Be more specific. There were ceramic CPUs up to the Pentium Pro.

If you are talking about 386/486DLC, as question 3 suggests, it's easy:

1. there's no multiplier, they run at bus speed
2. nothing will happen, they don't need any cooling
3. no, see 2
4. no, even socket 7 CPUs still had the sensor in the socket, not in the CPU. Slot 1 afaik as well.

Thanks, I meant the ceramic CPUs from 386 to Pentium Pro.

What about the multiplier and heat of 486/586/686/Pentium?
Even 486DLC runs so hot too =/

Well the fastest 486DX4 had a power dissipation of (min/avg/max) of ~0.33/~3.55/~5.22 Watt's respectfully.
Pentium (a.k.a. 586) is where the notion of TDP came into being. A Pentium 166 had a TDP of 14.5 Watt's.
Both are not that much in today's terms.

But the Pentium Pro 200 (686) was 37.9 Watt's... A huge jump for the time.

Anything over 25/33Mhz should have some heatsink; anything over 166Mhz should have a fan. That's OEM. But some slower ones did have fans and/or heatsinks anyway; this is just sort of the limit I have encountered.

Early ones are glued on with some substance (thermal...glue?), later ones obviously have the metal clip which catches the tabs on the side of the socket to hold the heatsink.

Oh, and obviously the 166Mhz Pentium heatsink is a lot larger than the 100Mhz 486 one.

for what it's worth I always add at least a heatsink on 486DLC cpus, they run too hot for my taste BUT I have never seen an old mobo with a 486DLC that has a heatsink (at least the ones I have seen) so this is proof they are made to be hot. Still 30 years later it's better to be safe 🤣

RiP wrote on 2020-01-10, 07:13:

Thanks, I meant the ceramic CPUs from 386 to Pentium Pro.

What about the multiplier and heat of 486/586/686/Pentium?
Even 486DLC runs so hot too =/

For 486SX/DX CPUs you can run them safely without a heatsink.
For 486DX2 CPUs that run at 3.3V you can run them safely without a heatsink.
For 486DX2 CPUs that run at 5V and all DX4 and beyond CPUs, you need a heatsink
All AMD 5x86 CPUs require a heatsink and a fan
You can run Pentium CPUs up to and including Pentium 133 with a heatsink
Pentium CPUs running at 150MHz and above require a heatsink and a fan
All AMD K5 CPUs require a heatsink
All Cyrix 5x86 CPUs require a heatsink and a fan
All AMD K6 CPUs require a heatsink and a fan (although technically ceramic, these have a heatspreader)
All Cyrix 6x86 family CPUs require a heatsink and a fan (although technically ceramic, these have a heatspreader)

While the above list provides a good ballpark in reality it is slightly more complicated.

For example "All AMD 5x86 CPUs require a heatsink and a fan". In fact different versions have requirements. For example the popular ADZ version, while the fan is recommended can be operated with just a heatsink or even without any cooling as far as you don't exceed ambient and case temperature. Of course these are much easily achieved with heatsink w/fan. but also with sufficient airflow or other methods. Similar rules apply to other CPUs.

I would rephrase the answer as: "as you exceed 50 MHz you should pay attention to cooling".

Thanks all! What about the multiplier?

keropi wrote on 2020-01-10, 08:25:

for what it's worth I always add at least a heatsink on 486DLC cpus, they run too hot for my taste BUT I have never seen an old mobo with a 486DLC that has a heatsink (at least the ones I have seen) so this is proof they are made to be hot. Still 30 years later it's better to be safe 🤣

Right, I found 486DX-33 hot too.

Right, I found 486DX-33 hot too.

Objection: Meatbag temperature observation isn't exactly accurate.