The K6-2 550 interprets the 2x multiplier as 6x, which allows it to be run @ 400 to 500 MHz in older Socket 7 motherboards with 66 to 83 MHz frontside bus speeds. My hunch is that the motherboard can't properly display the correct speed, and this is also throwing Linux off. Your best bet is to go back to the 5.5x100 and try and sort out why it's unstable. Maybe try setting the voltage a little higher than stock. Do you have the most up to date BIOS? Retro Web shows the last BIOS is dated 11/11/99; if that's newer than what you have, I'd be sure to update it.

My guess is you have it set to 95x5.5 and bios is guessing 550

At 2x it is probably running at 95x6

Be sure your heatsink and fan and paste are good.
Check voltage.

May have bad mobo caps

Repo Man11 wrote on 2023-09-14, 02:16:

The K6-2 550 interprets the 2x multiplier as 6x, which allows it to be run @ 400 to 500 MHz in older Socket 7 motherboards with 66 to 83 MHz frontside bus speeds. My hunch is that the motherboard can't properly display the correct speed, and this is also throwing Linux off. Your best bet is to go back to the 5.5x100 and try and sort out why it's unstable. Maybe try setting the voltage a little higher than stock. Do you have the most up to date BIOS? Retro Web shows the last BIOS is dated 11/11/99; if that's newer than what you have, I'd be sure to update it.

Thanks, I'd read about a 3x internal multiplier, but that only applies if the motherboard multiplier is set to 2x?

I already did try running 2.4v instead of 2.3v and it made no difference.

The BIOS is not quite the latest. The date is 7/26/1999. I may try an upgrade. I wonder if I can find a BIOS changelog for this.

I can't find the 5SSB on Retro Web. There's a 5SSM, but it looks pretty different. Google actually turns up very little about the 5SSB for me.

Sphere478 wrote on 2023-09-14, 02:52:

My guess is you have it set to 95x5.5 and bios is guessing 550 […]
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My guess is you have it set to 95x5.5 and bios is guessing 550

At 2x it is probably running at 95x6

Be sure your heatsink and fan and paste are good.
Check voltage.

May have bad mobo caps

The jumpers are definitely set to 2x100 right now, I just double checked.

Heatsink/fan/paste is very good, I freshly installed it last night with some MX-4 and I'm using one of those heatsinks that screws down to ensure a good contact. It's nice and tight.

I'll check voltage and investigate caps after I try some other things and still have problems.

My mistake, you're correct I was looking at a 5SSM.

UselessSoftware wrote on 2023-09-14, 03:18:

Thanks, I'd read about a 3x internal multiplier, but that only applies if the motherboard multiplier is set to 2x? […]
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Repo Man11 wrote on 2023-09-14, 02:16:

The K6-2 550 interprets the 2x multiplier as 6x, which allows it to be run @ 400 to 500 MHz in older Socket 7 motherboards with 66 to 83 MHz frontside bus speeds. My hunch is that the motherboard can't properly display the correct speed, and this is also throwing Linux off. Your best bet is to go back to the 5.5x100 and try and sort out why it's unstable. Maybe try setting the voltage a little higher than stock. Do you have the most up to date BIOS? Retro Web shows the last BIOS is dated 11/11/99; if that's newer than what you have, I'd be sure to update it.

Thanks, I'd read about a 3x internal multiplier, but that only applies if the motherboard multiplier is set to 2x?

I already did try running 2.4v instead of 2.3v and it made no difference.

The BIOS is not quite the latest. The date is 7/26/1999. I may try an upgrade. I wonder if I can find a BIOS changelog for this.

I can't find the 5SSB on Retro Web. There's a 5SSM, but it looks pretty different. Google actually turns up very little about the 5SSB for me.

Sphere478 wrote on 2023-09-14, 02:52:

My guess is you have it set to 95x5.5 and bios is guessing 550 […]
Show full quote

My guess is you have it set to 95x5.5 and bios is guessing 550

At 2x it is probably running at 95x6

Be sure your heatsink and fan and paste are good.
Check voltage.

May have bad mobo caps

The jumpers are definitely set to 2x100 right now, I just double checked.

Heatsink/fan/paste is very good, I freshly installed it last night with some MX-4 and I'm using one of those heatsinks that screws down to ensure a good contact. It's nice and tight.

I'll check voltage and investigate caps after I try some other things and still have problems.

See what memtest86+ or chkcpu says

Jumpers/manual may be wrong. Usually the bios rounds to the nearest best guess and software shows the actual. I could be wrong but my bet is that it actually is 525 mhz

100 x 5.5x is still unstable. I even tried going up to 2.5v.

90 x 2x (so 6x internally) gives me a stable 540 MHz, reported by both the BIOS and Linux.

This thing only seems stable with the K6-2 if I use 2x multiplier. It works perfectly fine with other multipliers with other CPUs, I've used a Pentium MMX and a Cyrix MII-366 with no issue.

I had it running Server 2000 on the Pentium with this same RAM for over a week before I shut it down and no problems whatsoever. That included running some intensive games for a while that a Pentium 1 really has no business running, like Deus Ex.

I suppose memtest86 can't hurt though.

EDIT: No, actually I just had a benign/simple program (inxi) cause a kernel crash in Linux with 90x2. Not stable. Could this CPU be defective?

Yes, the CPU could be defective.

You seem to have a stability problem which you're operating on the edge of, depending how you set the clocks.
Make sure the dividers are set correctly (so PCI is running at or close to 33MHz). If that's set wrong, PCI could be at 1/2 of FSB which would put it in the high 40s - which won't be stable.
You might also have dodgy power affecting the CPU or the chipset or the RAM (or everything). This could be caused by bad capacitors, bad power supply, or other failing components on the board.

Prime95 torture test (or mprime under linux) and memtest86 are both very good for checking stability. I like to check at least a few hours of memtest86 before installing an OS.