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Olivetti PCS embedded 486 SX-25 with DX4-75 Overdrive - Not working (maybe)

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First post, by Tmp2k

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So I have an Olivetti PCS-44/C, it comes with an embedded 486 SX-25 and a 139pin socket that takes a co-processor or an overdrive chip. I've finally managed to get a DX4ODP75 CPU. Reading the manual it says there are 2 jumpers and they are both set to 1-2 in all cases except for "OverDrive II" where one of them is set to 2-3.

After adding the CPU the machine still boots and it seems faster (not really sure though). When I go into BIOS there's nothing to say what CPU is present, although it says Maths Processor Enabled (does the SX have a maths processor?). However under "Shadow Memory" where it should say "Enabled/Disabled" I just get gibberish Photo -> https://photos.app.goo.gl/xKPvdCu7vpyfAR4JA

I don't have much on there to test, just a blank DOS and Windows 3.1 install. Windows hangs on the splash screen most times, I've tried /S and /3 and when I tried /B to log the error it actually worked.

So my questions are...

What's the difference between overdrive and overdrive II?
What could the jumper settings be for?
How can I test what speed the CPU is actually running at?
Any idea what's going on with the corrupted BIOS?

Reply 1 of 2, by Tmp2k

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So I finally fixed this today, I removed the Overdrive CPU and still had the same issues, wouldn't load windows and got gibberish under the Shadow RAM setting in BIOS. It was at this point I realised that maybe the CMOS memory had become corrupt. So I cleared CMOS, the shadow RAM setting returned to normal and everything worked. I then reinstalled the Overdrive processor and *boom* everything works 😁

So my only question is, what I can I run on DOS/Win3.1 to check/test my clock speed?

Reply 2 of 2, by weldum

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you can use the Phil's Dos benchmarks pack, first benchmark with the slow SX 25 and then bench the Overdrive to see if there's a difference

DT: R7-5800X3D/R5-3600/R3-1200/P-G5400/FX-6100/i3-3225/P-8400/D-900/K6-2_550
LT: C-N2840/A64-TK57/N2600/N455/N270/C-ULV353/PM-1.7/P4-2.6/P133
TC: Esther-1000/Esther-400/Vortex86-366
Others: Drean C64c/Czerweny Spectrum 48k/Talent MSX DPC200/M512K/MP475

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