It's just like a DX4-100 except its rated to run at 40MHz bus instead of just 33MHz.

All 486DX4's (apart from the Overdrive versions with onboard VRM) ran at 3.3V.
So you need a Socket 3 motherboard that supports that voltage. Older 486's were 5V.
PCI hasn't really got anything to do with it. CPU voltage support is entirely seperate. although since PCI came along towards the end of the 486 lifecycle there's a fair chance that a 486 PCI board will support 3.3V CPUs. It's not a hard and fast rule though. Some non-PCI boards may support 3.3V as well.

You can try and find a voltage adapter that fits between the socket and the CPU although they seem to be fairly rare these days.

Whereabouts in Aus are oyu located? I'm on gold coast 😀

Great thanks for the info. The VLB board I have does support 3.3v I think so I'll check it out, maybe I can just drop it in (and then fiddle with the jumpers).

Gold Coast ey? Nice one. I'm in Melbourne. Out of interest where do you get your retro bits from in this vast, mostly empty land of ours? Not much on eBay.

I had some old stuff lying around from years past. Not much though.
I also had success asking for old bits on a couple of forums such as www.atomicmpc.com.au and www.overclockers.com.au
If you're patient you can sometimes score alright off ebay. Just gotta keep checking it regularly.
You could also try local tip shops if there's one nearby.
Our local council does a free cleanup every 6 months or so and people just leave their junk on the kerb. I like to drive around and rummage through the piles for old PC's 😀 This hasn't been very successful in recent years though. I rarely see anything older than a Pentium machine.

The DX4-120 is probably an AMD (or possibly a Cyrix/IBM).
What does the Pentium Overdrive look like btw?

Yes the DX4 is an AMD. And there are some Cytrix / IBM's in the pile too. It was about 30 chips on final count, more than I'll ever need!

I'm not sure if they are pentium overdrives but they (3 of them) look like this:

http://www.cpu-world.com/CPUs/Pentium/TYPE-Pe … 0overdrive.html

The heat sink is the same anyway, and they are 133's.

2 are complete with fan , but I think I threw the 3rd one's fan out before I realised what it went with (woopsie)

That's quite a score! They're Socket 4 overdrives and I believe they're quite rare.
I'd be interested in buying one to go in my Socket 4 Pentium 60 😁

There were Pentium Overdrives for Socket 3 (486 motherboards), which are probably the most common type. Other Overdrives were made for Socket 5 Pentium and Socket 8 (pentium overdrive).

DonutKing wrote:

I'd be interested in buying one to go in my Socket 4 Pentium 60 😁

Same 🤣, been looking for one for ages.

If you want to sell them, try cpu-world.com if you want a good price 😉

Sorry a closer look revealed them to be ordinary old Pentium 133's and 100's. The heatsinks tricked me (not hard to do).

theRobin wrote:

Sorry a closer look revealed them to be ordinary old Pentium 133's and 100's. The heatsinks tricked me (not hard to do).

Then they are boxed Pentiums. The overdrives for Socket 5 have a different bottom, at least afaik

As far as the socket 5 Pentiums go, if it's an overdrive, the permanently attached fan will be powered by the cpu socket and there will be various components visible between the heatsink and cpu. The boxed retail normal Pentiums won't have anything odd and the built in fan will be powered by a lead from the power supply. Also, the fans on socket overdrives had a black and white or blue and white label while normal Pentiums with the permanently attached heatsink/fan will have a holographic label.

Also, as far as I know, all Overdrives will say Overdrive somewhere and have OPD etched in along with all the other numbers Intel likes to put on their cpus.

Excellent thanks for the info, your description of the 'normal Pentium' matches what I have perfectly.

It's still quite a stylish heatsink and fan, I might find a use for them some day but in the shed they go for now.

I was running an AMD DX4/120 on my VLB 486 build before I found the 5x86-ADZ. It worked great!

What is the speed of an AMD 486 DX4 120Mhz when its de-turbo`t.

Any 486 deturbo speed is motherboard dependent, or more the capability of the clock PLL chip or circuitry that does that function. Often they will deturbo to ISA bus speed when they have a fixed frequency for that, which is 7 point something or 8 even, occasionally they go to 4.77 to attempt PC/XT compatibility, but since anything that only likes that is often exact instruction timing dependent it doesn't help much when you've still got the 2 or 3x multiplier applying to final CPU core speed.

BitWrangler wrote on 2023-08-09, 18:06:

Any 486 deturbo speed is motherboard dependent, or more the capability of the clock PLL chip or circuitry that does that function. Often they will deturbo to ISA bus speed when they have a fixed frequency for that, which is 7 point something or 8 even, occasionally they go to 4.77 to attempt PC/XT compatibility, but since anything that only likes that is often exact instruction timing dependent it doesn't help much when you've still got the 2 or 3x multiplier applying to final CPU core speed.

This is true for modern 486 mainboards with "green" (power saving) functions. Those boards often are able to change the FSB frequency during operation. I indeed have a board at hand the de-turbos to 8MHz (not the ISA clock, a fixed 8 MHz) FSB clock. With a DX4-120, this would be 24 MHz (due to the *3 multiplier) at deturbo settings.

Before 486 mainboards were able to switch the FSB clock (the 486 requires the switch of the FSB clock to be very gentle), de-turbo was often implemented by adding wait states and/or putting the L2 cache into always-miss mode.