386 through Pentium transition:
* The PCI bus became standard; your peripheral cards all needed to change.
* SDRAM became standard; the memory bus became significantly wider / faster, and you bottlenecked on RAM if you used older mainboards.
* IDE, while it was already used for hard drives, was now used for your CD drive too - you probably wanted a CD drive and not a second floppy drive (different controller) in your machine, which was harder if you only had a primary IDE bus.
I bought the motherboard, CPU and RAM. Half the cost was the 8MB of RAM. CPU was the next most expensive item.
Worked fairly well, but it was speed limited in certain cases by the 386 motherboard/memory combo. Also not all applications/games would run since they didn't properly detect it as a proper 486.
[1]: https://ancientelectronics.wordpress.com/tag/486-in-386-moth...
As far as I'm concerned, the point of ricing is to see what can be achieved with exotic configurations. I'm running a Ryzen 3950X in a B350 board, which is barely supported, but it works fine. Memory speed is at the edge of stability, which isn't much on that board - about 2900 MHz. My "benchmarks" are compile times.
For old computers, I don't care which benchmarks, as long as they are the same in the "before" and "after" configurations.
My first computer had a 486DLC. I had no idea at the time that it's close to a 386 and is a little slower than a 486SX-25. But I was in school and I had to take what my parents were willing to pay for. It would be fun to see what could have been achieved with a crazy CPU swap. I guess a board that could take an almost 486 could also take a Pentium Overdrive as in the article.
And I hadn't seen the name weitek in.. Well I can't remember!