I've never seen one with a 3.3V fan.
They probably don't run at their rated speed but still plenty fast at ~3.5V.

It's more plausible to assume that fan contact pads are directly connected to 5V, bypassing voltage conversion.

The Serpent Rider wrote on 2023-05-05, 10:32:

It's more plausible to assume that fan contact pads are directly connected to 5V, bypassing voltage conversion.

5V is not plausible on a Socket 5 CPU.

CMR779 wrote on 2023-05-05, 01:38:

Hey friends, I've got a pentium overdrive processor I was going to use. It's a PODP3V150, but the fan that came on it was rated for 5V. Every pic I've seen online also shows 5V fans for these things. Is this correct? Do all these processors come with a 5V fan? I'm curious about this because these things seem to get their power from the processors themselves, but the board has to be configured for 3.5Volts. If you're curious, my board is an MTI R-539

https://theretroweb.com/motherboards/s/m-tech … ti-ris-r539-mig

The original socket 5 spec called for I believe 2 5v pins labeled vcc5

I don’t think all motherboards routed them though. By ss7 I believe they were basically NC

I haven’t had a reason to check motherboards to verify though. But a 5v supply was definitely in the original spec for the beloved socket 5

The fan may be running at 3.3v

You can test the voltage at the fan pads on the processor if you are curious.

Did a little digging.

Here is a screen from the POD datasheet.

Shows vcc5

However the datasheet for a normal vanilla pentium 1 shows Internal No Connection on these pins.

So there is a good chance that the fan actually is running at 5v

Thanks for all the replies. I think you're probably right that there were separate rails for the fan because I can't find any with pics showing a 3v rated fan. I'll assume the fan is correct. Worse case, like someone mentioned, is that it might run a little slower.

Sphere478 wrote on 2023-05-06, 00:59:

Did a little digging. […]
Show full quote

Did a little digging.

Here is a screen from the POD datasheet.
IMG_2835.png
Shows vcc5

However the datasheet for a normal vanilla pentium 1 shows Internal No Connection on these pins.IMG_2836.png

So there is a good chance that the fan actually is running at 5v

Interesting. Found a German source that claims some S5 boards supply 3.3V and some supply 5V to pins meant to power an Overdrive fan while all S7 boards supposedly supply 3.3V.
http://www.dickhardtstrasse.org/Hardwarehandb … ml?cpu_586.html

Doornkaat wrote on 2023-05-06, 08:25:

Sphere478 wrote on 2023-05-06, 00:59:

Did a little digging. […]
Show full quote

Did a little digging.

Here is a screen from the POD datasheet.
IMG_2835.png
Shows vcc5

However the datasheet for a normal vanilla pentium 1 shows Internal No Connection on these pins.IMG_2836.png

So there is a good chance that the fan actually is running at 5v

Interesting. Found a German source that claims some S5 boards supply 3.3V and some supply 5V to pins meant to power an Overdrive fan while all S7 boards supposedly supply 3.3V.
http://www.dickhardtstrasse.org/Hardwarehandb … ml?cpu_586.html

That sounds plausible. And would probably work fine. I suspect that they added these during planning of socket 5 but I don’t think any cpus spare overdrive? ever used them

They probably figured they would do the same thing they did on 3.3v socket 3 where it has a 5v vcc5 pin there was also some variation in how that was implemented also.

I know the TI sxl2 was specced for 3.3 and 5v on that pin depending on model but that cpu isn’t a true socket 3 cpu but the pinout is very similar.

In any case yeah, I don’t see any reason what you found couldn’t be the case. It’s plausible. Most cpus in the 5/7/ss7 lineup just ignored those pins. Motherboard manufacturers may indeed have decided not to route the 5v and instead just gave it 3.3v figuring it was good enough. I mean, If you are designing a ss7 mobo in the late 90’s you aren’t expecting someone to put a overdrive in it. So if the fan runs slower for someone who did you probably are like, eh, you are weird but it works. So good enough. Get a k6 when you can afford one. Tech support case closed.